Explanatory note: This page grew out of one of my investigations for Open Phil, but then I got fascinated and put a bunch of personal time into elaborating certain parts of it, and it evolved into something that I think is pretty cool, but which would take more work than it’s worth to vet and edit it such that it would be appropriate for Open Phil’s website, so we decided I should just post it here instead as a personal project. Hence, the below doesn’t represent Open Phil’s position on anything, and should be taken merely as my own personal guesses and opinions.

(Probably best to start with my companion blog post.)

One way to look for opportunities to accomplish as much good as possible is to ask “Which developments might have an extremely large impact on human civilization, ¹ and is there any way we can (in expectation) nudge those developments in a positive direction?”

For example, in the context of philanthropy, the Rockefeller Foundation funded work on an improved agricultural approach that led to the Green Revolution, which some people have credited with kickstarting the development of the “Asian Tigers,” helping several countries transition from “poor” to “middle income,” transforming India from being in the middle of a famine to being a wheat exporter, and saving over a billion people from starvation. ² Of course, the Rockefeller Foundation had no way of knowing their funding would have such incredible impact, but a rare win of that magnitude can make up for a large number of failed (and similarly uncertain) funding efforts. (See Holden Karnofsky’s hits-based giving.)

However, some future developments might have even greater impact than the Green Revolution, and be more comparable in magnitude to the changes often attributed to the industrial revolution. Here, I refer to changes of this magnitude as “transformative,” ³ and I refer to developments which might precipitate such transformative changes as potential “transformative developments” for human civilization. ⁴

In the future, I hope to spend more time identifying potentially transformative developments, ⁵ especially those which might also be tractable and neglected. In this report, I hope to lay some groundwork by examining the magnitude of “transformative” change. In particular, I ask:

• The industrial revolution is often considered the most transformative event in recorded history. ⁶ How large, exactly, were the differences in human well-being before and after the industrial revolution? [more]
• Have there been other transitions in recorded history of comparable magnitude, either positive or negative? [more]
• How catastrophic would a development need to be to plausibly result in negative transformative change? [more]
• What do these initial findings suggest about potential future transformative developments? [more]

My initial tentative conclusions from this preliminary investigation can be summarized as follows:

The gains in human well-being observed since the industrial revolution are vastly larger than pre-industrial fluctuations in human well-being. No other transitions in recorded history, either positive or negative, are remotely similar in magnitude. When thinking about which future developments might be most important, we should not forget that the size of their likely impact may differ by orders of magnitude. For example, a universal cure for cancer would bring a huge benefit to human well-being, but its expected impact seems likely to be vastly smaller than (for example) the likely impact of AI systems capable of automating most human labor, or the counterfactual benefit of preventing large-scale nuclear war.

Human well-being before and after the industrial revolution

How large were the differences in human well-being before and after the industrial revolution?

My strategy for providing a preliminary answer to this question is the following:

1. List some key aspects of human well-being.
2. Find measures for those key aspects of human well-being, for which we have estimates going back to (say) 1000 BCE.
3. Chart the data for each measure, from 1000 BCE – 2000 CE.
4. Inspect the magnitude of the difference in these measures between the pre-industrial and post-industrial eras.

To compare human well-being “before” and “after” the industrial revolution, I need to clarify which time periods I have in mind. Typically, the industrial revolution is considered to have occurred in Britain from roughly 1760-1830. ⁷ As we’ll see below, while very large differences in human well-being took many decades (after the industrial revolution) to accrue, the “trajectory change” (i.e. the “bend in the curve”) for many global measures of human well-being occurred either toward the end of the industrial revolution or shortly thereafter (say, from 1800-1880). Hence, for my purposes, I’ll refer to the period from 1000 BCE to 1760 as the “pre-industrial” era, and the period after 1800 as the “post-industrial era.” (For ease of analysis across multiple data sources, I limit my analysis up to the year 2000.)

For convenience, I’ll assume the apparently common view ⁸ that the “industrial revolution” (what collection of events is that?) is not just coincident with, but in fact is the primary cause of the major trajectory changes observed during this period, but I should be clear that I think this is quite plausibly wrong, and certainly hard to prove. In any case, my primary focus here is to try to assess the magnitude of the changes that occurred during this period, not to argue for a particular causal story. ⁹

Key aspects of human well-being

How should we define human well-being? Without aiming for philosophical precision, ¹⁰ here are some aspects of human well-being that seem especially “fundamental” to me:

1. Subjective well-being (positive feelings, absence of negative feelings, a sense of satisfaction with one’s life, a sense of meaning and purpose, self-esteem, etc.)
2. Physical health
3. Economic well-being (income, wealth, etc.)
4. Three aspects of empowerment to live the kind of life one wants: ¹¹
   1. Energy capture (it’s easier to build your own house with power tools that pull large amounts of energy from the power grid than it is to do so without access to such large energy resources)
   2. Technological empowerment (you can’t use power tools to build your house if power tools haven’t been invented yet)
   3. Political freedom (you can’t build your own house if others prevent you from doing so)
5. Social well-being (trust, community participation, social capital, relationship satisfaction, social support, etc.)

No doubt this particular list is controversial. One could easily (and perhaps persuasively) argue for some other list of key aspects of human well-being; I discuss some alternate possibilities in Appendix A.

Long-run measures of human well-being

Unfortunately, my choice of measures for the aspects of human well-being listed above is heavily constrained by the limited availability of long-run data. In particular, I was not able to find any useable long-run measures for subjective well-being or social well-being, since these aspects of well-being have been measured only quite recently. ¹²

After some searching, the long-run measures of human well-being I settled on for this report are:

• Subjective well-being: no long-run measure available.
• Physical health: life expectancy at birth.
• Economic well-being: GDP per capita and percent of people living in extreme poverty.
• Energy capture in kilocalories per person per day.
• Technological empowerment: Ian Morris’ score for war-making capacity.
• Political freedom: percent of people living in a democracy.
• Social well-being: no long-run measure available.

In the sections below, I explain the rationale behind each measure, chart each measure over time, and discuss potential alternative measures that I chose not to examine here.

Physical health

Life expectancy at birth

First, let’s look at physical health, as measured by life expectancy at birth. Life expectancy at birth is a pretty good proxy for how physically healthy people are in general, since it sums together in a single measure the assaults on physical health we worry most about — malnutrition, infectious disease, physical violence and war, physical injury due to accidents and natural disasters, etc. — and also captures the success of efforts to preserve people’s physical health, such as food supply, public health measures, efforts to preserve peace both within and between societies, etc. (Note also that improvements to life expectancy at birth are not entirely due to falling rates of childhood mortality: see here.)

What does the long-run history of life expectancy look like? According to Roser (2016a):

Estimates suggest that in a pre-modern, poor world, life expectancy was around 30 years in all regions of the world. In the early 19th century, life expectancy started to increase in the early industrialized countries while it stayed low in the rest of the world… Since 1900 the global average life expectancy has more than doubled and is now approaching 70 years. No country in the world has a lower life expectancy than the the countries with the highest life expectancy in 1800.

According to available data, it seems there was a sharp upward bend in the trajectory for life expectancy in Europe following the industrial revolution, with delayed trajectory changes for countries that industrialized later (such as China and India):

If we chart global average life expectancy from 1000 BCE to 2000 CE, using a slowly rising line to represent the apparent view of historians that average life expectancy probably fluctuated between 25 and 30 (and probably rose slightly over time), ¹³ the long-run history of life expectancy looks like this:

If we had true data covering pre-industrial times, we would no doubt see downward spikes in global life expectancy as a result of major catastrophes such as the Black Death. However, as far as I can tell, in all such cases life expectancy recovered quickly to (roughly) the previous status quo, and no such catastrophes produced a lasting trajectory change in global life expectancy. (See also below.)

If we believe these estimates, then pre-industrial, global average life expectancy may have changed over time by as much as ~5 years. In contrast, the difference between pre-industrial and post-industrial global average life expectancy (at their highest points) is more than 7 times that amount, at ~36 years (through 2000 CE).

Other measures of physical health

Below I list some other measures of physical health and briefly explain why I didn’t use them in this report.

• Adult height is commonly used as a proxy measure for physical health, since poor health in childhood or adolescence can lead to growth stunting. Also, height can be inferred from bones, which are available even from ancient times. ¹⁵ However, in the time I devoted to this project, I wasn’t able to make a confident-enough estimate of pre-industrial, worldwide average heights over time for me to include adult height in this report. ¹⁶
• One could also examine long-run trends in the key factors of physical health and mortality that are aggregated together in life expectancy at birth — for example child mortality, maternal mortality, the global burden of disease, hunger and undernourishment, healthcare provision, war, homicide, and others — but these seem less fundamental to me than the measure that sums them all together. ¹⁷
• Vitality is a measure of “having energy, feeling well-rested and healthy, and being physically active.” ¹⁸ Unfortunately, this measure has not been used until fairly recently.

Economic well-being

GDP per capita

Next, let’s look at the long-run history of economic well-being, as measured by GDP per capita. OECD (2014) explains this measure’s relevance to human well-being:

Economic well-being – people’s command over produced goods and services – can be assessed in an historical perspective through measures of gross domestic product (GDP) per capita… GDP (per capita) is an important indicator for measuring the economic performance of countries, which is a central driver of people’s economic well-being. This is true not only because an increased output of goods and services, which is what GDP measures, tends to translate into an increased ability by residents to buy these goods and services, but also because higher GDP provides the means for spending on non-material components of well-being, such as education and health.

What is the long-run trend of GDP per capita? Below I chart a series of historical GDP per capita estimates, adjusted for differences in cost and living across time and space:

In short, world GDP per capita (in 1990 international dollars) was relatively flat until the final decades of the industrial revolution, when the trajectory for this measure changed dramatically. By DeLong’s estimates, world GDP per capita hovered around 90-200 from ancient times up through 1800, then jumped to 300 by 1850, 679 by 1900, and up to 6,539 by 2000.

If we zoom in on the period from 1 CE to 1800 CE, we can see that (using DeLong’s estimates) GDP per capita actually fluctuated a fair bit during the pre-industrial era:

Data from DeLong (1998). Image generated by the author. ²⁰

It is all the more striking, then, that these fluctuations are so small compared to the post-industrial rise in GDP per capita that they show up as a flat line when charting GDP per capita (on a linear scale) in a way that includes the post-industrial era. ²¹

Extreme poverty

Another important measure of economic well-being is percentage of people living in extreme poverty. Extreme poverty is especially relevant to well-being due to the diminishing marginal impact of money on well-being: a $500 gift boosts well-being more when given to someone living on $2/day ($730/year) than when given to someone living on $50,000/year.

The short history of extreme poverty is this: for nearly all of history, nearly everyone lived in extreme poverty. ²² More precise estimates of the proportion of world population living in extreme poverty (under various definitions) pick up the story starting in 1820:

In the chart above, “extreme poverty” (the red line) means living on less than $1/day, and “poverty” (the green line) means living on less than $2/day — both measures adjusted for cost of living (PPP).

If we represent pre-industrial times using a gradually rising line to represent a very slowly rising percentage of people not living in extreme poverty, the long-run trend for this measure looks like this:

Other measures of economic well-being

Other measures of economic well-being I could have used include:

• Other levels of poverty: I could have chosen different thresholds for what counts as “extreme poverty,” for example $5/day or even $20/day. This would result in somewhat different curves, but I suspect the overall story would remain the same.
• Other measures of production, expenditure, and income: In theory, GDP is equivalently a measure of production, expenditure, and income, because your expenditures are my income, my expenditures are your income, and so on. In practice, GDP is never perfectly known, and different ways of trying to measure production, expenditure, and income lead to somewhat different results. Hence, I could have used other measures of average production, expenditure, or income, but I used GDP per capita because it is the most widely available estimate over time and space.
• Economic inequality: Human happiness seems to respond not just to absolute income, wealth, and consumption, but also to relative income, wealth, and consumption. ²⁵ However, the details probably vary from culture to culture, and from person to person. One person may primarily compare their income to that of their co-workers, while another compares their income to that of their neighbors, while yet another compares their income to that of others in their city or country. Moreover, people may compare themselves to others on a complex and individually unique mixture of income, wealth, consumption, disposable income, and other variables. Perhaps the easiest inequality measure to use would be global income inequality. ²⁶ However, I doubt this is a particularly good measure of human well-being, relative to the ones I use here, because comparisons within a country or city are probably far more salient, and because the post-industrial rise in global economic inequality is generally a result of some nations escaping widespread extreme poverty for the first time in history, rather than a result of some nations or people becoming poorer than they used to be. Unfortunately, long-run global averages of local economic inequalities are not available. ²⁷
• Economic mobility, especially various measures of absolute mobility (since relative mobility is a zero-sum game), could be a useful complement to the measures I discuss above. ²⁸ Unfortunately, I’m not aware of long-run estimates for such measures.

Empowerment via energy capture

Morris (2013), ch. 2, explains the centrality of energy capture as a measure of human empowerment: ²⁹

Energy capture must be the foundation for any usable measure of [human empowerment]… Without capturing energy, humans (like plants and other animals) die. Similarly, unless they take up energy from their environments, the societies humans have created break down. To increase their mastery of their physical and intellectual environments and get things done, groups of people have to increase their energy capture.

In other words: to get anything done, you need to capture energy from your environment and use it to do the work of accomplishing your goals. Given (almost) any set of goals, they will be easier to accomplish with more energy devoted to them.

Or as Smil (2017), p. 1, puts it:

Energy is the only universal currency: one of its many forms must be transformed to get anything done… From a fundamental biophysical perspective, …the course of history can be seen as the quest for controlling greater stores and flows of more concentrated and more versatile forms of energy and converting them, in more affordable ways at lower costs and with higher efficiencies, into heat, light, and motion.

Energy capture includes: ³⁰

• Food: directly consumed, fed to labor animals, or fed to animals later consumed.
• Fuel: used for cooking, heating, cooling, powering machines, etc., and provided by wood, coal, oil, gas, wind, water, nuclear, etc.
• Raw materials: for clothing, construction, pot-making, metalwork, or any other purpose.

Defined this way, energy capture is clearly related to GDP, though it is a different and broader, and thus partly independent, concept.

Drawing on a very wide range of historical sources and types of evidence, Morris estimated energy capture (in kilocalories per person per day) from 10,000 BCE to 2000 CE — not for the entire world, but for the (moving over time) “cores” of Western and Eastern civilization. Below, I chart his estimates starting from 1000 BCE:

Here, we see a very slow rise in energy capture per capita up until just after 1800, when energy capture per capita skyrockets upward in both the Western and Eastern cores.

I haven’t found global estimates of energy capture per capita over such an extended period of time. If such estimates could be constructed, my guess is that the hockey-stick curve seen here would be attenuated somewhat because energy capture is presumably smaller per capita outside civilizational “cores” (at any given moment in time).

Empowerment via technology

War-making capacity

What measure can we use to estimate humankind’s technological empowerment, stretching back thousands of years? After surveying the options, I concluded that the best available measure for present purposes is Morris (2013)‘s measure of “war-making capacity.”

It might seem odd to use war-making capacity as a measure of human well-being, but consider the likely correlation between war-making capacity and other sorts of technological empowerment more obviously promoting of well-being. A society that can fly bombs to the other side of the world in mere hours can also transport humans and goods anywhere in the world in mere hours (whereas previously it would’ve taken weeks, months, or years). And a society that can mass-manufacture chemical and biological weapons carefully engineered for devastating effects has probably also discovered (or will soon discover) how to mass-manufacture synthetic fertilizer and penicillin.

Moreover, relative to other measures of technological empowerment, war-making capacity has several practical advantages as a proxy for technological empowerment:

• Unlike many other measures of knowledge and technology, war-making capacity focuses well on the “empowerment” aspect of knowledge and technology. For example, Maxwell’s equations represent a fundamental advance in human knowledge, but someone who learns them is not thereby much more empowered to achieve their goals, until someone uses Maxwell’s discoveries to develop new (e.g. electric) technologies, including those used in war.
• War-making capacity is also an unusually “concrete” measure of empowerment, in the sense that an actor with greater war-making capacity will prove its higher level of empowerment in a concrete way: by winning conflicts with actors at a lower level of empowerment (e.g. as seen during various waves of colonization).
• We have unusually good historical data (and syntheses of data) concerning war-making capacity, due to “historians’ obsession with recording wars, compulsive military record keeping, artistic patrons’ fondness of being portrayed as warriors, the widespread practice of burying dead men with arms and armor, [and] the archaeological visibility of fortifications…” ³²
• War-making capacity is a measure with relatively continuous meaning across thousands of years (unlike, say, patents).

Morris’ measure of war-making capacity is a purely relative one, answering questions such as “In 400 BCE, how powerful was the military of the Persian Empire (the Western ‘core’ at that time) compared to that of Egypt-Syria-Iraq (the Western ‘core’ of 700 CE) in 700 CE?” (The details are complicated, and I leave them to a footnote. ³³ ) Also, as with his measure of energy capture, Morris estimated war-making capacity only for the (moving over time) “cores” of Western and Eastern Civilization. Here are the results:

Granted, this does not show much beyond the fact that differences in war-making capacity prior to the industrial revolution are completely dwarfed by differences in war-making capacity on either side of the industrial revolution. ³⁵ But, this is an important historical fact worth remembering, and one that might be forgotten in detailed discussions of the military importance of pre-industrial war-making innovations such as chariots or cavalry, which represent much smaller increments of technological empowerment than planes, tanks, and nuclear weapons do.

Other measures of technological empowerment

Other measures I considered include:

• Peregrine’s Atlas of Cultural Evolution (ACE) is more a measure of “cultural complexity” than a measure of how “empowered” a civilization is. Moreover, it isn’t intended to capture the transformative changes of the last few centuries, which is why Peregrine’s charts all go up to 1500 CE and no later.
• Some sources use variables such as R&D investment or patents (e.g. Coccia 2014), but these data are only available for very recent times.
• Comin et al. (2010)‘s technology dataset includes only three “snapshots” of technological development: in 1000 BCE, 0 CE, and 1500 CE.
• Dong et al. (2016)‘s bibliometric approach is interesting, but unfortunately I was not able to obtain a copy of the dataset, and the earlier publications describing the dataset in more detail are available only in Mandarin.
• Murray (2003)‘s tables for “central events in various sciences” could provide another biblioemtric dataset, but Murray’s approach leaves out “technological” developments, and isn’t much of a measure of how “empowered” a civilization is by its knowledge and technology.
• I could also have used Morris (2013)‘s measure of information technology over time, but this seemed somewhat worse for measuring how “empowered” a civilization is by its knowledge and technology, compared to Morris’ measure of war-making capacity.

Empowerment via political freedom

Democracy

Since democracies tend to be more responsive to the desires of their citizens than other types of regimes are, and tend to do a better job of preserving human rights, one proxy measure for political freedom is percentage of people living in a democracy. The long-run trend for this measure looks like this:

Since my source for which regimes count as “democracies” is the Polity IV dataset, and Polity IV only provides ratings back to 1800, the chart here shows a drop from 0.69% of people living in a democracy in 1800, to 0% of people living in a democracy for every year prior to 1800. That is of course somewhat inaccurate, but I’m confident that if Polity IV had tried to score regimes for their degree of democracy prior to 1800, the overall trendline would look much the same: i.e. nearly 0% of people lived in a democracy (as Polity IV defines them) until near the end of the industrial revolution, after which the percentage of people living in a democracy skyrocketed upward.

Other measures of political freedom

Below I list some other measures of political freedom and briefly explain why I didn’t use them in this report.

• Slavery: Perhaps the best measure of empowerment via political freedom would be “percent of people not enslaved,” since slavery typically removes or curtails a broad variety of political freedoms all at once. Unfortunately, it would be difficult (and perhaps hopeless) to try to draw lines between the different forms of slavery and bondage experienced in different cultures and centuries throughout history, and in any case we lack the data to make such estimates. See below for details on my aborted attempt to estimate “percent of people not enslaved” over time.
• Measures of some other human rights (besides protection against enslavement) could be considered, but these raise difficult measurement questions, and in most cases we lack estimates for all but the most recent decades.
• Percent of people politically enfranchised: I haven’t seen these data estimated over time, but presumably it could be done, using data on when different regimes granted and withdrew voting rights from different subpopulations (e.g. women). ³⁷ If we had these estimates, I suspect the curve for this measure would look much the same as for “percentage of people living in a democracy,” except that it would rise later and more gradually.

Summary of human well-being before and after the industrial revolution

If we chart my chosen measures on the same graph, preserving each unique y axis, we get the following:

In general, the gains and losses in (these measures of) human well-being during the pre-industrial era are miniscule compared to the gains made during the post-industrial era, and there is a sharp upward trajectory change for all these measures shortly after 1800. This provides a qualitative, as well as loosely quantitative picture of the magnitude of change I have in mind when I speak of “transformative” change.

It is worth remembering that the long-run history of human well-being could have looked quite different. It’s easy to imagine a world in which these key aspects of human well-being varied independently of each other, and fluctuated substantially up and down over time, akin to the pattern seen for GDP/cap from years 1-1800. Instead, they all run together, and they all show a single, sharp bend upward shortly after 1800.

Have there been other transitions in recorded history of comparable magnitude?

To many readers, it will not be a surprise that such a transformative change occurred shortly after the industrial revolution. What is perhaps more surprising is to consider how many major historical events seem to have not produced anything close to such a transformative change.

If we drop the y axes (for space reasons), and add other major historical events to the summary chart from the previous section, we get the following:

In short, no other transitions in recorded history are remotely comparable in their magnitude to the transition that followed the industrial revolution.

Perhaps the best contender for a transition of comparable magnitude is the agricultural revolution, but that transition predates “recorded” history, and I don’t discuss it much here because our data for human well-being during that period are so limited.

The possibility of transformative negative change

As shown above, there seems to be no precedent in recorded history for negative changes that would count as “transformative” in my rather extreme sense of the term. Nevertheless, is easy to imagine that some future catastrophe could cause a “reverse industrial revolution,” such that within a century or two (or much less) of its occurrence, human well-being was roughly what it was prior to the industrial revolution, or even worse.

Consider an extreme example: if a nearby supernova explosion destroyed all life on Earth, thereby setting all human well-being variables to zero, this would clearly qualify as an event of transformative negative impact. ⁴⁰

But short of outright human extinction, how bad would a catastrophe need to be, in order to produce a “reverse industrial revolution” or worse — that is, to have a transformative negative impact? To get a feel for this, I briefly studied the magnitude of the deadliest catastrophes in world history. ⁴¹

How many deaths might result in transformative negative change?

Which are the deadliest catastrophes in recorded history? Death toll estimates vary hugely, but my guess (see my process) is that the deadliest catastrophes in recorded history (which took place over the span of three decades or less) are: ⁴²

Catastrophe	Years (CE)	% of world population lost
Xin Dynasty	9-24	~5.3%
Plague of Justinian	541-544	~2.7%
An Lushan Rebellion	755-763	~5.6%
Genghis Khan’s conquests 43	1206-1227	~9.5%
Black Death	1345-1353	~9.7%
Thirty Years’ War	1618-1648	~1.4%
Fall of the Ming Dynasty	1635-1662	~4.6%
Taiping Rebellion	1850-1864	~1.6%
World War I	1914-1918	~0.8%
1918 flu pandemic	1918-1919	~3.3%
Joseph Stalin‘s rule	1928-1953	~1%
World War II	1939-1945	~2.9%
Mao Zedong‘s rule	1949-1976	~1.6%

It’s difficult to know what the effects of these events were, both because of the limited availability of data (especially prior to ~1700) and because the practice of counterfactual history is necessarily highly speculative in most cases. ⁴⁴ Still, we know from the charts above that none of them (including the Black Death ⁴⁵ ) seem to have been “transformative” in the sense discussed above. In fact, none of them seem to have had a lasting impact even on world population:

Here, a catastrophe like World War II — by my estimates, the deadliest event in world history (in absolute numbers) — shows up as a small kink in the upward curve, after which the previous trend continues unabated. ⁴⁶

One might suggest that some catastrophe averted a trajectory change that would have soon happened, if not for the catastrophe. Thus, one might argue, the charts we can produce from the data available to us look mostly flat until shortly after the industrial revolution, but this actually represents a major trajectory change from how they would have looked had the catastrophe not occurred. (I’ll call such a trajectory change an “invisible” trajectory change, since it does not appear as a sharp bend in the most important trend lines.)

I concede this is possible, but it seems very difficult to assess the plausibility of a proposed historical invisible trajectory change, and in general I am skeptical that any such “invisible trajectory changes” have occurred — including as a result of catastrophes that didn’t kill enough people, quickly enough, to make it on my list of deadliest catastrophes, such as the fall of the Western Roman Empire. ⁴⁷

Why? A great many things happened in human history prior to the industrial revolution, some of them seemingly momentous, and yet none of them seem to have produced a trajectory change, positive or negative, that was anywhere near the scale of the trajectory change that followed the industrial revolution. For example, suppose for a moment that the industrial revolution is, in fact, the primary cause of the trajectory changes discussed above. Historians are uncertain about (and disagree about) which factors were jointly needed to produce the industrial revolution, ⁴⁸ but they seem to agree that multiple factors were required, and this explains why the industrial revolution did not occur sooner. For example, in the Ancient Greco-Roman world, Archimedes and a few others practiced modern science (in the sense of experimentally testing predictions deduced from a precise mathematical model of some natural phenomenon), ⁴⁹ Heron invented a working steam engine, ⁵⁰ and an unknown inventor created an analogue computer capable of (among other things) adding and subtracting angular velocities, ⁵¹ yet all this did not produce an industrial revolution, presumably because some other factors were not in place. For some historical disaster to have produced an invisible trajectory change, it needs to have been the case that all the other factors required for transformative change were in place, such that transformative change would have occurred if not for the disaster. From my (admittedly limited) readings of history, I am doubtful this is the case, albeit not with strong confidence.

From the above discussion, I draw the following tentative conclusions:

• By my estimate, the deadliest event before the industrial revolution (the Black Death) killed ~9.7% of world population, and the deadliest event after the industrial revolution (the 1918 flu pandemic) killed 3.3% of world population. Alternately, we might consider World War I and the 1918 flu pandemic a “double catastrophe” ⁵² — since they occurred so close together in time and place, and the former exacerbated the latter — in which case their combined death toll was ~4.1% of world population.
• As far as I can tell from the limited available data, it doesn’t seem that any of the deadliest events in recorded history had a transformative negative impact (in my sense of “transformative”).
• As such, we don’t any historical precedents from which to estimate how many deaths might be required to produce a transformative negative impact. There is no precedent for a rapid loss of >10% of world population, and no precedent for a rapid loss of >5% of world population since the industrial revolution and the beginning of the positive trends humanity has experienced since then. ⁵³

Hence, as Nick Beckstead wrote previously:

Thus, past experience can provide little grounds for confidence that the positive trends [observed since the industrial revolution] would continue in the face of [a catastrophe of] unprecedented severity.

In this way, our situation seems analogous to the situation of someone who is caring for a sapling, has very limited experience with saplings, has no mechanistic understanding of how saplings work, and wants to ensure that nothing stops the sapling from becoming a great redwood. It would be hard for them to be confident that the sapling’s eventual long-term growth would be unaffected by unprecedented shocks — such as cutting off 40% of its branches or letting it go without water for 20% longer than it ever had before — even taken as given that such shocks wouldn’t directly/immediately result in its death. For similar reasons, it seems hard to be confident that humanity’s eventual long-term progress would be unaffected by a catastrophe that resulted in [an unprecedented number of deaths].

The question is, at what threshold of “unprecedented number of deaths” should we start to worry about transformative negative impact?

My instinct is to start with what we know from the deadliest events occurring after the industrial revolution. Perhaps the ~10% population losses produced by Genghis Khan (in the 13th century) and the Black Death (in the 14th century) do not tell us much about the plausible impact of a 10% loss of population today, because they occurred during the long, “flat” period of history dominated (in the long run, in most places) by a generally Malthusian equilibrium. ⁵⁴ Perhaps it is easier to derail and even “reverse” the sort of fast-moving, positive trajectory we’ve observed since the industrial revolution than it is to achieve a (worldwide) “escape” from a long, slow, generally Malthusian dynamic. ⁵⁵

On the other hand, even the double catastrophe of World War I and the immediately subsequent 1918 flu pandemic does not seem to have “come close” to having a transformative impact. How much deadlier than that would a catastrophe need to be, to have a serious chance of transformative impact?

Somewhat arbitrarily, I’d guess that I should start to seriously worry about the possibility of transformative impact from a loss of life (within three decades) that is ~4x as large as the double catastrophe mentioned above — i.e. a loss of 16.4% of world population. To avoid fake precision, I’ll round this to 15%. Today, this would be equal to a loss of ~1.1 billion people. ⁵⁶

Of course, transformative impact might result from a much smaller number of deaths, depending on how those deaths are distributed, and on other factors. For example, the emergence of global authoritarian rule wouldn’t need to kill a billion people in the space of a few decades to nevertheless bend the curves of human well-being enough to qualify as a “transformative” negative change.

What do these initial findings suggest about potential future transformative developments?

Overall, my initial findings lead me to the following tentative conclusions:

1. When thinking about potential negative transformative developments, we have little evidence to draw from, since there has not been a single negative change of “transformative” magnitude in recorded history. Based on my brief reasoning here, I would begin to “seriously worry” about the possibility of transformative negative impact from an event that killed ≥15% of world population. Depending on other factors, I might also seriously worry about transformative negative impact from some events which result in a much smaller number of deaths.
2. The gains in human well-being observed since the industrial revolution are vastly larger than pre-industrial fluctuations in human well-being. No other transitions in recorded history are remotely similar in magnitude.
3. Hence, when thinking about which future developments might be most important, we should not forget that the sizes of their likely impact might differ by orders of magnitude.

I will illustrate point (3) with an example. A universal cure for cancer would be a huge benefit to human well-being, but the expected benefit to U.S. life expectancy from such a cure is only 2.83 years, ⁵⁷ and the average expected benefit in the rest of the world is even lower. ⁵⁸ Presumably the impacts on economic well-being would be of roughly comparable magnitude, and the impacts on the other key aspects of well-being discussed above would be even smaller, and perhaps negligible.

In contrast, consider the magnitude of the likely impacts on human well-being from the development of AI systems capable of automating most human labor, or the counterfactual benefits of preventing large-scale nuclear war. We have no precise estimates of the likely impacts of these potential future transformative developments (if they occurred), but they are very probably vastly greater in magnitude than the likely impact of a cure for cancer.

Of course, one must consider not only a cause’s importance but also its tractability and neglectedness. Perhaps all potential future transformative developments are so intractable and/or crowded that they are not worth investing in despite their extreme importance. Or perhaps they aren’t quite so intractable or crowded. I’d like to check.

Appendix A. Other important aspects of human well-being

Above, I chose the following as “key aspects” of human well-being: subjective well-being, physical health, economic well-being, empowerment via energy capture, empowerment via technology, empowerment via political freedom, and social well-being.

No doubt some readers will think my list misses some fairly fundamental aspects of human well-being. Below, I list some additional aspects of human well-being I considered including, and I say a bit about why I didn’t include them.

• Education, e.g. as measured by rates of literacy, primary education, or higher education, or by test scores, or by measures of educational mobility. ⁵⁹ In this report, I primarily treat education as an important input to what I consider to be “more fundamental” aspects of well-being — in particular, economic well-being, technological empowerment, and empowerment via political freedom — rather than as a key aspect of well-being itself. (See footnote for an argument. ⁶⁰ ) That said, a case could certainly be made that education is an important aspect of well-being even apart from its impact on economic well-being, technological empowerment, and political freedom.
• Empowerment via personal capabilities: Education can be seen as a special case of what we might call “empowerment via personal capabilities,” which is distinct from empowerment via energy capture, technology, and political freedom, and also distinct from the features of “being in good health” captured by the measures of physical health discussed above. Measures in this category could include measures of conscientiousness, work ethic, cognitive capabilities, various manual skills, and so on. Some of these do seem pretty important to me, but I suspect they are indirectly measured fairly well by measures of economic well-being and physical health (because those with greater capabilities tend to earn more and live longer), and we have better long-run data for those measures anyway.
• Work-related well-being, e.g. as measured by job satisfaction, leisure time, and career advancement. ⁶¹ Personally, I think of work-related well-being as less fundamental than the aspects of well-being I chose to cover in this report. Work-related well-being is also partly assessed by measures of economic well-being.

Appendix B. Some methodological details

Where my death toll estimates come from

Here, I summarize how I constructed the death toll estimates used in my section on deadliest catastrophes.

Initially, I had hoped to simply pull death toll estimates from Wikipedia. Unfortunately, I found Wikipedia to be an unreliable source for death toll estimates. For example, when I checked Wikipedia on March 15, 2017:

• Wikipedia’s List of wars and anthropogenic disasters by death toll provided “lowest” and “highest” estimates for World War II of 65 million and 85 million, respectively. However, I quickly found that in Matthew White’s collection of historians’ estimates of the death toll of World War II, most estimates were lower than 55 million, with the median estimate at 50 million.
• The first sentence of Wikipedia’s Black Death article claimed a death toll of “75 to 200 million people,” citing three news articles ⁶² which themselves provide no sources for their estimates. ⁶³ Searches for academic literature ⁶⁴ turned up many academic sources using the 200 million figure, but nearly all of them (that I checked) made clear that the 200 million figure sums deaths across multiple (usually, “three”) different pandemics caused by Yersinia pestis, occurring centuries apart. ⁶⁵ Moreover, for the academic sources providing a citation for the 200 million figure that I was able to track down, ⁶⁶ the reference trail in all cases led eventually to a single source: an article from the May 1988 issue of National Geographic by photojournalist Nicole Duplaix, titled “Fleas: The Lethal Leapers” (pp. 672-694). That article, too, is clear that the 200 million figure refers not to deaths for the “Black Death” of the 1340s-50s, but to deaths summed across multiple pandemics. ⁶⁷ Moreover, this number is highly suspect, given that Duplaix provides no source or analysis for it.

Thus, I began to estimate historical death tolls myself, drawing from credible-looking scholarly primary sources wherever possible. Fortunately, I soon noticed that the estimates I came up with after a bit of research tended to closely match the estimates provided in Matthew White’s book The Great Big Book of Horrible Things: The Definitive Chronicle of History’s 100 Worst Atrocities (2011). ⁶⁸ Hence, I decided to use White’s estimates as a starting point, and then, for each estimate, I checked his reasoning and the apparent credibility of his key sources.

Unfortunately, White’s book only covers anthropogenic disasters, a category which excludes pandemics, which account for several of the deadliest catastrophes in history. Thus, I constructed pandemic death toll estimates myself.

Once I had death toll estimates, I used economist Max Roser’s annual world population data (from Roser & Ortiz-Ospina 2017a) to estimate “% of world population lost.” My calculations are here.

Below, I explain in some detail the pandemic death toll estimates I had to construct myself, for the 1918 flu pandemic, the Plague of Justinian, and the Black Death.

1918 flu pandemic
For the 1918 flu pandemic, the most credible-looking estimate of the death toll I’ve seen is Johnson & Mueller (2002), which seems to be the primary source for widely-cited estimates of “50-100 million deaths” due to these statements:

Further research has seen the consistent upward revision of the estimated global mortality of the [1918 flu] pandemic, which a 1920s calculation put in the vicinity of 21.5 million. A 1991 paper revised the mortality as being in the range 24.7–39.3 million. This paper suggests that it was of the order of 50 million. However, it must be acknowledged that even this vast figure may be substantially lower than the real toll, perhaps as much as 100 percent understated.

…

There are vast areas of the world for which we have no or little information, and often what information we do have is of dubious quality and contradictory. Sometimes the data cover only certain cities or populations; often the indigenous mortality has never been considered. Sometimes the figures given are only those that were recorded as influenza deaths; at other times, they are influenza and pneumonia deaths. Consequently, the real pandemic mortality may fall in the range of 50 to 100 million, but it would seem unlikely that a truly accurate figure can ever be calculated.

In other words, their estimate from published records is 50 million deaths (actually 48.8 million deaths; see Table 5), but they speculate that the true number may be as high as 100 million deaths.

To construct my estimate, I struck a balance between empirical estimates and speculation, relying more on the former than the latter, and (somewhat arbitrarily) guessed that the 1918 flu pandemic killed ~60 million people. (Purposely, this is substantially less than the geometric mean of 48.8 million and 100 million, which is 69.9 million.)

Plague of Justinian
Wikipedia’s article on the Plague of Justinian claims a death toll of 25-50 million “in two centuries of recurrence,” but my focus is on the first (and deadliest) wave of the plague, from 541-544. ⁶⁹

After checking many scholarly sources on the Plague of Justinian, ⁷⁰ I was not able to find a credible scholarly estimate of the death toll from 541-544. Thus, I contacted a scholar who wrote a recent review article and book on this topic, Dionysios Stathakopoulos of King’s College London, and asked how he would recommend I produce a (very rough) estimate of the death toll. Dr. Stathakopoulos suggested I could use the rough mortality rate he found plausible for Constantinople in Stathakopoulos (2004) (20%), ⁷¹ and multiply that by the rough estimate of the population of the empire at the time that he came to in Stathakopoulos (2008) (28 million). ⁷² This suggests a (very rough) death toll estimate of ~5,600,000.

Black Death
Plague in the 14th century may have arisen as early as the 1330s, and it recurred in numerous waves across multiple centuries, but for this report I’ll use “Black Death” to refer to its first (and deadliest) proven wave in the 14th century, from 1345-1353. ⁷³

I consulted several scholarly sources on the Black Death, ⁷⁴ and my impressions are that:

• The most common view seems to be that about 1/3 of Europe perished in the Black Death, starting from a population of 75-80 million. However, the range of credible-looking estimates is 25%-60%.
• The only credible-looking estimates of the death toll in the Islamic world I’ve found are from Dols (1977). For Egypt, Dols estimates a loss of 25%-33% from a starting population of 4.2-8.0 million, and for Syria he estimates a 33% loss from a starting population of 1.2 million. ⁷⁵ The Black Death also reached some other areas of the Middle East and North Africa, for example Barca in Libya and Tunis in Tunisia, but I haven’t seen any attempts to estimate the death tolls outside Egypt and Syria.
• Some sources claim large death tolls in Asia, ⁷⁶ but as far as I can tell, this is mere speculation, and not substantiated by any hard evidence to date. ⁷⁷

To generate a very rough death toll estimate for this report, I took the geometric mean of my “lowest plausible estimate” and my “highest plausible estimate.” My lowest plausible estimate is:

• For Europe, perhaps 25% of people died, from a starting population of 75 million.
• For the Middle East and North Africa, perhaps Egypt lost 25% from a starting population of 4.2 million, Syria lost 33% from a starting population of 1.2 million, and the rest of the Middle East and North Africa lost 33% from a population of (let’s say) 2 million from the most populated areas.
• In Asia, perhaps the Black Death killed almost no one.

My highest plausible estimate is:

• For Europe, perhaps 60% of people died, from a starting population of 80 million.
• For the Middle East and North Africa, perhaps Egypt lost 33% from a starting population of 8 million, Syria lost 33% from a starting population of 1.2 million, and the rest of the Middle East and North Africa lost 33% from a population of (let’s say) 6 million from the most populated areas.
• In Asia, perhaps the Black Death killed (let’s say) 15 million, even though we have no direct evidence of this.

Thus, my lowest plausible estimate adds up to 20,856,000, and my highest plausible estimate adds up to 68,016,000. The geometric mean of these two numbers is 37,666,533.

My incomplete attempt to generate worldwide slavery estimates

Above, I mention that percent of people not enslaved would be perhaps the best measure of empowerment via political freedom, if only we had the data. Below, I recount my unfinished attempt to generate highly speculative estimates of the percent of people not enslaved over time.

Shifting impressions

While studying the history of slavery, my impression of how well the curve for “percent of people not enslaved” would mirror those charted above flipped back and forth multiple times.

The first related dataset I encountered was Steven Pinker’s chart of number of political states to abolish slavery over time, which is figure 4-6 in Pinker (2011). ⁷⁸

In brief: Iceland was the first state to abolish slavery, in 1117. But progress on abolition continued to be extremely slow until about 1775, during the industrial revolution. Then, the number of states abolishing slavery rose quickly up to 1981, when Mauritania became the last country on Earth to abolish slavery. Unfortunately, slavery continues (illegally) in several countries, but the proportion of people enslaved during the past few decades is probably lower than at any other time in recorded history. ⁷⁹

At first glance, Pinker’s chart seemed to mirror the combined chart above surprisingly well. However, I quickly grew suspicious of this initial judgment. First, the inflection point in Pinker’s chart appears early in the industrial revolution rather than after 1800. Second, my guess was that by the time a political jurisdiction abolished slavery, it was probably already a fairly unpopular practice in that jurisdiction anyway — suggesting that if we could chart “proportion of world population enslaved” over time, the trajectory change would appear long before the industrial revolution. One of the first histories of slavery I read seemed to confirm this (Payne 2004, ch. 13):

Serfdom as an alternative to slavery began to appear in Italy in the late years of the Roman Empire (a.d. 400– 500)… In France, serfdom had almost entirely replaced slavery by around 1200. In England, slavery rapidly disappeared after the Norman Conquest of 1066. Up until that time, slavery was common, with approximately 10 percent of the population being slaves. The Norman invaders, who considered France their home, freed slaves on the English estates they took over and made them serfs “to avoid the necessity of close supervision and management of slaves.” The economic pressures against slavery meant that this practice had largely died out in Europe by the late Middle Ages. It had also faded away in other places as well. In Japan, for example, it had become rare by the year 1200.

Thus, I concluded that slavery’s primary trajectory change probably came long before the industrial revolution.

However, as I continued to study the history of slavery, I learned several things that made me wonder once again whether slavery’s primary trajectory change actually did coincide quite well with the other trajectory changes charted above.

1. Actually, slavery was still quite popular in most jurisdictions at the time it was abolished; northern Europe seems to have been the exception here, not the rule. ⁸⁰
2. Even as slavery declined (in favor of serfdom) in northern Europe during the medieval period, it flourished and perhaps even grew in the Islamic world and perhaps elsewhere. Hence “proportion of world population enslaved” might not have declined much during the medieval period. ⁸¹

3. Arguably, many forms of serfdom ought to be counted as not very different than slavery from a “political freedom” perspective; if so, then perhaps political freedom in this sense did not increase much during the medieval period, even in Europe.
4. The global antislavery movement more-or-less began with the British abolitionists, circa 1800-1840 — suspiciously, right at the end of the industrial revolution, in the home country of the industrial revolution. Britain was thereafter the primary global exporter of antislavery, sailing around the world and pressuring countries all across Africa and Asia to abolish the slave trade and slavery in general. Most slavery abolition around the world seems not to have been “home-grown” (as in Britain and the USA), but in fact was exported by Britain and (later) some other European states to their colonies and the rest of the world. ⁸²

Unfortunately, I could not afford the time to resolve the question. In the absence of an initial estimate for “percent of people not enslaved” over time, I instead list the major sources I consulted, and explain my unfinished spreadsheet of regional slavery estimates.

General sources on the history of slavery

The relatively general sources on the history of slavery I consulted were: ⁸³

• Patterson, Slavery and Social Death (1982)
• Davis, Slavery and Human Progress (1984)
• Rodriguez, Chronology of World Slavery (1999)
• Campbell (ed.), Structure of Slavery in Indian Ocean Africa and Asia (2003)
• Payne, A History of Force (2004), ch. 13
• Campbell (ed.), Abolition and its Aftermath in Indian Ocean Africa and Asia (2005)
• Hinks & McKivigan (eds.), Encyclopedia of Antislavery and Abolition (2006), in particular the entries categorized under “Antislavery and Abolition in Specific Countries and Regions” in the “Guide to Related Topics,” plus the entries on “Classical Greek Antislavery,” “Classical Rome and Antislavery,” and “Slavery and Abolition in the Twentieth Century”
• Davis, Inhuman Bondage (2006)
• Grayling, Toward the Light of Liberty (2007)
• Campbell et al. (eds.), Women and Slavery, Volume One (2007)
• Walvin, A Short History of Slavery (2007)
• Dal Lago & Katsari (eds.), Slave Systems: Ancient and Modern (2008)
• Drescher, Abolition: A History of Slavery and Antislavery (2009)
• Bradley & Cartledge (eds.), The Cambridge World History of Slavery, Volume 1: The Ancient Mediterranean World (2011)
• Bodley, Cultural Anthropology: Tribes, States, and the Global System, 5th edition (2011), ch. 5, for its discussion of slavery in tribal societies (drawing from Gray 1999)
• Heuman & Burnard (eds.), The Routledge History of Slavery (2011)
• Hunt, “Slavery” (2015)

Some especially informative “overview” passages from some of these sources are provided in a footnote. ⁸⁴

How I built my slavery spreadsheet

My plan for constructing an initial (and highly speculative) estimate of “percent of people not enslaved” over time was the following:

1. Collect every scholarly estimate I could find for the proportion of people enslaved in a given region during a given time.
2. Combine those estimates with a database of estimates for the total population of different regions at different times.
3. For the region × time interval cells for which I didn’t have a “percent enslaved” estimate (the vast majority of all cells), simply guess that the rate of slavery then and there may have been similar to that of the most similar time and place for which I do have a “percent enslaved” estimate. When making these guesses, prioritize making guesses for the most populous areas (at a given time).
4. Once I have gathered estimates or guesses for regions accounting for (say) 40% of global population at each time interval, make broader, quicker guesses for the rates of slavery in the remaining regions.
5. Use these estimates and guesses to calculate an initial guess for “percent enslaved” at each time interval.
6. Show the resulting curve and spreadsheet to experts in the world history of slavery, and learn which guesses they most strongly disagree with, and adjust accordingly.

Naturally, the resulting curve would be extremely speculative, but it might qualify as “the best guess I could make, if I had to guess.”

I collected many slavery and population estimates in a spreadsheet here, but I did not come close to executing the full plan.

Footnotes:

1. There are other ways to look for opportunities to accomplish as much good as possible, of course, and the Open Philanthropy Project pursues some of them; see the blog post on worldview diversification. For more on the potential value of the sorts of “trajectory changes” discussed in this report, see Beckstead (2013), ch. 3.

   I would also like to examine which future developments might have the largest impact on the future well-being of non-human moral patients, but for simplicity, I discuss only human well-being on this page.[↩]

2. I paraphrase this summary from comments made by the Open Philanthropy Project’s Managing Director Holden Karnofsky, who shared his impressions of the plausible impact of the Green Revolution at an Open Philanthropy Project research event held on June 6, 2017 (starting around 4:10 in the recording available here):

   …the Rockefeller Foundation funded [an] improved agricultural approach that [some] people have credited with kickstarting the East Asian tigers development phenomenon, getting a lot of countries to go from poor to middle income, turning India from being in the middle of famine to being a wheat exporter, saving over a billion people from starvation, and resulting in a Nobel peace prize for Norman Bolaug… [This is] maybe one of the most significant humanitarian developments of the last century — or really, ever.

   The causal impacts of the Green Revolution in general, and the Rockefeller Foundation’s funding in particular, are of course difficult to discern with any certainty, and I don’t discuss the evidence for these specific claims here. Some sources that contributed to Karnofsky’s impressions on this topic include those linked from Can the Green Revolution be repeated in Africa?[↩]

3. Holden Karnofsky introduced this use of the term “transformative” when he defined “transformative artificial intelligence” (transformative AI), roughly and conceptually, as “AI that precipitates a transition comparable to (or more significant than) the agricultural or industrial revolution.”[↩]
4. This terminology isn’t ideal, though — in part because most people use the term “transformative” to refer to much smaller changes than the changes I label “transformative” here. Perhaps someone else will suggest a better term.[↩]
5. Open Phil thinks transformative AI is one such potentially transformative development. See here for a summary of some earlier thinking about additional potentially transformative developments.[↩]
6. See this footnote.[↩]
7. For an overview, see Allen (2017).[↩]
8. Economic historians, at least, tend to think that the industrial revolution is the most transformative event in human history — at least since the Neolithic revolution (c. 10,000 BCE) — though they don’t necessarily address the industrial revolution’s impact on the particular measures I discuss in this report.

   For example, McCloskey (2004):

   [The industrial revolution] is certainly the most important event in the history of humanity since the domestication of animals and plants, perhaps the most important since the invention of language.

   Clark (2014):

   The Industrial Revolution decisively changed economywide productivity growth rates. For successful economies, measured efficiency growth rates increased from close to zero to close to 1% per year in the blink of an eye, in terms of the long history of humanity…

   Around 1780 came the Industrial Revolution in England. Incomes per capita began a sustained growth in a favored group of countries around 1820. In the last 200 years, in the most fortunate countries, real incomes per capita rose 10–15-fold. The modern world was born. The Industrial Revolution thus represents the single great event of world economic history, the change between two fundamentally different economic systems…

   The Industrial Revolution thus seems to represent a singularity. A unique break in world history.

   Lucas (2002) opens his chapter on the industrial revolution this way:

   From the earliest historical times until around the beginning of the nineteenth century, the number of people in the world and the volume of goods and services they produced grew at roughly equal, slowly increasing rates… Then, during the last 200 years, both production and population growth have accelerated dramatically, and production has begun to grow much more rapidly than population. For the first time in history, the living standards of masses of ordinary people have begun to undergo sustained growth. The novelty of the discovery that a human society has this potential for generating sustained improvement in the material aspects of the lives of all of its members, not just of a ruling elite, cannot be overstressed. We have entered an entirely new phase in our economic history.

   van Leuss (2015) writes:

   The industrial revolution, which started in Britain before sweeping through Europe and the USA, is traditionally viewed as the deepest mutation ever known to have affected men since Neolithic times. As Cipolla (1975:7) contended: ‘Between 1780 and 1850, in less than three generations, a far-reaching revolution, without precedent in the history of Mankind, changed the face of England. From then on, the world was no longer the same. Historians have often used and abused the word revolution to mean a radical change, but no revolution has been as dramatically revolutionary as the Industrial Revolution, except perhaps the Neolithic Revolution.'”

   Economic historians disagree, however, on just how gradual or discontinuous these changes were. E.g. see ch. 1 of Mokyr (2011); Berg & Hudson (1992); Broadberry (2015); Goldstone (2015); van Neuss (2015).

   Personally, I find it plausible that the industrial revolution is the primary cause of most or all of the trajectory changes I discuss in this section, though I’m not sure whether I should think this is “probable.”

   If this conjecture is true, why did most of the trajectory changes discussed on this page not occur until several decades after the close of the industrial revolution? Part of the explanation may be that it took a while for industrialization to spread beyond Britain and Western Europe. (An especially useful source on the spread of modern industry around the world is O’Rourke & Williamson 2017, in particular chapter 2 by Bénétrix et al.; data here.) Another part of the explanation may be that in each region (including Britain), it usually took a few (or several) decades for industrialization to translate into higher well-being (of various sorts) for the populace at large.

   [↩]

9. Of course, knowing something about the causes of the trajectory changes discussed in this section could help one better predict which future events might be capable of producing trajectory changes of similar magnitude, but studying the causes of historical trajectory changes is beyond the scope of this report.[↩]
10. For an overview of attempts to construct philosophically precise theories of well-being, see Crisp (2013); various chapters in Fletcher (2015); Dowding (2009). For overviews of measures of well-being used in large-scale national and international surveys of well-being, see Glatzer et al. (2015); Sirgy et al. (2017); Roser (2017).[↩]
11. I don’t mean to suggest these aspects of empowerment are independent, of course. Technology makes higher energy use possible, political freedom probably enables greater numbers of people to contribute substantively to the development of new knowledge and technology, etc. The other aspects of well-being I discuss (besides empowerment) are also not independent.[↩]
12. Cicognani (2014) provides a short overview of measures of social well-being. On trust specifically, see the Trust entry from Our World in Data.

    For introductions to the research on subjective well-being, see e.g. Roser (2017); OECD (2013); Helliwell et al. (2017). Note that unlike many measures used in high-stakes educational testing and for patient-reported outcomes in health care, self-report measures of subjective well-being (and other self-reported variables mentioned but not used in this report) typically have not been validated using modern test theory (e.g. IRT), which may be especially important for making meaningful comparisons of scores between cultures and across long spans of time (see notes from my conversation with Louis Tay).

    If we possessed a measure of subjective well-being that had reasonable validity between cultures and across long spans of time, and we had data collected using that measure going back many centuries and spanning many cultures, would the curve of subjective well-being over time look similar to the curves observed for most measures discussed in this appendix, with little change observed for many centuries and a sharp upward spike shortly after the industrial revolution?

    I think it’s hard to say. On the one hand, people who live today in objective circumstances similar to those of most people living before the industrial revolution tend to score far below the median on the measures of subjective well-being used today (Roser 2017; Sacks et al. 2013). On the other hand, hedonic adaptation is a powerful force (Luhmann et al. 2012; Yap et al. 2014), and perhaps most people of the past were hedonically adapted to their circumstances. In part, one’s views on this question might be predicted by one’s position in debates over the “Easterlin paradox” (e.g. Sacks et al. 2013 vs. Easterlin 2015).[↩]

13. Van den Berg (2016), referring to data from several sources, provides the following brief summary (sec. 2.3.1):

    10,000 years ago in the primitive hunter-gatherer societies, about half of all children died before reaching the age of five. As late as the 1500s, one quarter to one-third of all children died before reaching the age of five in countries that are highly developed today, such as England, Sweden, and Switzerland. Very few countries have infant mortality rates over 100 per thousand births today. Overall, worldwide infant mortality is about 50 per 1,000 births, one-tenth the level of the pre-agricultural world before 10,000 BCE and one-fifth the level in the most advanced countries just 200 years ago.

    Life expectancy was between 20 and 30 years from prehistoric times until about 1500. For example, George Acsadi and J. Nemeskeri (1970) used skeletal remains from northern Egypt to conclude that during the Neolithic period (6,000-3,000 BCE), life expectancy at birth was 21 years. John Hatcher’s (1986) data on the lives of Benedictine monks in Canterbury, England during the period 1395–1505 shows that their average life expectancy was just 22 years. In the mid-1700s, life expectancy in London was still just 25 years.

    After virtually no improvement for thousands of years, suddenly, after about 1750 or 1800, life expectancy grew rapidly. It tripled over the past 200 years. You should be able to envision a diagram of life expectancy… consisting of a horizontal path stretching over thousands of years and then, suddenly, shooting up during the last two centuries.

    Roughly in keeping with this account, and with Roser’s claim that “in a pre-modern, poor world, life expectancy was around 30 years in all regions of the world,” every source I’ve seen gives regional life expectancy estimates for the ancient and medieval world that are below 45, and often much lower than that. Below are some examples:

    • Zhang (1991) claims that life expectancy in ancient China “ranged from 22 to 35.”
    • Hsiung (2005) claims that life expectancy in late imperial China was “between thirty and forty years” (pp. 156-157), but elsewhere suggests it was “approximately in the upper thirties and lower forties for males and females” (p. 165).
    • In the opening chapter of Liu et al. (2001), John C. Caldwell writes (p. 8) that “The estimation of Asian mortality before 1850 has hardly begun. The only earlier information in this book is that derived by Campbell from the Qing lineages. These show a joint male-female expectation of life at birth of 26 years for 1644-1739, 32 years for 1740-1839 and 33 years for 1840-1899, averaging life expectancies for the two sexes for the first period, and assuming a similar male-female gap for the next two periods.”
    • Coale (1986), p. 23, estimates life exepctancy in Europe prior to Europe’s demographic transition (in the late 18th century) at 20-35 years. However, this estimate is not based on anthropometric observations, but from reasoning about what fertility and mortality rates must have been to maintain relatively stable population numbers over a long period of time.
    • Drawing on many sources, Lee & Feng (1999) conclude that in China, for some “300 years prior to the mid-twentieth century, male life expectancy at birth remained somewhere between the high 20s and the low 30s.”

    [↩]

14. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
15. Scheidel (2012) explains:
    

    Body height is an important marker of physical wellbeing. Human growth is sustained by net nutrition, which is determined not only by food intake but also by energy-consuming activities such as work and by infections that mobilize immune responses or interfere with the processing of the diet. If net nutrition is inadequate for any of these reasons, the body prioritizes survival over growth. While growth may catch up if such stresses remain episodic, chronic net malnutrition inevitably results in stunting, an outcome that may also be caused by acute but severe deprivation. This permits us to view adult stature as a generic index of well-being in childhood and adolescence.

    For reviews of studies on height as a proxy measure for health and other well-being variables, see Steckel (1995, 2009).[↩]

16. I do, however, make a speculative guess about the long-run trend in my spreadsheet of long-run trends in human well-being, which also provides some explanation of that guess, and cites several sources estimating regional adult height trends, in some cases stretching back to ancient times.[↩]
17. For example, consider life expectancy vs. homicide: to me, it seems intuitive that the difference between dying at age 45 vs. 75 is more important to one’s well-being than the difference between dying at age 45 of homicide and dying at age 45 of an infectious disease.[↩]
18. nef (2009), p. 21.[↩]
19. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
20. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
21. As with several other measures discussed in this report, the trajectory change in GDP per capita came sooner in countries that industrialized earlier, as shown here in a chart of real GDP per capita (PPP adjusted, i.e. adjusted for cost of living) with separate lines for UK, USA, China, India, and the world average:

    

    [↩]

22. Roser & Ortiz-Ospina (2017b):

    The available long-run evidence shows that in the past, only a small elite enjoyed living conditions that would not be described as ‘extreme poverty’ today. But with the onset of industrialization and rising productivity, the share of people living in extreme poverty started to decrease. Accordingly, the share of people in extreme poverty has decreased continuously over the course of the last two centuries. This is surely one of the most remarkable achievements of humankind.

    [↩]

23. To create this dataset, Roser combined data from the World Bank’s PovcalNet with data from Bourguignon & Morrisson (2002).[↩]
24. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
25. For overviews of some studies on this topic, see Clark et al. (2008); Layard et al. (2010); Clark & D’Ambrosio (2015); ch. 10 of Weimann et al. (2015); Clark (2017).[↩]
26. As far as I can tell, global income inequality was fairly flat for many centuries (since everyone was very poor, and almost no one was rich), then rose sharply as some countries became rich for the first time starting after 1800, and is now falling as China and other countries “catch up.”[↩]
27. For an overview of some more limited data that are available, see Our World in Data‘s entries on Income Inequality, Incomes across the Distribution, and Global Economic Inequality.[↩]
28. See van Leeuwen & Maas (2010); Heckman & Mosso (2014); Crawford et al. (2011).[↩]
29. Morris (2013) uses the term “social development” instead of “empowerment,” but he means roughly the same thing I mean by empowerment. In chapter 1 he writes:

    Social development, as I use the expression, is a measure of communities’ abilities to get things done in the world… Putting matters more formally, social development is the bundle of technological, subsistence, organizational, and cultural accomplishments through which people feed, clothe, house, and reproduce themselves, explain the world around them, resolve disputes within their communities, extend their power at the expense of other communities, and defend themselves against others’ attempts to extend power.

    [↩]

30. Morris (2013), ch. 3.[↩]
31. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
32. Morris (2013), p. 173.[↩]
33. Morris (2013), pp. 175-177:

    Comparisons of war-making capacity must come down to measuring the destructive power available to societies. By “destructive power” I mean the number of fighters they can field, modified by the range and force of their weapons, the mass and speed with which they can deploy them, their defensive power, and their logistical capabilities. Moreover, these basic facts — which are reasonably well documented for many times and places — must be combined with estimates of less well documented but equally important factors, such as morale, leadership, command and control, clear understanding of strategic, operational, and tactical principles, and organizational learning ability, as well as the broader parameters of the economy, logistics, ideology, and politics.

    The technical problems are daunting, but since the late nineteenth century war gamers (both military professionals and amateurs) have been struggling to find ways to reduce the bewildering complexity of reality to numerical values that can be compared…

    Some game systems come in multiple versions, simulating fighting in different times and places, providing an excellent starting point for thinking about war-making capacity across time and space. The GMT Games series Great Battles of History, for example, includes variants for second-millennium BCE chariot battles in Southwest Asia, the Roman Republic’s wars in the third and second centuries BCE, battles in India in the same period, and thirteenth-century CE Mongol battles. At the tactical level, at least, it allows thought-provoking comparisons — although, like any such system of rules, its greatest value may lie in the questions it raises when the system seems not to work well.

    In principle, the transhistorical comparisons required by the social development index should be no different from comparison of actual historical contexts, but in practice the sheer scale of change over time — and the fact that so-called revolutions in military affairs are often designed explicitly to produce war-making systems that are simply incomparable with earlier systems — vastly complicates matters. The most famous example is HMS Dreadnought, the massively armed and armored battleship introduced by Britain in 1906 with the aim of rendering all previous warships obsolete — only for naval tactics to evolve to fit this new weapon into a system in which older kinds of warships remained important.

    The same is true even of the deadliest modern weapons of all, nuclear arms. Nuclear weapons are far more destructive than non-nuclear weapons, but they are not incomparably more destructive. The very fact that the force of nuclear weapons is measured in kilotons and megatons — thousands/ millions of tons of TNT equivalent — illustrates this.

    The destructive power of nuclear-armed states dwarfs anything in earlier history. In three years of bombing, 1942-45, the U.S. Eighth Air Force dropped 700,000 tons of TNT on Germany; on Halloween 1961, the Soviet Union tested a single bomb… with a yield equivalent to 50– 57 million tons of TNT. By 1966 a single Soviet SS-9 Model 2 missile could carry a warhead equivalent to 25 million tons of TNT, more than thirty times the destructive power of all the bombs the United States dropped on Germany in World War II; and by the 1970s the Soviet Union had deployed 255 of these ICBMs.

    Nevertheless, the destructive force of nuclear weapons does remain measurable on the same scales as conventional weapons, just as the poisoning effects of radioactive fallout can be measured in rads and compared with the smaller poisoning effects of chemical and biological weapons. And like the dreadnought-class battleships built after 1906, nuclear weapons have been fitted into broader war-making systems that continue to rely on weapon types (albeit in much more effective forms) that were in use before 1945…

    The biggest difficulty that the index of social development has in measuring war-making capacity is in quantifying the relationship between the armed forces of 2000 CE and those of earlier periods. The leap in capacity between 1900 and 2000 was so enormous that it is difficult to measure, and similar difficulties, though on a less enormous scale, also apply to the leap between 1800 and 1900.

    On the one hand, this means that if we assign the maximum 250 points on the scoring system to the West in 2000, there will be a wide margin of error in percentage terms in estimates of war-making capacity in 1900, let alone in 1800 or any earlier period. On the other hand, because the gulf between modern destructive power and that in earlier periods is so enormous, the pre-1800 CE scores will be tiny, meaning that in terms of actual points on the social development index the margins of error will also be tiny. As we will see, the answers that I offer to these questions mean that no war-making system before 1600 CE merits even 0.2 points (i.e., less than one one-thousandth of the contemporary score), and very few before 1500 CE even reached 0.1 points… The main contribution that measuring war-making capacity makes to the social development index is to underline the vast gulf separating industrialized twentieth- and twenty-first-century societies from all previous societies.

    For further details of how Morris assigned his scores to different civilizational cores at different points in history, see the rest of chapter 5.[↩]

34. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
35. Roughly-speaking, of course. As with the other measures discussed in this section, my guess is that the trajectory change in war-making capacity occurred a few decades after the close of the industrial revolution.[↩]
36. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being.[↩]
37. See e.g. Wikipedia’s “Dates by country” section in its Universal suffrage article.[↩]
38. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being. For the HighCharts source, see this JSFiddle (backup here).[↩]
39. Image is licensed under a Creative Commons Attribution-Noncommercial-ShareAlike 3.0 United States License. For data, explanations, and sources, see my spreadsheet of long-run trends in human well-being, including its ‘Events’ worksheet. For the HighCharts source, see this JSFiddle (backup here). For estimated death tolls, see below.[↩]
40. For a high-level conceptual discussion of ideas similar to this notion of “transformative negative impact,” see Bostrom (2013).[↩]
41. In some ways, the analysis I undertake here is similar in spirit to a series of studies the RAND Corporation undertook in the 1960s to estimate the likely long-term impacts of thermonuclear war, in part via analysis of earlier catastrophes such as thermonuclear war. See especially Hirshleifer (1963, 1966).[↩]
42. Here, I list only catastrophes that (by my estimate; see my calculations) seem to have killed 1% of the world’s population or more. The exception is that I include World War I, because if I did not, I expect readers would wonder why it hadn’t made the list.[↩]
43. The Mongol conquests continued after Genghis Khan’s death in 1227, and thus accumulated more deaths, but these deaths are harder for me to estimate (since White doesn’t try to estimate them), and also their inclusion would make the time span of this “event” cover nearly an entire century, which would reduce its comparability with other deadly catastrophes.[↩]
44. For interesting discussions of counterfactual history, see e.g. Tetlock & Belkin (1996); Ferguson (1997); Bunzl (2004); Tetlock et al. (2006); King & Zeng (2007); Nolan (2013); Sunstein (2016); Brenton (2017).[↩]
45. Perhaps the most common argument I’ve encountered for any of history’s deadliest events being trajectory-changing is this: perhaps the Black Death led to some structural changes, which enabled the Renaissance, which led to the Scientific Revolution, which led to the industrial revolution, which was trajectory-changing. This seems possible, but it is also a very long chain of speculation that I find hard to see as a “strong” case that the Black Death was trajectory-changing. Some key sources arguing for and against this hypothesis (or something similar) are Bowsky (1971); Herlihy (1997); Epstein (2000); Cantor (2001); Benedictow (2004), ch. 34; Noymer (2007); Pamuk (2007); Van Zanden (2009).[↩]
46. One reason that earlier catastrophes like the conquests of Genghis Khan and the Black Death aren’t noticeable in this chart is because the annual world population data from which it is generated (Roser and Ortiz-Ospina 2017a) is interpolated from relatively sparse historical estimates. However, it is still the case that historians agree that world population didn’t change much from (say) 1200-1700, and that huge losses from the conquests of Genghis Khan, the Black Death, or other catastrophes were typically recovered within a few decades. Hence, if we had accurate world population data for every year going back to 10,000 BCE, the resulting chart might show noticeable “kinks” representing major catastrophes like the conquests of Genghis Khan and the Black Death, but the overall trend would look much the same.[↩]
47. Some other candidates for “greatest catastrophe that didn’t kill enough people, quickly enough, to make it on my list of deadliest catastrophes” might be:
    • The European conquest of the Americas (especially the resulting spread of European diseases), though these deaths accumulated over centuries, and estimates of the size of the pre-Columbian population vary hugely (Lord 1997; Denevan 1992; Henige 1998).
    • The precipitous decline of Muslim science following the Mongol sack of Baghdad in 1258.
    • The precipitous decline of Hellenistic science beginning in the 1st century BCE (Russo 2004, ch. 8).
    • The conflicts of the Three Kingdoms period in China.

    Concerning the fall of the Western Roman empire, recent sources which emphasize a “decline and fall” narrative include: McCormick (2001); Ward-Perkins (2005); Heather (2005); Jongman (2007); Halsall (2007); Goldsworthy (2009); Kelly (2009); Morris (2010); Scheidel (forthcoming).

    Morris (2010), p. 670, claims:

    Since the 1960s many Roman historians have rejected “decline-and-fall” theories of late Roman history… but more recently historians and archaeologists… have insisted — as I do here — on the fall in social development after 200 CE.

    Personally, I suspect the “decline and fall” story is right, but even the disaster that is the fall of the Western Roman Empire does not seem to have come close to being “transformative” in the sense I use the term in this report. For example, in another footnote I point out that, before the industrial revolution, average incomes seem to have fluctuated between subsistence level and three times that level, even at the height of the Roman Empire (according to Jongman 2007).

    Similarly, consider the evidence available to us about the physical well-being of citizens of the Roman empire vs. those who came before and after them, reviewed in Scheidel (2012):

    Evidence of longevity, health, and nutritional status is difficult to interpret because of the entanglement of economic, ecological, and cultural factors such as income, disease load, and dietary and breastfeeding practices…

    Nevertheless, anthropometry sheds light on overall levels of physical well-being which, even if they defy comprehensive explication, provide a basis for comparative assessments both within the Roman world and with other periods. It appears that the imperial economy did not generally enhance biological living standards. Physical well-being was unevenly distributed, with more benefits accruing to peripheral areas than to the core…

    …For all we can tell, just like other pre-modern economies, the economy of the Roman Empire failed to deliver noticeably longer lives and better bodies to its subjects…

    [↩]

48. Presumably, they also disagree about which factors would be jointly necessary to produce another trajectory change of that magnitude. For an overview of theories about causes of the industrial revolution, see van Neuss (2015).[↩]
49. By “modern science,” I mean something like Russo (2004)‘s definition (p. 17):

    To reach our definition of science, we start by observing that some theories that everyone regards as scientific, like thermodynamics, Euclidean geometry, and probability theory, share the following essential features:

    1. Their statements are not about concrete objects, but about specific theoretical entities. For example, Euclidean geometry makes statements about angles or segments, and thermodynamics about the temperature or entropy of a system, but in nature there is no angle, segment, temperature or entropy.

    2. The theory has a rigorously deductive structure; it consists of a few fundamental statements (called axioms, postulates, or principles) about its own theoretical entities, and it gives a unified and universally accepted means for deducing from them an infinite number of consequences. In other words, the theory provides general methods for solving an unlimited number of problems. Such problems, posable within the scope of the theory, are in reality “”exercises”,” in the sense that there is general agreement among specialists on the methods of solving them and of checking the correctness of the solutions. The fundamental methods are proofs and calculation. The “truth” of scientific statements is therefore guaranteed in this sense.

    3. Applications to the real world are based on correspondence rules between the entities of the theory and concrete objects. Unlike the internal assertions of the theory, the correspondence rules carry no absolute guarantee. The fundamental method for checking their validity— — which is to say, the applicability of the theory— — is the experimental method. In any case, the range of validity of the correspondence rules is always limited.

    Any theory with these three characteristics will be called a scientific theory.

    By this strict definition, the vast majority of ancient historical figures who are sometimes counted as “scientists” — e.g. Aristotle and Galen — do not qualify as such. However, Archimedes and a few other ancient scientists do seem to qualify as having practiced science of this “modern” kind, as Russo shows (e.g. see his discussion of Archimedian hydrostatics beginning on p. 73).

    That said, Russo does admit at least one potentially important difference between Hellenstic science and post-Gallileo science (p. 196):

    …a concept long considered essential to modern science was absent in Hellenistic science, namely the “crucial experiment.” If by that expression we understand an experiment designed for choosing between two alternative hypotheses on a particular phenomenon, then crucial experiments are present in ancient science: the nerve section practiced by Herophilus to decide if it was a motor or a sensorial nerve is an example of this type. But crucial experiments in the sense of something decisive for establishing the truth of a whole theory are certainly absent.

    [↩]

50. E.g. see Russo (2004), pp. 126-128:

    Heron describes two steam engines: a demonstration model (the eolipile, an enclosed round vessel with curved vents through which steam came out, causing it to revolve…), and a device used to open the doors of a temple when a fire was lit. Heron’s steam engines have generally been considered oddities built just to amaze, but if we consider their construction in the framework of a civilization that had started to employ water power, they can be seen instead as arising from a search for energy sources that do not depend on geographical accident…

    It should be stressed that modern steam engines are not at all, as is often implicitly assumed, an invention independent of the Hellenistic engines; there is a continuous line of descent. Heron’s expositions were studied carefully by Leonardo da Vinci, among others. The possibility of using steam as a source of power was then mooted by Giambattista della Porta in his Pneumaticorum libri tres (1601), based on Heron’s Pneumatica. The first steam engine actually built in modern times seems to have been the one described in 1615 by Salomon de Caus; it operated an ornamental fountain intermittently. Thus the inheritance from Heron was so complete that it even concerned the end to which the machine was put. Heronian technology hung on for another century in various hands, until it became economically convenient to start building steam engines for industrial use— — which is to say, when the rapidly growing energy needs of nascent industrialization no longer could be met by watermills alone.

    Here is a drawing of Heron’s eolipile:

    

    [↩]

51. I refer to the famous Antikythera mechanism. Here is Russo (2004)‘s brief description (pp. 128-130):

    In 1902, near the wreck of a ship that foundered by the islet of Antikythera, between the Peloponnesus and Crete, divers found some corroded bronze fragments that at first appeared to belong to some clock-like object with complicated gears. The find dates from the early first century B.C.…

    The partially readable inscriptions on the fragments make it clear that the mechanism has to do with the motions of the sun and the moon. According to Price’s reconstruction, it was a sort of perpetual calendar, allowing the calculation of the phases of the moon, past and future. To this end a gear train converted the motion of a wheel representing the solar cycle to another representing the sidereal revolution of the moon, according to the ratio of 254 lunar revolutions to 19 solar years.

    Technologically speaking two features stand out. One is the complexity of the mechanism, which uses at least thirty gears. This intricacy is what makes one instinctively assign the machine to the category of clockwork. The second and most remarkable feature is the presence of a differential turntable, a mechanism that allows the addition or subtraction of angular velocities. The differential was used to compute the synodic lunar cycle (moon phase cycle), by subtracting the effects of the sun’s movement from those of the sidereal lunar movement.

    Price’s verdict about the significance of the Antikythera mechanism is revealing: “We must suppose that from both Heron and Vitruvius we underestimate what was available in gearing technology in their times.” Indeed, he felt that the existence of this single object of “high technology” is enough to radically alter our ideas about classical civilization and lay to rest once and for all old clichés to the effect that the Greeks scorned technology and that the easy availability of slave labor led to an unsurmountable gap between theory and experimental and applied sciences.

    Here is a drawing of the mechanism’s apparent gear scheme:

    

    [↩]

52. For more on possible “double catastrophes” — or more generally, “compound catastrophes” — see e.g. Tonn & MacGregor (2009); Carpenter & Bishop (2009); Baum et al. (2013).[↩]
53. On these “positive trends,” see e.g. The long-term significance of reducing global catastrophic risks; Pinker (2011); Shermer (2015); Norberg (2016); Our World in Data.[↩]
54. See e.g. Jongman (2007):

    So what are we left with for pre-industrial history? Was it all one longue durée of life at or near subsistence? The answer is that it was not. Pre-industrial per capita incomes could be quite different between regions and periods, from near-subsistence to about three times subsistence (anything better had to wait until after the Industrial Revolution). The classic explanation for the differences is in the land-labour ratio. When population increased, more and more people had to work smaller and smaller plots of land. This intensive cultivation improved the productivity of the land, but at the expense of labour productivity and, therefore, labour incomes. Thus, population and popular prosperity always moved in opposite directions. Periods of population pressure witnessed a declining standard of living for labour, increased rents and elite incomes, and therefore, greater social inequality. An epidemic such as the Black Death of the middle of the fourteenth century was a blessing in disguise for the survivors. This is the bleak Malthusian scenario, in which real economic growth does not exist: increased aggregate production under population pressure cannot qualify as real growth since it is at the expense of per capita incomes. Conversely, it would be equally perverse to think of improved per capita incomes in the wake of demographic decline as economic growth. To qualify as real economic growth, both population and per capita incomes (and thus even more so aggregate income) must move in the same direction, and for a lengthy period of time. Did this ever happen before the Industrial Revolution?

    …It is my contention that Rome in the late Republic and early Empire was one of those rare examples of real pre-industrial economic growth (others would be the Dutch Republic and England in the centuries just before the Industrial Revolution).

    Note that even though Jongman emphasizes the existence of a few exceptions to the normal Malthusian equilibrium, he concedes that these exceptions were “rare,” local, and never amounted to average incomes above “about three times subsistence” until after the industrial revolution.

    See also e.g. Clark (2007), ch. 1.[↩]

55. Here, I mean “escape” in either a positive or negative direction, e.g. via an industrial revolution or a return to pre-Neolithic Revolution dynamics (or even human extinction).[↩]
56. Ideally, this figure should be adjusted to account for the underlying growth rate of world population. Just prior to World War I, the annual growth rate of world population was ~0.5% and rising, whereas today it is ~1.2% and falling (see section 1.1 of Roser & Ortiz-Ospina 2017a). However, because (1) I am especially interested in potentially transformative developments which might occur in the next 30 years, and (2) the United Nations projects that “by default” the annual growth rate for world population over the next 30 years will likely be in the range of 1.2%-0.7% (see again section 1.1 of Roser & Ortiz-Ospina 2017a), and (3) that range of growth rates is not hugely different from the annual growth rate in the period shortly before (or especially, immediately after) the “double catastrophe” of World War I plus the 1918 flu pandemic, and (4) my estimates in this section incorporate so much guesswork anyway, I decided for simplicity to stick with the “15% of world population” figure for the purposes of this section.[↩]
57. The most recent U.S. estimates I’m aware of are from 2008, reported in Wang et al. (2013), table 2.[↩]
58. This is because, according to the latest (2015) Global Burden of Disease estimates for “years of life lost to cancer per 100,000 people,” the global average (~2800) is lower than the U.S. figure (~3800). Most people around the world die of other causes before they survive long enough to die of cancer, but this is less true in wealthy countries like the United States.[↩]
59. On educational mobility, see e.g. OECD (2016).[↩]
60. For example, on economic well-being: suppose that Joe and Jane are medieval European laborers. They both invest in three years’ training to acquire additional economically valuable skills. Jane’s new skills include reading and writing, while Joe’s do not, but they both manage to double their annual wages as a result of their newly acquired skills. To me, it seems intuitive that the doubling of their income is a more important before-and-after difference in well-being than the difference in their literacy is.[↩]
61. On job satisfaction and other subjective measures, see e.g. Ng & Feldman (2014). On leisure time, see e.g. OECD (2009). On objective career advancement, see e.g. Ng et al. (2005).[↩]
62. Dunham (2008); BBC (2001); Philipkoski (2001).[↩]
63. Philipkoski (2001) says “[The Black Death] killed 200 million people in the 14th century and continues to kill about 3,000 people each year according to the World Health Organization,” but this citation of the WHO seems to apply only to the 3,000 figure, as I have been unable to find any reference on the WHO website to an estimate of 200 million deaths from the Black Death, either by searching the current WHO website or by browsing the Internet Archive’s copy of it from October 2001 (when Philipkoski’s article was released). In fact, the current WHO website estimates that the Black Death caused 50 million deaths.[↩]
64. E.g. using Google Scholar.[↩]
65. Du & Wang (2016), p. 203; Sun (2016); Titball & Williamson (2004); Derewenda et al. (2004); Dziarski et al. (2006); Bossi et al. (2004); Xu et al. (2011); Anish et al. (2013); Williamson & Oyston (2013); Titball & Leary (1998); Perry & Fetherston (1997); Erickson & Hinnebusch (2008); Rollins et al. (2003).[↩]
66. Titball & Leary (1998); Perry & Fetherston (1997); Erickson & Hinnebusch (2008); Rollins et al. (2003); Titball & Williamson (2004); Xu et al. (2011); Derewenda et al. (2004).[↩]
67. Page 690:
    

    Three pandemics, killing more than 200 million people… Only disease carrying mosquitos have caused as much misery as this fascinating order of insects aptly called Siphonaptera [i.e. fleas, the primary vector of Yersinia pestis]…

    Duplaix does not provide an estimated worldwide death toll for the Black Death of the 1330s-1350s. On p. 677 she writes “European cities [were] repeatedly hit by plague, 1347-1771; perhaps 50 million people die in all,” but she doesn’t provide a source for this figure either.[↩]

68. In the foreword to White’s book, Steven Pinker calls White’s book “the most comprehensive, disinterested, and statistically nuanced estimates available of the death tolls of history’s major catastrophes.” Pinker also relied on White’s work heavily in his Better Angels of Our Nature. See also Karnofsky (2015).[↩]
69. Wikipedia’s sources for this claim are a History Magazine article that I don’t have access to, and page 3 of Rosen (2007), which says:

    …the Plague of Justinian… killed at least twenty-five million people; depopulated entire cities; and depressed birth rates for generations precisely at the time that Justinian’s armies had returned the entire western Mediterranean to imperial control and only decades before Muhammad’s followers emerged out of Arabia to conquer Egypt, Palestine, Syria, Libya, Persia, Mesopotamia, and Spain.

    This passage, with its reference to (multiple) “generations,” and especially to “Muhammad’s followers,” seems to refer to several (perhaps all) waves of the plague, not just the first wave of 541-544.[↩]

70. In particular, I consulted most of the recommended English-language sources cited in Stathakopoulos (2000)‘s helpful review of the literature, and also Stathakopoulos (2004) and Little (2006).[↩]
71. Stathakopoulos (2004), pp. 138-140:

    Obviously the question of plague-induced mortality is of primary importance if modern scholars are to quantify the pandemic and its effects. However, this is extremely difficult because of the scarcity of reliable data on the death toll resulting from the infection…

    Using a mathematical model for epidemics and Prokopios’ data, Hollingsworth calculated the loss of life at Constantinople in 542: 244,000 deaths in a population of 508,000. This seems an authoritative figure derived from a mathematical model and as such it has been accepted as a reliable reflection of plague mortality… Nevertheless Hollingsworth based his calculations on some unreliable factors. First he declared that the plague that decimated Constantinople had been pneumonic rather than bubonic. This is, however, far from being an established fact. While pneumonic plague may have been present at Constantinople, as Prokopios’ mention of the vomiting of blood suggests, the vast majority of sources clearly record symptoms of bubonic plague. Furthermore he takes Prokopios’ statement of more than 10,000 victims a day at face value (he even concludes that there were about 10,500 because if [there had been] 11,000 the author might have said so) and thus arrived at such an elevated figure. Bratton [1981a, 1981b; both available online here] rightly dismissed these calculations. Instead he opted for the bubonic form of the disease with a duration of about 13 weeks (according to Prokopios’ account that the plague remained in the city for four months, in three of which it was at its peak). In a population (as estimated by Bratton) of 288,300, plague mortality would amount to 57,660 that is, 20 per cent of the entire population. If we use these calculations with the more plausible figure of about 400,000 as the pre-plague population of Constantinople we would arrive at… about 80,000 victims (or 20 per cent of the population and about 880 victims a day) — still a tremendously high number, but one that is not as exaggerated as Hollingsworth’s 244,000 (at 48 per cent). These calculations should not be taken at face value, but should rather be used as illustrating a general trend of plague-induced mortality.

    [↩]

72. Stathakopoulos (2008), p. 310:

    In an estimated realm covering some 1.4 million km² with a population density at 20 inhabitants per km² this would amount to roughly 28 million inhabitants (Koder 1984/2001: 154, between 24 and 26 million; Stein 1949-51: 154, 26 million).

    (The sources by Koder and Stein are not available in English and thus I could not consult them myself.) [↩]

73. Byrne (2004), pp. 7-8:

    Once in the Black Sea region the Plague acquired “biographers,” whose record is generally reliable on the course it took. The most famous and as yet unrefuted story has a colony of Italian merchants from Genoa coming under attack from Djanibeg, warrior lord of the Kipchak Khanate, a southern Russian nomadic state. By 1345 Djanibeg’s people had contracted the Plague and two years later catapulted it into the besieged Black Sea port city of Kaffa in the form of diseased corpses. Horrified Genoese took ship, taking the disease with them. Gabriele de’ Mussis, an Italian notary — or legal scribe — from Piacenza is our original source for this account, which seemed much more credible when scholars still believed that he was an eyewitness. But the Byzantine emperor and his historian in Constantinople also relate that it arrived from southern Russia. Ships from the Black Sea made port in Constantinople, setting off the horrors that the emperor and Gregoras record in their separate accounts…

    Once it hit the water, the epidemic could spread at the speed of a ship. From Constantinople sailors, rats, cargoes, or all three carried it out into the Mediterranean Sea. Messina, Sicily, and Alexandria, Egypt, were hit at about the same time, early fall 1347…

    …

    For some reason, Russia was spared until 1349 and beyond, indicating that the Plague did not move northward along the region’s river routes, but came eastward from Germany and eastern Europe. Polotsk, Pskov, Novgorod, Smolensk, and eventually Moscow — in 1353 — tasted the bitter pill.

    See also the map of the European spread of the Black Death on p. 32 of Kohn (2007).[↩]

74. In estimating death tolls, the following sources were most helpful (in chronological order):
    • McNeill (1976), ch. 4
    • Dols (1977), ch. 5.
    • Gottfried (1983), especially chs. 3-5
    • Platt (1991), ch. 1
    • Park (1993)
    • Ziegler (1997), i.e. the 2nd edition, especially ch. 14
    • Naphy & Spicer (2000), ch. 2
    • Scott & Duncan (2001), ch. 4
    • Byrne (2004), especially chs. 1 & 4
    • Benedictow (2004), especially ch. 33
    • Christakos et al. (2005)
    • Kelly (2006), i.e. the “reprint edition”, especially ch. 1
    • Kohn (2007), in particular the following entries: “Black Death (1347-1351)” and “Middle East Black Death Epidemics”
    • Noymer (2007)
    • Byrne (2012), in particular the following entries: “Black Death (1347-1352)”, “Black Death: Origins and Early Spread”, “Demographic and Economic Effects of Plague: The Islamic World”, “Demographic Effects of Plague: Europe 1347-1400”

    [↩]

75. On page 218, Dols writes:
    

    Thus, the degree of depopulation in Egypt resulting from the Black Death is far from certain. It can only be suggested at this stage of investigation that an Egyptian population of between 4.2 and 8 million may have declined by about one-quarter to one-third.

    And on page 220:

    If the population of Syria was 1,200,000, as claimed by Poliak, the medieval estimate of one-third would have reduced the population by 400,000.

    Of the rest of the Middle East, Dols merely says (pp. 222-223):

    For general population estimates of the Middle East, methods applied to the study of medieval European population and new techniques peculiar to the circumstances of Muslim society must be developed and employed. Of particular importance is the evidence produced by archeological excavations of Islamic sites for questions of urban density.

    What may be said with some assurance is that, on the basis of the fragmentary mortality figures for the disaster and comparison with [other] comparable plague epidemics… the Black Death substantially reduced the Middle Eastern population.

    [↩]

76. For example, Kohn (2007), p. 31, claims that the plague “killed an estimated 25 million Chinese, Indians, and other Asians during the 15 years before it entered Constantinople (Istanbul) in 1347,” but the author provides no source for this claim. McNeill (1977), ch. 4, is perhaps the most famous argument for the Black Death in China.[↩]
77. See e.g. Sussman (2011).[↩]
78. See page 156. Pinker’s data are from Wikipedia’s Abolition of Slavery Timeline. Pinker comments: “Included are all entries from “Modern Timeline” that mention formal abolition of slavery in a political jurisdiction.”[↩]
79. Existing efforts to estimate how many people are currently enslaved (UNODC 2016; Bales et al. 2016; ILO 2012) suffer from substantial methodological problems (e.g. see Gould 2010; de Vries & Dettmeijer-Vermeulen 2015), though efforts to improve availabile methods are underway (e.g. van Dijk & van der Heijden 2016). But even the highest estimate I’ve seen (Bales et al. 2016) suggests that 0.6% of people worldwide are “slaves,” under a much broader definition of “slave” than the one used throughout this report.[↩]
80. E.g. Walvin (2007):
    

    What the British and others discovered in the course of the nineteenth century, especially when they embarked on a new phase of imperial expansion, was that slavery was ubiquitous, as it had been before the launch of the slave empires in the Americas… The British not only abolished their slave trade (1807) and their slave systems (1838) but embarked on a remarkable crusade, which lasted throughout the nineteenth and into the twentieth century, to ensure that everyone else toed the British abolitionist line. Nations throughout Europe and the Americas, and later around the world, were pressurized to adopt the principle and practice of anti-slavery…

    They were not satisfied merely by overturning the slave systems imported into the Americas. Wherever the British encountered indigenous slave systems – in Africa, in India, in Arabia – there too they used the power of British diplomacy and military and naval muscle to secure abolitionist compliance…

    …at the very point when Americans shed their appetite for black slaves, there may have been more slaves in Africa than ever before, more even than had been shipped across the Atlantic in the entire history of Atlantic slavery…

    …there was a continuing demand for Africans in Arabia… Here was a region in which slavery had long predated the Atlantic slave system and continued long after its demise. Indeed it survived for more than a millennium, into the twentieth century, and may have engulfed more Africans than the numbers swallowed by the Atlantic slave ships.

    Drescher (2009), ch. 13.:

    When the Americas were closed to enslaved Africans in the 1850s and 1860s, the institution was attaining its maximum extension within Africa…

    …Deeply embedded in Africa, slavery demonstrated persistence and vigor into and past the fourth quarter of the nineteenth century. For many areas, historians have estimated the slaves at between one-fifth and one-half of the total population – from Madagascar to northwest Africa. On the eve of the era of intensified European imperialism, slavery was expanding in sub-Saharan Africa. Even at the height of the transatlantic slave trade, the majority of enslaved Africans were probably retained in Africa…

    …it would appear that Muslim civil society was not easily mobilized against slavery as a legitimate institution. Nor was the Islamic world unique in this regard. As of the late nineteenth century, the situation of Afro-Asian societies outside of Islam was much the same as that within its orbit of power. There was little evidence yet of any indigenous antislavery movement among those affiliated with Hinduism, Buddhism, or any of the sub-Saharan religions. It is the novel pressure of European intrusions and their reverberations, then, to which we must first look to account for the eastward sweep of abolitionist and liberationist movements in the half century between 1875 and 1925, when Western imperialism was reaching its apogee.

    [↩]

81. E.g. Walvin (2007), ch. 3:
    

    …slavery was commonplace throughout Arabia well before the rise of Islam. But as Islam spread, between the eighth and fifteenth centuries, and especially into black Africa, it extended and confirmed the commonplace use of slavery and slave trading. At the apogee of Islamic influence, slaves were imported into Islamic societies from Africa, Europe, Central Asia and even India.

    Drescher (2009), ch. 13:

    Exactly a century after the first great stirrings of abolition in Britain, slavery had been legally abolished [throughout the Americas by 1888]. In a broad swath of the Old World, however, stretching from the Atlantic coast of Africa through the eastern reaches of the Indian Ocean World, the institution of slavery remained both intact and robust. When the Americas were closed to enslaved Africans in the 1850s and 1860s, the institution was attaining its maximum extension within Africa.[↩]

82. E.g. Walvin (2007), epilogue:
    

    The British involvement with slavery underwent a remarkable transformation in the early nineteenth century… What the British and others discovered in the course of the nineteenth century, especially when they embarked on a new phase of imperial expansion, was that slavery was ubiquitous, as it had been before the launch of the slave empires in the Americas… The British not only abolished their slave trade (1807) and their slave systems (1838) but embarked on a remarkable crusade, which lasted throughout the nineteenth and into the twentieth century, to ensure that everyone else toed the British abolitionist line. Nations throughout Europe and the Americas, and later around the world, were pressurized to adopt the principle and practice of anti-slavery…

    They were not satisfied merely by overturning the slave systems imported into the Americas. Wherever the British encountered indigenous slave systems – in Africa, in India, in Arabia – there too they used the power of British diplomacy and military and naval muscle to secure abolitionist compliance. The British anti-slavery crusade was, in effect, global…

    Similarly, Martin Klein, in ch. 13 of Campbell (2005), writes that:

    …there were few free people in [the Indian Ocean] who had any objection to these institutions [of slavery]. Abolition was imposed by the British and later by other European powers, first on their own nationals, then on others.

    [↩]

83. I would very much like to have also consulted Dick Harrison’s three-volume world history of slavery (1, 2, 3), but unfortunately it is not available in English. I am also looking forward to the release of the 2nd volume of the Cambridge World History of Slavery, covering the period 500-1420 CE, but I have been told it will likely not be released until 2019.

    Additional relatively “general” sources on the history of slavery that I didn’t have time to consult include:

    • Patterson, “The Structural Origins of Slavery” (1977). Contains an attempt to estimate the proportion of people enslaved in some societies from the Murdock world sample.
    • Watson (ed.), Asian and African Systems of Slavery (1980)
    • Rodriguez (ed.), The Historical Encyclopedia of World Slavery (1997)
    • Blackburn, The Making of New World Slavery, 2nd edition (2010)
    • Eltis & Engerman (eds.), The Cambridge World History of Slavery, Volume 3: AD 1420–AD 1804 (2011)
    • Lovejoy, Transformations in Slavery, 3rd edition (2011)

    The most comprehensive bibliography of literature on slavery I know of is the University of Virginia’s Bibliography of Slavery and World Slaving. Unfortunately, the website version is now several years out of date, and does not make use of the regional and time period categories (listed here) that are available in the published editions of the bibliography and its many supplements; those categories are of course quite useful when seeking slave population estimates for particular regions and time periods. Supplements to this bibliography continue to be published in the last issue of each year’s volume of Slavery & Abolition.[↩]

84. Payne (2004), ch. 13:

    The demise of slavery was impelled both by economic factors and by feelings of empathy for slaves. The economic case against slavery is that it is inefficient. Being forced to work under duress, the slave tends to be a poor worker, with low productivity. At the same time, the maintenance of slaves is costly, for they must be housed, fed, guarded, and given direction for the accomplishment of every task. Therefore, if a slave is freed to work his own plot of land on a sharecropping basis, let us say, an increase in productivity will result. Working for himself, the sharecropper will be more diligent and thoughtful in carrying on production, and the owner spares all the cost of supporting, supervising, and guarding him. As a result, the owner of the land can make a greater profit than before.

    Over the years, this point about productivity played a powerful role in undermining the practice of slavery and led owners to give their slaves a greater degree of freedom. In medieval Europe, the transition generally took the form of converting slaves into serfs. Although the rights and duties of serfs were quite complicated and varied from place to place, the core of the serf’s obligation was to make a regular payment, a type of tax, to his lord. In most other respects, the serf was independent of the lord. He could work when he wanted, buy and sell property, come and go, even change residence. There were certain restrictions if he wished to marry a serf of another lord, and he was generally required to supply temporary labor or to serve temporary military duty. But, broadly speaking, the serf was beyond the brutal and restrictive treatment meted out to slaves.

    Serfdom as an alternative to slavery began to appear in Italy in the late years of the Roman Empire (a.d. 400– 500) as landowners grappled with the growing problem of slaves who could easily desert and who, given the weakness of Roman military forces, could not be easily recaptured. In France, serfdom had almost entirely replaced slavery by around 1200. In England, slavery rapidly disappeared after the Norman Conquest of 1066. Up until that time, slavery was common, with approximately 10 percent of the population being slaves. The Norman invaders, who considered France their home, freed slaves on the English estates they took over and made them serfs “to avoid the necessity of close supervision and management of slaves.” The economic pressures against slavery meant that this practice had largely died out in Europe by the late Middle Ages. It had also faded away in other places as well. In Japan, for example, it had become rare by the year 1200.

    It is important to note, however, that the decline in slavery in medieval times did not have a moral or legal foundation. Slavery was still legitimate and in varying degrees practiced. Europeans engaged wholeheartedly in the international slave trade, and there were some slaves in most countries. In Italy, for example, Florence and other cities of Tuscany had slavery and slave markets as late as the early 1800s. Thus, in Europe, slavery became merely a disused custom, not a condemned practice, which meant that Europeans easily revived it when it became convenient in the new colonies of the West Indies and North and South America. When these colonies were formed in the seventeenth century, they faced a great shortage of labor for their sugar, rice, and tobacco plantations. At the same time, a well-established slave trade coming out of Africa provided a supply to meet the demand. The result was that slavery became widespread in these areas.

    …Though some efforts were made in ancient and medieval times to alleviate the harsh treatment of slaves, there was little opposition to the institution of slavery itself. Even in the late Middle Ages, it was not questioned. A number of countries — England in 1569, Lithuania in 1588, Russia in 1679 — ended slavery on their own soil, but made no complaint of the practice as concerned other areas. The formal movement against slavery developed only in the late eighteenth century. Its founding moment was perhaps the English judicial decision of 1772 that any slave who might stand on English soil was freed, regardless of the nationality of the owner. In the following years, the Quakers and other activists in both England and Pennsylvania organized an abolitionist movement founded on the principle that “the slave trade was contrary to the laws of God and the rights of men.” Their agitation motivated the British government to abolish the slave trade in 1807 and led to the use of the Royal Navy to suppress that trade to both North and South America.

    The nineteenth century saw the abolition of slavery in the Western world. Most Latin American countries were ahead of the United States in abolishing slavery. Chile freed its slaves in 1823, Mexico in 1829, Peru in 1854. Brazil was the last in the region to abolish slavery, which it did in 1888. In other parts of the world, abolition came later still. China ended slavery in 1910. Korea legally abolished it in 1894, but the practice did not entirely end there until the 1930s.

    The Muslim world, reflecting its long tradition of violence and slave trading, was the last bastion of slavery in the world — or perhaps one should say is the last bastion, because a certain amount of clandestine trafficking of human beings still occurs in parts of North Africa and the Arabian peninsula. However, as the 1994 Encyclopedia Britannica observes, “Slavery no longer exists as a legal phenomenon recognized by a political authority or government any place in the world.”

    Walvin (2007), ch. 2:

    Slavery in western Europe was eventually eroded by the rise of feudalism, which involved the merging of slaves and free into a class of serfs… Even so, slavery managed to persist, especially in those European regions which were either physically close to Islam – Spain, for example – or which had important trading links to distant slave communities, notably Italy. But even where slavery in medieval Europe remained important and visible, it was never on the scale of slavery in the classical world or in Islam…

    …When the shift from slavery to serfdom took place, serfdom flourished in the growth of large estates, and in their need for a form of labour that was different from slavery. The rise of powerful local lords across western Europe was paralleled by their ability to force through important social changes, most notably in the use of labour. In England, this process was hastened by the Norman Conquest, and by the imposition of a foreign landlord class.

    What lay at the heart of this transformation – the ending of slavery – was to be found in other parts of Europe, though the exact timing differed from place to place. In Scandinavia, for example, slavery ended under pressure from many of the economic changes seen at work earlier in England. In Iceland, Norway and Denmark, slavery appears to have died out by the mid-thirteenth century; and in Sweden perhaps a century later. In Scandinavia, as elsewhere, the role of the early Christian church was sometimes ambiguous. The medieval Scandinavian church (as in England) held slaves on church lands, and most churchmen seem to have regarded slavery as a natural feature of the existing social order, though they cautioned that slaves should be treated as humans and as fellow Christians.

    …What happened in southern Europe was quite different again. It was understandable that slavery was more common across swathes of southern Europe. For a start, Islam had conquered much of Spain by 720, and was only stopped from sweeping through northern Europe by military defeat at Poitiers in 732. Islam remained in control of much of Spain until the late thirteenth century, and was only finally expelled with the fall of Grenada in 1492. The Islamic tradition of enslavement, and contacts with other Islamic societies in Africa and the eastern Mediterranean, meant that, in the very years when slavery was in sharp decline elsewhere in Europe, slavery was confirmed as an unquestioned feature of Iberian life. Muslims used Christian slaves, and Christian areas of northern Spain tended to use Muslim slaves. Muslim prisoners of war were employed as slaves for the building of the cathedral of Santiago de Compostela in the twelfth century; when the Aragonese took Minorca in 1287, they enslaved everyone except the rich, who were able to buy their freedom and flee to North Africa.

    Both Christians and Muslims in the Iberian peninsula raided each other’s communities for slaves. But the most plentiful source of slaves was Africa. By the 1240s Catalan merchants were buying slaves in North Africa, and Barcelona rivalled Majorca as a major slave market. Spain’s major Mediterranean ports teemed with ships loaded with goods (including slaves) from all corners of the Mediterranean. Slaves inevitably found their way throughout Iberian society into domestic work, urban employment and rural labouring. The ownership of slaves was widespread: artisans, monarchs and princes of the church all owned slaves. We know of slaves in 1431 in Catalonia who were owned by carpenters, laundrymen, blacksmiths, weavers, seamen, tailors, notaries, butchers and doctors. Slaves were rowers on the royal galleys in the late fourteenth century, while in the Balearic Islands slaves were essential as agricultural workers.

    In the two centuries to 1500 the Mediterranean slave trade thrived, with slaves (Muslim and ‘pagan’) arriving in Spain from around the Mediterranean and the Black Sea… It is impossible to be precise about the numbers of slaves in Spain; though they seem to have increased between 1300 and 1450, their numbers declined thereafter. Even so, it has been calculated that as late as 1428 one-tenth of the population of Majorca (where slaves were especially numerous) was enslaved.

    Walvin (2007), ch. 3, focuses on slavery in the Islamic world:

    …slavery was commonplace throughout Arabia well before the rise of Islam. But as Islam spread, between the eighth and fifteenth centuries, and especially into black Africa, it extended and confirmed the commonplace use of slavery and slave trading. At the apogee of Islamic influence, slaves were imported into Islamic societies from Africa, Europe, Central Asia and even India.

    …Slavery accompanied the spread of Islam across the Mediterranean, North Africa and into sub-Saharan Africa. In the process, overland and maritime trade routes evolved to supply slave markets with captives from the furthermost reaches of Islamic trade and influence. Black Africa proved to be a rich source of slaves for the major slave markets of the Mediterranean and the Near East. The slave routes across the Sahara, for example, survived from the seventh to the twentieth century, and millions of Africans were force-marched along them from their homelands to the slave markets to the north. One estimate puts the total number of slaves involved at more than seven million between 650 and 1900, though more recent calculations have revised that figure to between three and a half and four million. Even at that lower level, the trans-Saharan slave trade represents one of the largest examples of enslavement in world history…

    …Unlike the later Atlantic slave trade, Islamic slavery was primarily female – a clear enough sign that Islamic slaves were destined for different kinds of labour, mainly for domestic and sexual services. Female slaves toiled in a range of domestic work and other tasks across the Islamic world, from Córdoba to Baghdad. Men too were enslaved, large numbers being employed as eunuchs in harems and as literate slaves in administrative and educational roles. The Caliph of Baghdad in the late tenth century was thought to have had 7,000 black and 4,000 white eunuchs in his palace. From the earliest days, of course, slaves (many of them black) were employed in hard physical labour: in mines, in salt pans and for harsh agricultural work, as well as the military. By the eighth century, slavery was flourishing throughout the Islamic world, which stretched from the Middle East to Spain, though it is unlikely that slaves ever formed more than 5 per cent of the total population.

    Walvin (2007), chs. 4-7, describe the Atlantic slave trade:

    The broad slave-trading pattern of the following centuries was quickly established: a three-legged voyage, with ships sailing first from Europe to Africa, where Africans were collected, then across the Atlantic, and finally back to Europe with American produce. In time, this system became infinitely more complex, both commercially and geographically. Yet whatever the system, and even though transit times quickened, the experience for the Africans was an exercise in squalid misery. By even as early as 1600 perhaps 200,000 Africans had been shipped from West Africa.

    …The English involvement… was small beer compared to the existing Portuguese licensed trade. But the British, and the French and Dutch too, were not to be deflected… The Dutch were the first major power to begin the gradual erosion of Iberian power in the Atlantic, developing their own posts in Africa and for a time displacing the Portuguese in Brazil. In the period of their ‘Golden Age’, Dutch commercial expertise, finance, and merchant and naval power secured the Dutch commercial and political strength on both sides of the Atlantic. In the process they were able to disrupt Portuguese dominance of the Atlantic slave trade…

    By 1650 upwards of 800,000 Africans had been removed from West Africa by sea. By then, the trading and commercial structure of this maritime pattern of enslavement was well established, and its benefits had become unquestioned across Europe. As the British became the dominant force in the Atlantic slave trade, however, the numbers of African victims involved in the Atlantic slave trade were to reach dizzying heights.

    …

    The British had to learn what the Brazilians already knew: that if a tropical economy turned to sugar plantations, it needed lots of raw labour, and that labour could not be found among local Indians or immigrant Europeans. Africa, on the other hand, seemed ready to yield such labour on a vast and unending scale. Brazil had already absorbed growing numbers of Africans for its sugar plantations. Perhaps 50,000 had been transported to Brazil by 1600, another 100,000 over the next twenty-five years, and a similar number between 1625 and 1650. The British thus stepped in where others had gone before.

    …Africans were imported by the boatload, and by 1700 Barbados was home to more than 50,000 slaves. It was a pattern which was replicated through all the smaller British islands in the region: St Kitts, Nevis, Montserrat and Antigua. By the end of the seventeenth century these British islands (along with Jamaica) had absorbed more than a quarter of a million African slaves.

    …Less than fifty years after the British seizure of Jamaica, the enslaved population stood at 42,000; fifty years later it was 118,000. The numbers imported were even greater than these figures might suggest, for the death rate in the islands was high, while many other African arrivals were trans-shipped to other slave colonies.

    …This pattern was repeated on the Caribbean islands taken by the French… By 1700, some 124,000 Africans had been landed in the French islands. By then, the numbers of Africans forcefully removed to the Americas was massive: more than half a million to Brazil, some 450,000 to the non-Spanish Caribbean and almost as many again to Spanish settlements in the Americas…

    …North America’s conversion to African slavery came much later, and more slowly, than in the islands… The first Africans had been famously imported into Jamestown by the Dutch in 1619, but the economy of the Chesapeake region was driven forwards for the best part of three-quarters of a century not by slaves but by indentured labour, mainly from Britain. As tobacco gradually transformed the region, the plantations (generally much smaller than the sugar plantations in the islands) turned to Africans… As the Chesapeake disgorged ever more slave-grown tobacco (and by 1750 there were some 145,000 slaves there), it helped to dislodge Caribbean tobacco from the European market. By that date, 1750, another 40,000 slaves had been landed in South Carolina, destined mainly for the new coastal rice plantations. All these expanding economies were sustained by local slave populations which began to grow by natural increase, unlike the slave populations of most parts of the West Indies, which grew primarily through African importations. The end result was that by 1790 there were about 700,000 slaves in the newly formed United States.

    Even before then, by, say, the mid-eighteenth century, slavery had become a dominant feature of life in most corners of the colonial, tropical Americas. Though slaves were few in the more northern colonies, from Maryland south through Virginia, the Carolinas and Georgia, across the great arc of West Indian islands from Cuba to Trinidad, and south along the north-east coast of South America to Brazil, in addition to the Spanish empire in Central and South America, slaves were commonplace in a range of rural, urban and domestic employments. By 1790 Brazil was home to almost one million slaves, and slaves worked in all forms of economic activities.

    …By the time the British ended their own slave trade in 1807, they had shipped three and a quarter million Africans across the Atlantic…

    …

    Of the twelve million Africans loaded on to the ships, ten and a half million survived to landfall in the Americas. There were something like 27,000 known slave voyages, of which about 12,000 were British or British colonial, mainly North American. About 5,000 slave voyages originated in Liverpool. The majority of those African captives were male, although the gender ratio on the slave ships changed over time. By the last years of the slave trade, in the mid-nineteenth century, when the last, illegal slave ships heading for Brazil and Cuba were trying to outrun the British and American anti-slavery patrols, their human cargoes were largely very young and predominantly male Africans.

    …

    Between 1640 and 1700, 1.6 million Africans were landed in the Americas. In the course of the eighteenth century some six million Africans were shipped out of Africa. Despite the British and American abolition of the slave trade in 1807, a further three million Africans crossed the Atlantic as slaves in the nineteenth century, destined primarily for Brazil and Cuba.

    …

    Numerically, US slavery soon became the largest of all the slave economies. At American Independence in 1776 there were about half a million slaves in North America, and on the eve of the Civil War (1860) there were four million slaves in the US, of which 60 per cent worked in cotton. The US was home to the largest slave population in the Americas, even though it had imported the smallest proportion of Africans from the Atlantic slave ships.

    …

    Slave labour was an alien institution when Europeans made their first tentative explorations across the Atlantic. Within a century and a half it had become a vital means of settling and developing key regions of the Americas. Few doubted that whatever economic development had taken place in the slave colonies of the Americas could not have been achieved without slavery. In the process slave labour had itself been transformed from an outdated, almost forgotten institution into a vital force…

    In the epilogue, Walvin (2007) picks up the story again:

    The British involvement with slavery underwent a remarkable transformation in the early nineteenth century… What the British and others discovered in the course of the nineteenth century, especially when they embarked on a new phase of imperial expansion, was that slavery was ubiquitous, as it had been before the launch of the slave empires in the Americas… The British not only abolished their slave trade (1807) and their slave systems (1838) but embarked on a remarkable crusade, which lasted throughout the nineteenth and into the twentieth century, to ensure that everyone else toed the British abolitionist line. Nations throughout Europe and the Americas, and later around the world, were pressurized to adopt the principle and practice of anti-slavery…

    They were not satisfied merely by overturning the slave systems imported into the Americas. Wherever the British encountered indigenous slave systems – in Africa, in India, in Arabia – there too they used the power of British diplomacy and military and naval muscle to secure abolitionist compliance. The British anti-slavery crusade was, in effect, global…

    Anti-slavery seemed to be triumphant. In the course of the nineteenth century slave systems across the Americas either faded away or collapsed. There were only fifty years between the ending of British slavery and the demise of slavery in Brazil, the last slave outpost to fall in the America. By 1888, slavery had been swept away across the Americas.

    The same could not be said of Africa, however. Indeed, at the very point when Americans shed their appetite for black slaves, there may have been more slaves in Africa than ever before, more even than had been shipped across the Atlantic in the entire history of Atlantic slavery…

    …there was a continuing demand for Africans in Arabia… Here was a region in which slavery had long predated the Atlantic slave system and continued long after its demise. Indeed it survived for more than a millennium, into the twentieth century, and may have engulfed more Africans than the numbers swallowed by the Atlantic slave ships.

    By a bizarre twist of historical fate, slavery was even re-introduced into regions of the Western world which had not seen slaves for centuries. Recently historians have begun to consider the forms of slavery which lay at the heart of the dictatorial regimes of the mid-twentieth century. At first glance, what happened in Nazi Germany and its conquered lands, or in the vast stretches of Stalinist Russia and its satellite states, may seem far removed from the subject of this book. In fact, there were many close similarities. I was initially dubious when I first encountered the arguments that slavery was a basic and necessary component of both those tyrannical regimes, especially in the Second World War. It seemed to me that wartime Nazi Germany and Stalinist Russia occupied a qualitatively different position from, for example, the slave empires of the Americas. Today, I am not so sure, in large part because of the impressive and persuasive scholarship which has revealed the full details (and horror) of slave labour in both the Nazi and Stalinist empires. Wholesale upheaval and removal of people, relocation of massive communities and nations, millions of captives turned over to enslaved labour in brute conditions which often defy description – all this was common at the height of those tyrannies. Moreover, the numbers involved – measured in their millions in both cases – stand comparison with the numbers shipped across the Atlantic. It is thought, for example, that Nazi Germany used upwards of twelve million slave labourers during the Second World War, while the numbers shunted into Stalin’s labour camps in the Gulag remain uncountable but are certainly to be measured in millions.

    Drescher (2009) writes of the last 500 years of slavery (in the West) as a story of “dramatic expansions and contractions.” For example, on an unnumbered page before the title page, he writes:

    In the 1450s, when Europeans from the small corner of the globe least enmeshed in the institution first interacted with peoples of other continents, they created, in the Americas, the most dynamic, productive, and exploitative system of coerced labor in human history. Three centuries later, these same intercontinental actions produced a movement that successfully challenged the institution at the peak of its dynamism. Within another century, a new surge of European expansion constructed Old World empires under the banner of antislavery. However, twentieth-century Europe itself was inundated by a new system of slavery, larger and more deadly than its earlier system of New World slavery. This book examines these dramatic expansions and contractions of the institution of slavery and the impact of violence, economics, and civil society on the ebb and flow of slavery and antislavery during the last five centuries.

    On slavery and abolition in the “Old World,” Drescher (2009) writes (ch. 13):

    Exactly a century after the first great stirrings of abolition in Britain, slavery had been legally abolished [throughout the Americas by 1888]. In a broad swath of the Old World, however, stretching from the Atlantic coast of Africa through the eastern reaches of the Indian Ocean World, the institution of slavery remained both intact and robust. When the Americas were closed to enslaved Africans in the 1850s and 1860s, the institution was attaining its maximum extension within Africa. As noted in chapter 10, the World Antislavery Convention had been informed that there were 6 to 8 million slaves in India. Another contemporary writer placed the figure as high as 16 million or about one-tenth of the subcontinent’s population. At that moment, India probably contained more people in servile status than any other political unit in the world.

    …The transatlantic slave trade was characterized by relative stability in total volume during the first half of the nineteenth century, a sharp drop between 1850 and 1865, and final disappearance by 1870. In the Old World, Olivier Pétré-Grenouilleau estimates that the total long-distance Eastern trade… across the Sahara desert and Indian Ocean rose from 9,000 per year in the eighteenth century to 43,000 per year in the nineteenth century – a “veritable explosion” in coerced migration. In the Ottoman Empire, the slave trade appears to have reached its peak during the third quarter of the nineteenth century. Ehud Toledano estimates its volume, excluding Egypt’s internal traffic, at around 11,000 captives per year. In the 1860s, just as the Atlantic slave trade was closing down, Egypt received 25,000 slaves every year, five times its average during the previous decade. Into the last quarter of the century, the distribution of slaves may have altered between one or another sector but the continuity of the system showed no signs of dramatic decline…

    Deeply embedded in Africa, slavery demonstrated persistence and vigor into and past the fourth quarter of the nineteenth century. For many areas, historians have estimated the slaves at between one-fifth and one-half of the total population – from Madagascar to northwest Africa. On the eve of the era of intensified European imperialism, slavery was expanding in sub-Saharan Africa. Even at the height of the transatlantic slave trade, the majority of enslaved Africans were probably retained in Africa…

    …

    Many historians of late nineteenth-century Africa detail the peaking of slave raiding and trading in the late nineteenth century. They also note the presence of hundreds of thousands or millions of slaves in various African regions at the beginning of the “Scramble for Africa,” including upwards of a million in Buganda in the 1870s, nearly 3 million in French West Africa, and between 1 and 2.5 million in the Sokoto Caliphate, at the time of the colonial conquest. In the early 1900s, caravans could carry forced migrations of up to 50,000 a year through Angola… Estimates of enslaved Africans in the nineteenth century seem comparable in magnitude to those in the largest slave economies of the Americas in the 1850s. The proportion of slaves in most African societies where the institution flourished appears to have been as high or higher than it was in preemancipation Brazil, Cuba, or the United States…

    …About 150,000 bound servants left the African continent between 1850 and 1900. During the same period, almost ten times that number of African slaves were shipped to areas dominated by non-Europeans…

    …it would appear that Muslim civil society was not easily mobilized against slavery as a legitimate institution. Nor was the Islamic world unique in this regard. As of the late nineteenth century, the situation of Afro-Asian societies outside of Islam was much the same as that within its orbit of power. There was little evidence yet of any indigenous antislavery movement among those affiliated with Hinduism, Buddhism, or any of the sub-Saharan religions. It is the novel pressure of European intrusions and their reverberations, then, to which we must first look to account for the eastward sweep of abolitionist and liberationist movements in the half century between 1875 and 1925, when Western imperialism was reaching its apogee.

    Now, here’s Hunt (2015) on slavery in the ancient world:

    Slavery was a widespread institution in the ancient world (1200 BCE – 900 CE). Slaves could be found in simpler societies, but more important and better known was the existence of slavery in most advanced states. Indeed, it is hard to find any ancient civilizations in which some slavery did not exist…

    …we tend to know more about those states or empires that imported slaves than we learn about the less organized areas on their peripheries that typically suffered the enslavement of portions of their population. The larger and more centralized societies usually both did the enslaving and produced the written texts, art, or monuments that remain as evidence.

    …

    Historians often distinguish between slave societies and societies with slaves. In a slave society, slaves form a large proportion of the population, sometimes over 30 percent, and play a major role in the economy and especially the central sector of ancient economies, agriculture. Historians often claim that there were only five true slave societies in recorded history – including the ante-bellum South, Brazil, and the Caribbean – but more global perspectives have multiplied the candidates. Of the canonical five, there were two in our period: classical Athens, c. 500–300 BCE (and probably similar Greek citystates) and Roman Italy (and probably Sicily), c. 200 BCE – 200 CE. In contrast, societies with slaves include any society within which the institution of slavery exists. In the ancient world, this included almost all complex societies. Accordingly, groups such as the Essenes, a Jewish sect, who did not possess slaves, were noted as curious exceptions to the general acceptance of slavery.4 Indeed, most ancient states possessed more than a mere sprinkling of slaves. We find evidence of large concentrations of slaves in the cases of New Kingdom Egypt, Phoenicia (especially Carthage), Neo-Babylonia, Neo-Assyria, China, the Silla Kingdom in Korea, Visigothic Spain, and southern Iraq under the Abbasid dynasty. For example, in Qin and Han China, some elite individuals owned slaves in the thousands and slavery was associated with agriculture in the Han period. In one case, where we do possess decent statistics, we find that slaves made up over 10 percent of the population of some towns in Roman Egypt, not enough to make a slave society – especially since the slaves were domestic rather than agricultural – but hardly a marginal institution.

    …As a general tendency, the greater the reliance on slaves the more likely they were to be used in economically productive ways, especially in agriculture, and thus to play a large role in the economy. In contrast, virtually every society with any slaves had domestic slaves.

    …

    Although this volume focuses on 1200 BCE – 900 CE as a world with states, empires, and networks, significant portions of the human race were at this time still organized in pre-state societies ranging from bands of hunter-gatherers through village societies to tribal societies and chiefdoms. Our evidence, however, for pre-state slavery in the ancient world is for the most part either terrible or nonexistent. For example, slavery among Northwest tribes in North America may have been similar in ancient times to what it was when anthropologists first studied these peoples: slaves provided little economic benefit, but were rather given away or simply killed at potlatch ceremonies. Many languages in Africa have different words for “slave.” Historians have plausibly interpreted this diversity of nomenclature as evidence of the independent development of slavery in many places in Africa in the distant past. One working hypothesis, faute de mieux, would be that slavery among the peoples of the Northwest and Africa was similar a millennium earlier to how it appeared when our evidence begins. But the assumption that the distant past was unchanging just because it is unknown is optimistic at best. Somewhat more convincing are statistical surveys of large numbers of societies that show that slavery is rare among hunter-gatherers, is sometimes present in incipient agricultural societies, and then becomes common among societies with more advanced agriculture. Up to this point slavery seems to increase with increasing social and economic complexity. Fishing and especially pastoral societies are an exception to this developmental correlation in that they often have slavery. On balance, pre-state societies probably acquired and used slaves in different ways than did states: in particular, economic motives played less of a role in pre-state slavery. In many such societies slavery mainly involved the abduction of women as sexual partners.

    …

    A crucial property of slave systems… is the source of new slaves: whether the slaves are mostly foreigners reduced to slavery, are born into slavery, or are enslaved members of that society. Most historians believe that the last of these three sources, for people to be enslaved within their own society, is relatively rare. It is hard to sever ties with family, clans, and village without physically displacing a person. More important, perhaps, is that ruling classes have usually reduced their own lower classes to some sort of subjection: they have less motivation to destroy family and community ties and disrupt arrangements that already favor them.

    Campbell (2003) discusses the slave trade in the “Indian ocean world,” which is less well-described than the Atlantic slave trade:

    It is currently impossible to estimate with any precision the number of slaves traded in the IOW [Indian ocean world] given the duration of the slave-trade there, the limited nature of extant records, and the fact that, in contrast to the Atlantic system, IOW slaves rarely constituted a specialist cargo. However, slaves certainly comprised between 20 and 30 per cent of the population of many IOW societies, rising to 50 per cent and over in parts of Africa and in Indonesian ports. The slave-trade in the IOW involved overland and maritime routes. It started at least 4000 years ago, experienced a number of periods of growth, as in the last centuries BCE and first centuries CE, and during the eras of commercial expansion that accompanied the expansion of Islam in the late first millennium and the international economy in the nineteenth century.

    In the nineteenth century, as the IOW slave-trade peaked, it came under increasing international scrutiny, which induced slavers to adopt indirect routes and pass slaves off as non-slave porters, sailors, domestics, and even as children or other kin. Unlike the transatlantic slaving system, which was dominated by European finance, ships and personnel, indigenous agents, coastal Chinese, Bugis and ‘Malays’ in the eastern sector, and coastal Arabs and Indians, notably Gujeratis, in the western sector, largely funded and ran the multiple IOW maritime slave-trades. Moreover, it is possible that the greatest IOW slave traffic was overland, notably within Africa, Hindu India and the Confucian Far East.

    …

    It is in the IOW that the world’s first known legal documents referring to the sale of slaves have been discovered—the Ur-Nammu tablets (c.2300 BCE) of Mesopotamia, in present-day Iraq. A lively traffic in ‘people-as-property’ has persisted ever since in the IOW where an individual or group could ‘own’ slaves; corporate slave property appears to have been widespread in ancient India and remained common in Africa into the nineteenth century.

    Orlando Patterson’s foreword to Rodriguez (1999) provides the following overview of the world history of slavery:

    While universal, slavery varied considerably in its level of structural significance. In most areas of the world it was economically marginal, demographically no more than 5 percent of the population, and confined to the household…

    …With the possible exception of medieval Korea, it is only in the West that slavery became a major economic institution. It is remarkable that at all the watershed periods in Western history slavery played a key role in the transition process. Ancient Greece, the source culture of the West, rose to prominence on the basis of slave labor. By the late fifth century B.C., one in three adults in Athens was a slave, a proportion similar to the U.S. South at the height of its slave order. Rome was even more dependent on the institution, not only for its vast latifundia—the ancient counterpart of the modem plantation—but for its urban economy and for the lower-level clerical staff of its imperial bureaucracy. There was a resurgence of slavery in Europe during the late ninth and early tenth centuries; another during the late medieval and early Renaissance period of the Italian Mediterranean empires where the sugar plantation originated; and, of course, the rise of the modern state and capitalism went hand in hand with the rise of the slave plantation system and the vast intercontinental enslavement of some 12 million Africans in the New World.

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