I think to answer this you need to break things down by region.
A look at our world in data shows that China was a 5th of the world population at the start of the first millennium, and it shrunk over the course of the millennium. Europe also shrunk, coinciding with the fall of Rome.
Africa, the Americas, and Australia gre at what looks like a fairly normal rate, but they are a much smaller percentage of the population.
So the explanation is likely to be local to the most populous regions, rather than some global event.
McEvedy and Jones actually discuss a regional breakdown in the final section of the book, but they speculate too much for the discussion to be useful, I think. They attribute any substantial slowdown in growth rates to population running up against technological limits, which seems like a just-so story that could explain anything.
They note that the 3rd century AD appears to have been a critical time, as it’s when population growth trends reversed in both Europe and China at around the same time: in Europe with the Crisis of the Third Century, and in China with the fall of the reconstituted Han dynasty and the beginning of the Three Kingdoms period. They attribute this to technological constraints, which seems like an unsupported assertion to me.
The other important population center is India, where we have very few records compared to Europe and China. Datasets generally report naively extrapolated smooth curves for the Indian population before the modern period, and that’s because there really isn’t much else to do due to the scarcity of useful information. This doesn’t mean that we actually expect population growth in India to have been smooth, just that in the absence of more information our best guess for each date should probably be a smoothly increasing function of the date. As McEvedy and Jones put it, “happy is the graph that has no history”.
I agree that locations isolated from Eurasia would most likely not show the same population trends, but Eurasia was ~ 75% of the world’s population in the first millennium and so events in Eurasia dominate what happens to the global population.
They attribute any substantial slowdown in growth rates to population running up against technological limits, which seems like a just-so story that could explain anything.
Well, that’s true, but at some level, what else could it possibly be? What other cause could be behind the long-run expansion in the first place, so many millennia after humans spanned every continent but Antarctica?
I’m very skeptical about explanations involving wars and plagues, except insofar as those impact technological development and infrastructure, because a handful of generations is plenty to get back to the Malthusian limit even if a majority of the population dies in some major event (especially regional events where you can then also get migration or invasion from less affected regions). I guess because they use nice round year numbers as cutoffs there could be artifacts of events right near the beginning or end of a millennium, but things happening in the 2nd or 3rd century AD aren’t candidates for that.
Well, that’s true, but at some level, what else could it possibly be? What other cause could be behind the long-run expansion in the first place, so many millennia after humans spanned every continent but Antarctica?
Technological progress being responsible for the long-run trend doesn’t mean you can attribute local reversals to humans hitting limits to technological progress. Just as a silly example, the emergence of a new strain of plague could have led to the depopulation of urban centers, which lowers R&D efficiency because you lose concentrations of people working together, and thus lowers the rate of technological progress. I’m not saying this is what actually happened, but it seems like a possible story to me.
I’m very skeptical about explanations involving wars and plagues, except insofar as those impact technological development and infrastructure, because a handful of generations is plenty to get back to the Malthusian limit even if a majority of the population dies in some major event (especially regional events where you can then also get migration or invasion from less affected regions).
I agree, but why would you assume wars and plagues can’t impact technological development and infrastructure?
Yes, it’s a possible story. And yes, wars and plagues impact tech development and infrastructure all the time. But I find it hard to think about how to draw a principled distinction between local growth slowdowns and hitting local limits to technological growth.
For example, in medieval Europe the Black Plague definitely depopulated the continent in ways that affected lots and lots of things, and there was no way they could reasonably have known how to do better. Resolving the plague wasn’t possible because the solutions were beyond the local limits of technological growth. If the same plague struck today, that wouldn’t happen, because we have the tools to deal with it. We understand sanitation, and disease vectors, and we can develop vaccines. It would be a blip of a decade and a few percent GDP growth, rather than half the population and centuries of recovery.
I think to answer this you need to break things down by region.
A look at our world in data shows that China was a 5th of the world population at the start of the first millennium, and it shrunk over the course of the millennium. Europe also shrunk, coinciding with the fall of Rome.
Africa, the Americas, and Australia gre at what looks like a fairly normal rate, but they are a much smaller percentage of the population.
So the explanation is likely to be local to the most populous regions, rather than some global event.
McEvedy and Jones actually discuss a regional breakdown in the final section of the book, but they speculate too much for the discussion to be useful, I think. They attribute any substantial slowdown in growth rates to population running up against technological limits, which seems like a just-so story that could explain anything.
They note that the 3rd century AD appears to have been a critical time, as it’s when population growth trends reversed in both Europe and China at around the same time: in Europe with the Crisis of the Third Century, and in China with the fall of the reconstituted Han dynasty and the beginning of the Three Kingdoms period. They attribute this to technological constraints, which seems like an unsupported assertion to me.
The other important population center is India, where we have very few records compared to Europe and China. Datasets generally report naively extrapolated smooth curves for the Indian population before the modern period, and that’s because there really isn’t much else to do due to the scarcity of useful information. This doesn’t mean that we actually expect population growth in India to have been smooth, just that in the absence of more information our best guess for each date should probably be a smoothly increasing function of the date. As McEvedy and Jones put it, “happy is the graph that has no history”.
I agree that locations isolated from Eurasia would most likely not show the same population trends, but Eurasia was ~ 75% of the world’s population in the first millennium and so events in Eurasia dominate what happens to the global population.
Well, that’s true, but at some level, what else could it possibly be? What other cause could be behind the long-run expansion in the first place, so many millennia after humans spanned every continent but Antarctica?
I’m very skeptical about explanations involving wars and plagues, except insofar as those impact technological development and infrastructure, because a handful of generations is plenty to get back to the Malthusian limit even if a majority of the population dies in some major event (especially regional events where you can then also get migration or invasion from less affected regions). I guess because they use nice round year numbers as cutoffs there could be artifacts of events right near the beginning or end of a millennium, but things happening in the 2nd or 3rd century AD aren’t candidates for that.
Technological progress being responsible for the long-run trend doesn’t mean you can attribute local reversals to humans hitting limits to technological progress. Just as a silly example, the emergence of a new strain of plague could have led to the depopulation of urban centers, which lowers R&D efficiency because you lose concentrations of people working together, and thus lowers the rate of technological progress. I’m not saying this is what actually happened, but it seems like a possible story to me.
I agree, but why would you assume wars and plagues can’t impact technological development and infrastructure?
Yes, it’s a possible story. And yes, wars and plagues impact tech development and infrastructure all the time. But I find it hard to think about how to draw a principled distinction between local growth slowdowns and hitting local limits to technological growth.
For example, in medieval Europe the Black Plague definitely depopulated the continent in ways that affected lots and lots of things, and there was no way they could reasonably have known how to do better. Resolving the plague wasn’t possible because the solutions were beyond the local limits of technological growth. If the same plague struck today, that wouldn’t happen, because we have the tools to deal with it. We understand sanitation, and disease vectors, and we can develop vaccines. It would be a blip of a decade and a few percent GDP growth, rather than half the population and centuries of recovery.