One issue to keep in mind is measuring wealth in calories and in other terms. People interested in malthusian theories focus on calories, while those interested in the advance of civilization may measure it in, for example, cloth. The malthusian theory predicts that the proportion of salary that goes to food should creep up in peacetime. But the advance of cities in the high medieval period made other products cheaper. When Braudel talks about economic recession, he's probably talking about abandonment of cities, which is not necessarily relevant to the malthusian question. So quality of life as measured by things other than food may have become high in 1300, but the famine of 1315-1317 suggests that the food situation was precarious. Why didn't they respond to the famine of 1315 by planting more land the following year? Was the land exhausted, the labor still in short supply (unlikely if they were starving in cities), or it takes too long to start new fields?
I don't think the failure of rebound from the Roman Empire, in itself, is so bad for the malthusian theory. But then the malthusian theory must predict that the shortfall is due to the lack of pax romana. It predicts that uninhabited areas are difficult to defend; or that farmers in such areas lose productivity by switching to crops that are hard to loot.
I think of Tuscany as an agricultural area. I guess this is evidence that I shouldn't. But I also think of Florence as important Renaissance city. Yet it was importing more food in 1300 than 1600? This is bizarre regardless of malthusian issues.
I don't have any direct knowledge of agricultural productivity in Eastern vs Western Europe, but I think the adoption of the high calorie-per-acre potato is correlated with low productivity and I think it was particularly popular in Eastern Europe. It is also a hard to loot crop. Corn and the potato are connected to population growth throughout Europe, suggesting that food limited growth before 1500. But some places (France?) didn't adopt them and didn't grow as fast, a rather non-malthusian situation.
Wikipedia says that during the entire Medieval period, "land was plentiful while labour to clear and work the land was scarce".
No, it just says it about 1000-1250. I think it means that raiders had been expelled from previously uninhabited land, allowing expansion. But at the end of this period, or at least by 1350, the situation was overextended. This is one case where I will grant a concern about speed of expansion. We know that in the right circumstances, such as colonial America, population can double each generation. You might expect the same from this description of this situation. This suggests that there is more to human psychology to switch on "high growth" than just food, which we certainly know from the demographic transition, but I'm reluctant to accept the description. The high initial cost of expansion may be relevant.
People interested in malthusian theories focus on calories
Which is of course total nonsense, as number of calories consumer per capita varies extremely little over huge differences in GDP. some data
So quality of life as measured by things other than food may have become high in 1300, but the famine of 1315-1317 suggests that the food situation was precarious.
Not at all. Even if there's plenty of unused land lying around, if you get unusually low yields, you can get famine. Few civilizations farmed spare land and threw away food, just in case the spa...
This is an attempt to list all of the possible ways in which humanity may avoid scenarios where the average standard of living is close to subsistence, in response to Robin Hanson's recent series of posts on Overcoming Bias, where he argues that such an outcome is likely in the long run.
I'll start with six, some suggested by myself, and others collected from comments on Overcoming Bias and Robin's own posts. If anyone provides additional ideas, I'll add them to the list.
(I have a more general point here, BTW, which is that predicting the far future is very difficult. Before thinking that some outcome is inevitable or highly likely, it's a good idea to repeatedly ask oneself "This is all the ways that I can think of why it may fail to come true. Am I sure that all of them have low probability and that I'm not missing anything?" There may be some scenario with a non-negligible probability that your brain simply overlooked when you first asked it.)
Singleton
A world government or superpower imposes a population control policy over the whole world.
Strong Security
Strong defensive technologies and doctrines (such as Mutually Assured Destruction) allow nations, communities, and maybe tribes and families to unilaterally limit their populations within their own borders, while holding off hordes of would-be invaders and immigrants.
Non-Human Capital
Maximizing the wealth and power of a nation requires an optimal mix of human and non-human capital. Nations that fail to adopt population controls find their relative wealth and power fade over time as their mixes deviate from the optimum (i.e., they find themselves spending too much resources on raising humans, and not enough on building machines), and either move to correct this or are taken over by stronger powers. (I believe that historically this was the reason China adopted its one-child policy.)
Unlimited Growth
We don't completely understand the laws of physics, nor the nature of value. There turns out to be some way for economic growth to continue without limit. (Robin himself once wrote "I know of no law limiting economic value per atom" but apparently changed his mind later.)
Selfish Memes
Memes that manage to divert people's resources away from biological reproduction and towards memetic reproduction will have an advantage over memes that don't. On the other hand, genes that manage to block such memes will have an advantage over genes that don't. Memes manage to keep the upper hand in this struggle (or periodically regain the upper hand).
Disease, Warfare, Natural Disasters, Aliens, Keeper of the Simulation
One or more of these come along regularly to keep the human population in check and per capita incomes above subsistence.