Historians used to accept changes in people’s behavior as an explanation for economic events, like Max Weber’s thesis linking the rise of capitalism with Protestantism. But most have now swung to the economists’ view that all people are alike and will respond in the same way to the same incentives. Hence they seek to explain events like the Industrial Revolution in terms of changes in institutions, not people.
Dr. Clark’s view is that institutions and incentives have been much the same all along and explain very little, which is why there is so little agreement on the causes of the Industrial Revolution. In saying the answer lies in people’s behavior, he is asking his fellow economic historians to revert to a type of explanation they had mostly abandoned and in addition is evoking an idea that historians seldom consider as an explanatory variable, that of evolution.
Most historians have assumed that evolutionary change is too gradual to have affected human populations in the historical period. But geneticists, with information from the human genome
now at their disposal, have begun to detect ever more recent instances of human evolutionary change like the spread of lactose tolerance in cattle-raising people of northern Europe just 5,000 years ago. A study in the current American Journal of Human Genetics finds evidence of natural selection at work in the population of Puerto Rico since 1513. So historians are likely to be more enthusiastic about the medieval economic data and elaborate time series that Dr. Clark has reconstructed than about his suggestion that people adapted to the Malthusian constraints of an agrarian society.