The Nurture of Nature

Fleet Street, watercolor by Ernest George (1839-1922). In England, middle-class families used to be so large that they overshot their niche and flooded the ranks of the lower class.

Until the last ten years it was widely believed that cultural evolution had taken over from genetic evolution in our species. When farming replaced hunting and gathering, something fundamentally changed in the relationship between us and our surroundings. We no longer had to change genetically to fit our environment. Instead, we could change our environment to make it fit us.

That view has been challenged by a research team led by anthropologist John Hawks. They found that genetic evolution actually speeded up 10,000 years ago, when hunting and gathering gave way to farming. In fact, it speeded up over a hundred-fold. Why? Humans were now adapting not only to slow-changing natural environments but also to faster-changing cultural environments, things like urban living, belief systems, and the State monopoly on violence. Far from slowing down, the pace of genetic change actually had to accelerate (Hawks et al. 2007).

These findings received a broader public hearing with the publication of The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. More recently, they have been discussed in a review article by historian John Brooke and anthropologist Clark Spencer Larsen:

Are we essentially the same physical and biological beings as Ice Age hunter-gatherers or the early farming peoples of the warming early Holocene? How has the human body changed in response to nine or ten millennia of dramatic dietary change, a few centuries of public health interventions, and a few decades of toxic environmental exposures? In short, how has history shaped biology? 

[...] But very clearly human evolution did not stop with the rise of modern humanity in the Middle to Late Paleolithic. Climatic forces, dietary shifts, disease exposures, and perhaps the wider stresses and challenges of hierarchical, literate state societies appear to have been exerting selective pressure on human genetics.

In short, we have become participants in our evolution: we create more and more of our surroundings, and these surroundings influence the way we evolve. Culture is not simply a tool we use to control and direct our environment. It is a part of our environment, the most important part, and as such it now controls and directs us.

Brooke and Larsen nonetheless feel attached to older ways of evolutionary thinking, particularly the "essentialism" of pre-Darwinian biology. We see this when they assert that “the essential modeling of the genetic code ended sometime in the Paleolithic." Actually, there was no point in time when our ancestors became essentially "human"—whatever that means. A Paleolithic human 100,000 years ago would have had less in common with you or me than with someone living 100,000 years earlier or even a million years earlier. Human evolution has been logarithmic—the changes over the past 10,000 years exceed those over the previous 100,000 years, which in turn exceed those over the previous million.

Clark’s model

Brooke and Larsen discuss Gregory Clark's work on English demography. Clark found that the English middle class expanded steadily from the twelfth century onward, its descendants not only growing in number but also replacing the lower classes through downward mobility. By the 1800s, its lineages accounted for most of the English population. Parallel to this demographic expansion, English society shifted toward "middle class" culture and behavior: thrift, pleasure deferment, increased future orientation, and unwillingness to use violence to settle personal disputes (Clark, 2007). 

Clark’s work is criticized by Brooke and Larsen on two grounds:

[... ] there is no biological evidence to support an argument for English industrial transformation via natural selection. More importantly, this was a process that—hypothetically—had been at work around the world since the launch of social stratification in the Late Neolithic and the subsequent rise of state societies.

How valid are these criticisms? Let me deal with each of them.

Is social stratification the only precondition of Clark’s model?

First, it is true that many societies around the world are socially stratified, but social stratification is only one of the preconditions of Clark’s model. There are two others:

1. Differences in natural increase between social classes, with higher natural increase being associated with higher social status.

2. Porous class boundaries. The demographic surplus of the middle and upper classes must be free to move down into and replace the lower classes.

These preconditions are not met in most socially stratified societies. Brooke and Larsen are simply wrong when they say: "The poor died with few or no children everywhere in the world, and across vast stretches of human history." In reality, there have been many societies where fewer children were born on average to upper-class families than to lower-class families. A notable example is that of the Roman Empire, particularly during its last few centuries: upper-class Romans widely practiced abortion and contraception (Hopkins 1965). A similar situation seems to have prevailed in the Ottoman Empire. By the end of the eighteenth century, Turks were declining demographically in relation to their subject peoples, perhaps because they tended to congregate in towns and were more vulnerable to the ravages of plague and other diseases (Jelavich and Jelavich, 1977, pp. 6-7)

Nor are class boundaries always porous. Social classes often become endogamous castes. This can happen when a social class specializes in "unclean" work, like butchery, preparation of corpses for burial, etc. This was the case with the Burakumin of Japan, the Paekchong of Korea, and the Cagots of France (Frost 2014). Because of their monopoly over a despised occupation, they were free from outside competition and thus had the resources to get married and have enough children to replace themselves. This was not the case with the English lower classes, who faced competition from “surplus” middle-class individuals between the twelfth and nineteenth centuries. Such downward mobility is impossible in caste societies, where “surplus” higher-caste individuals are expected to remain unmarried until they can find an appropriate social situation. 

A caste society thus tends to be evolutionarily stagnant. Lower castes in particular tend to preserve mental and behavioral predispositions that would otherwise be removed from the gene pool in a more fluid social environment.

Why did class boundaries remain porous in England? The reason was probably the greater individualism of English society, particularly its expanding middle class. Sons were helped by their parents, but beyond a certain point they were expected to shift for themselves. My mother’s lineage used to be merchants on Fleet Street in London. They were successful and had such large families that they overshot their niche. By the nineteenth century, some of them had fallen to the level of shipbuilding laborers, and it was as such that they came to Canada.

Is biological evidence lacking for Clark's model?

Brooke and Larsen are on firmer ground when they say that Clark's model is unsupported by biological evidence. There is certainly a lack of hard evidence, but the only possible hard evidence would be ancient DNA. If we could retrieve DNA from the English population between the 12th and 19th centuries, would we see a shift toward alleles that support different mental and behavioral traits? That work has yet to be done. 

Nonetheless, a research team led by Michael Woodley has examined ancient DNA from sites in Europe and parts of southwest and central Asia over a time frame extending from 4,560 and 1,210 years ago. During that time frame, alleles associated with high educational attainment gradually became more and more frequent. The authors concluded: "This process likely continued until the Late Modern Era, where it has been noted that among Western populations living between the 15th and early 19th centuries, those with higher social status […] typically produced the most surviving offspring. These in turn tended toward downward social mobility due to intense competition, replacing the reproductively unsuccessful low-status stratum […] eventually leading to the Industrial Revolution in Europe" (Woodley et al. 2017).

Again, work remains to be done, particularly on the genetic profile of the English population between the twelfth and nineteenth centuries, but the existing data do seem to validate Clark's model for European societies in general. Indeed, psychologist Heiner Rindermann presents evidence that mean cognitive ability steadily rose throughout Western Europe during late medieval and post-medieval times. Previously, most people failed to develop mentally beyond the stage of preoperational thinking. They could learn language and social norms but their ability to reason was hindered by various impediments like cognitive egocentrism, anthropomorphism, finalism, and animism (Rindermann 2018, p. 49). From the sixteenth century onward, more and more people reached the stage of operational thinking. They could better understand probability and cause and effect and could see things from the perspective of another person, whether real or hypothetical (Rindermann 2018, pp. 86-87).

As the “smart fraction” became more numerous, it may have reached a threshold where intellectuals were no longer isolated individuals but rather communities of people who could interact and exchange ideas. This was one of the hallmarks of the Enlightenment: intellectuals were sufficiently large in number to meet in clubs, “salons,” coffeehouses, and debating societies.

References

Brooke, J.L. and C.S. Larsen. (2014).The Nurture of Nature: Genetics, Epigenetics, and Environment in Human Biohistory. The American Historical Review 119(5): 1500-1513

https://doi.org/10.1093/ahr/119.5.1500 

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World. Princeton University Press: Princeton and Oxford.

Clark, G. (2009a). The indicted and the wealthy: surnames, reproductive success, genetic selection and social class in pre-industrial England.

http://www.econ.ucdavis.edu/faculty/gclark/Farewell%20to%20Alms/Clark%20-Surnames.pdf  

Clark, G. (2009b). The domestication of man: The social implications of Darwin. ArtefaCTos 2: 64-80. 

https://www.researchgate.net/publication/277275046_The_Domestication_of_Man_The_Social_Implications_of_Darwin 

Cochran, G. and H. Harpending. (2009). The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. New York: Basic Books. 

Frost, P. (2014). Burakumin, Paekchong, and Cagots. ResearchGate

https://www.researchgate.net/publication/260286339_Burakumin_Paekchong_and_Cagots

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA) 104: 20753-20758.

https://www.researchgate.net/profile/Henry_Harpending/publication/5761823_Recent_Acceleration_of_Human_Adaptive_Evolution/links/0c9605240c4bb57b55000000.pdf

Hopkins, K. (1965). Contraception in the Roman Empire. Comparative Studies in Society and History 8(1): 124-151.

https://doi.org/10.1017/S0010417500003935

Jelavich, C. and B. Jelavich. (1977). The Establishment of the Balkan National States, 1804-1920. Seattle: University of Washington Press.

Rindermann, H. (2018). Cognitive Capitalism. Human Capital and the Wellbeing of Nations. Cambridge University Press.

Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Research and Human Genetics 20(4): 271-280.

https://doi.org/10.1017/thg.2017.37