Wednesday, July 26, 2017

The 10,000 Year Explosion, Conclusion: A Summary

The conclusion of Gregory Cochran and Henry Harpending’s The 10,000 Year Explosion: How Civilization Accelerated Human Evolution (2009) sums up the major hypotheses of the book as follows:
(1) genetic change and evolution have been preconditions for cultural change (one clear example being the expansion of hominid brains that led to speech and advanced tool making), even though cultural change is powerful and can be an independent force;

(2) genetic evolution and cultural evolution can also be inter-dependent, and influence one another in feedback loops;

(3) about 40,000 years ago human beings experienced a creative revolution during the Upper Paleolithic period in both Europe and northern Asia, which was driven by underlying biological and cognitive changes in Homo sapiens outside of Africa through new genes acquired by interbreeding with Neanderthals and possibly other archaic humans (e.g., the Denisovans);

(4) agriculture caused a 10,000 year explosion: it resulted in the acceleration of both cultural and biological evolution from much larger populations with a higher rate of mutation, in the new environments created by agriculture. Farmers evolved to be significantly different from hunter gatherers both in metabolism and cognition.

(5) evolution has continued until the present, because our environments have generally not been stable or static;

(6) biological and evolutionary change in human beings has also been a neglected but crucial driving force of human history, e.g., the epic expansion of the Indo-Europeans owing to their mutation allowing lactose tolerance into adulthood, the European settlement of the Americas, the failure of Europeans to penetrate Africa until the 1880s, and the evolution of the Ashkenazim in Europe (Cochran and Harpending 2009: 225–227).
Cochran and Harpending (2009: 207) conclude by speculating that perhaps even the industrial revolution and the rise of science have underlying biological or evolutionary influences not yet understood.

To sum up, we can also review how genetic/genotypic and hence phenotypic change can be driven in human societies, in accordance with standard principles of Darwinian evolution:
(1) direct adaptation, in which selection acts on individuals with (i) pre-existing individual genetic variation owing to sexual reproduction or (ii) with mutations;

(2) exaptation (some prior adaptation then “re-designed” to solve a different adaptive problem);

(3) as a by-product (or spandrel);

(4) sexual selection;

(5) genetic drift;

(6) genetic change caused by Malthusianism or differential survival rates, or elite reproductive advantage;

(7) genetic change induced by the policies and practices of governments and state-societies;

(8) genetic change induced by founder effects;

(9) unique genetic change induced by extraordinary events (e.g., plague, genocide, an ethnic minority subject to persecution), which might cause bottleneck effects, founder effects, etc.

(10) higher-level group evolutionary changes might be driven by inter-group competition and differences in group fitness (e.g., an analogy from the animal kingdom is evolutionary arms races).
Cochran, Gregory and Henry Harpending. 2009. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, New York.