Gene-culture evolution and the Secret of our Success

I recently read a fascinating book on the story of human evolution called ‘‘The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter’’ written by Joseph Henrich, professor of evolutionary biology at Harvard University. Notwithstanding the tedious title, it altered how I fundamentally think about human beings as a biological species. In this post, I would like to record a couple of things that particularly caught my attention, and made me update my priors.

The first is the rebuttal of the idea that humans are extremely intelligent as individuals compared to other species: they are not. Henrich provides several examples – by recounting tales of lost European explorers from centuries past and describing more recent lab experiments on intelligence – to demonstrate how humans, when left to the elements and/or by themselves, struggle. Not only are comparable primates as intelligent at solving laboratory problems by themselves, many so-called ‘‘lower’’ species are more likely to survive by themselves in the wild than modern humans are – even in conditions where human hunter-gatherers have lived in societies for thousands of years.

Henrich theorizes that the reason behind why humans have succeeded is not individual intelligence, but, because of cultural knowledge built up over generations. This has given rise to a ‘‘collective brain’’ that gathered survival know-how through social learning between individuals – which then evolved a la ‘‘cultural evolution’’ over millenia. Lab experiments further lend credence to this theory: the same human babies that struggled against comparable primates at the same tasks individually, comfortably beat their ape cousins when working together in groups.

The second profound insight that I gathered from the book was the idea of ‘‘gene-culture co-evolution’’: that is, the idea that the causal relationship between genes and culture is not unidirectional, but goes both ways. A great example is the case of human beings with blue eyes. Originally, Henrich explains, all humans had brown eyes. However, when European settlers started growing wheat in the Baltic region, the increased bread in their diet (at the cost of fish and meat) led to a Vitamin D deficiency. This caused natural selection to prefer those humans who had a lighter skin colour, as the lower levels of melanin in the skin meant that humans in those regions could absorb more Vitamin D from the sun and compensate for its lack in their diet. The lightening of the skin required the OCA2 gene, that codes for the protein that produces melanin and gives the usual ‘‘dark colour’’ to the skin, to be restricted by a gene adjacent to it on the same chromosome. This in turn, also reduced the melanin in our eyes and hair – giving rise to, among other things, blue eyes (and possibly blonde hair?).

This remarkable genetic shift was driven by the advent of agriculture – which was a socio-cultural phenomenon – demonstrating how a change in lifestyle and culture, led to a biological, genetic change.

Henrich gives dozens of examples of how, more generally, cultural practices have shaped our biology today: from perspiration and the lack of fur on our skin being by-products of our group tracking and hunting activities, to our digestive system adapting to accommodate socially learned cooking practices over generations. The point that he repeatedly makes with all these examples, is that cultural evolution has gone hand-in-hand with biological evolution. Not only have we done what our biology has enabled us to do, but that our extreme capacity to learn socially and culturally has also adapted our biology to allow us to harness the full potential of our cultural knowledge. This, Henrich argues, is the secret of our success.

The Secret of Our Success by Joseph Henrich. Check it out on the publisher’s webpage.