Culture and Biology

I just finished reading Smail's On Deep History and the Brain. The first few chapters were a boring history of historians writing history... but the last few were pretty fascinating.

It's a common idea that humans stopped evolving the day that civilization started. Cultural change is so profound and occurs on a time scale so much faster than natural selection that it's easy to expect that we are essentially living post-biology. It usually takes millions of years for species to adapt to their environment: modern humans appeared about 50k years ago and we started experimenting with agriculture and cities only in the past 10k. The implication is that we are maladapted to our current lifestyle (which is pretty depressing!). The idea is that we're built to live in small bands on the savannas of Africa, not giant cities in all climates.

My favorite part of this book was where Smail makes the argument that the above idea is untrue - evolution is still affecting humans wherever we experience strong selection pressures - even in the span of a few thousand years. Well-established examples of modern humans evolving include the mutation that allows many of us to digest milk throughout our lives, and the sickle-cell gene which conveys resistance to malaria. I just read an idea the other day that ethanol tolerance may have been selected for to allow citizens to drink disease-free water in the form of beer and wine.

Even more intriguing were the ways that he demonstrated that culture can change biology. He gave many examples of ways in which our biological development is flexible, plastic and responsive to the way we live our lives. Smail describes the theory that much of human biology (especially behavior) develops as flexible "modules" that are affected by the physical and cultural environment. One example is that most primates live in rigid, complex social hierarchies. Most anthropologists believe that most human hunter-gatherers live in egalitarian societies that prevent hierarchies from developing. This "module" may have been suppressed by the culture of human hunter-gatherers and re-activated by modern civilization. Similarly, a friend of mine once explained to me how many modern humans often have overbites because eating soft cooked food fails to fully trigger lower jaw growth.

I also liked how he pointed out the just so story nature of much of evolutionary human biology thought. Just because you can come up with a reason why a certain phenomenon could be adaptive doesn't mean it really evolved for that function. Evolution is random and unpredictable - there are many ways that a given trait could show up. One example is the hypothesis that Hindus have a religious taboo against eating cattle because their farmers relied on them to plow their fields - and couldn't afford to be tempted to kill them during a lean year. Sure it could be true, but there's no way to prove it...

Pop psychologists like to suggest that men are only attracted to young women, and women are only attracted to older (wealthier) men - because this is what would be evolutionarily adaptive to both. Smail points out that the studies that support this idea relied on personal ads - not exactly a representative sample. Furthermore he points out that modern human hunter-gatherers (and likely all our ancestors) don't live this way in the first place. Typically, women gather most of the calories that the family consumes and when men are successful hunting they usually distribute it evenly among their tribe. When men have extra meat, they tend to give it to girlfriends instead of wives. Likewise, women rely on help with childcare more from mothers, sisters, brothers and boyfriends than they do their husbands.

It's intriguing to think about ways in which biology and culture could be intertwined. He discusses all sorts of possible ways - mainly revolving around brain-body chemistry. It's also much more encouraging to think that we're not stuck in a losing battle between biology and culture.