Planet Earth

Jerry Coyne on race: a reflection of evolution

Gene ExpressionBy Razib KhanFeb 29, 2012 1:53 PM


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After my post on the 'race question' I thought it would be useful to point to Jerry Coyne's 'Are there human races'?. The utility is that Coyne's book Speciation strongly shaped my own perceptions. I knew the empirical reality of clustering before I read that book, but the analogy with "species concept" debates was only striking after becoming more familiar with that literature. Coyne's post was triggered by a review of Race?: Debunking a Scientific Myth and Race and the Genetic Revolution: Science, Myth, and Culture. He terms the review tendentious, and I generally agree. In the early 20th century Western intellectuals of all political stripes understood what biology told us about human taxonomy. In short, human races were different, and the white European race was superior on the metrics which mattered (this was even true of Left-Socialist intellectuals such as H. G. Wells and Jack London). In the early 21st century Western intellectuals of all political stripes understand what biology teaches us about human taxonomy. Human races are basically the same, and for all practical purposes identical, and equal on measures which matter (again, to Western intellectuals). As Coyne alludes to in his post these are both ideologically driven positions. One of the main reasons that I shy away from modern liberalism is a strong commitment to interchangeability and identity across all individuals and populations as a matter of fact, rather than equality as a matter of legal commitment. In a minimal government scenario the details of human variation are not of particular relevance, but if you accept the feasibility of social engineering (a term I am not using in an insulting sense, but in a descriptive one) you have to start out with a model of human nature. So this is not just an abstract issue. For whatever reason many moderns, both liberals and economic conservatives, start out with one of near identity (e.g., H. economicus in economics). I want to highlight a few sections of Coyne's post:

What are races? In my own field of evolutionary biology, races of animals (also called “subspecies” or “ecotypes”) are morphologically distinguishable populations that live in allopatry (i.e. are geographically separated). There is no firm criterion on how much morphological difference it takes to delimit a race. Races of mice, for example, are described solely on the basis of difference in coat color, which could involve only one or two genes. Under that criterion, are there human races? Yes. As we all know, there are morphologically different groups of people who live in different areas, though those differences are blurring due to recent innovations in transportation that have led to more admixture between human groups. ... Why do these differences exist? The short answer is, of course, evolution.

The groups exist because human populations have an evolutionary history

, and, like different species themselves, that ancestry leads to clustering and branching, though humans have a lot of genetic interchange between the branches! But what evolutionary forces caused the differentiation? It’s undoubtedly a combination of natural selection (especially for the morphological traits) and genetic drift, which will both lead to the accumulation of genetic differences between isolated populations. What I want to emphasize is that even for the morphological differences between human “races,” we have virtually no understanding of how evolution produced them. It’s pretty likely that skin pigmentation resulted from natural selection operating differently in different places, but even there we’re not sure why (the classic story involved selection for protection against melanoma-inducing sunlight in lower latitudes, and selection for lighter pigmentation at higher latitudes to allow production of vitamin D in the skin; but this has been called into question by some workers). As for things like differences in hair texture, eye shape, and nose shape, we have no idea....

I have no idea if reading Coyne's earlier work influenced me, but observe that

he too emphasizes that human races are a reflection of evolutionary history.

Some of my interlocutors believe it is essential to have a tree-like phylogeny with no reticulation (gene flow across branches) to have a reasonable model for race, but I do not. That's because the focus for me is evolutionary history. I want to understand evolutionary history. Taxonomy is a means to that end. It is not the end. Coyne has a follow up post which will be of no surprise to reader of this weblog. But I do want to add a few things. 1) For pigmentation we do now understand its genomics relatively well. It seems that light skin emerged at least twice at the two ends of Eurasia, and, that it was a recent emergence (as evidence by markers of selective sweeps). 2) As for hair texture, there is some work which has shed light on this. East Asians in particular carry a variant of EDAR which gives them their distinctive thick straight hair. There has been less work on "woolly hair," but I suspect that it will be elucidated soon (there are some candidate genes, from linkage studies and animal models). Additionally, I think it is important to note that the dark-skin-as-protection-against-skin-cancer does not make much evolutionary sense. Melanoma strikes later in one's reproductive years. Rather, I accept that Nina Jablonski has the right of it when she argues that it protects against neural tube defects which arise because of various chemical changes which occur in one's biochemistry due to exposure to sun. Finally, I think Coyne underestimates the power of even gene genomics using haplotype based techniques in narrowing down on very specific geographical and population origins for segments of your DNA right now. The key is not where you come from, it is how segments of your DNA relate to the full range of segments of other peoples' DNA.

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