UPDATE: I’ve received an email from a researcher who points out that two of my statements are either misleading or incorrect in view of more recent work. Here’s the email and links:
In your interesting blog article “Are there human races?”, you write:”As has been known for a while, DNA and other genetic analyses have shown that most of the variation in the human species occurs within a given human ethnic group, and only a small fraction between different races. That means that on average, there is more genetic difference between individuals within a race than there is between races themselves.”– But this is patently false. I Tal (2012b) I show that pariwise genetic distances, from within- and between-populations, are substantially divergent (in fact, for Fst=0.15, reflecting average intercontinental differentiation from SNPs, the averages differ by almost 50%).
Also, you ask:”I’m not aware that anybody has tested the accuracy of diagnosing a single indvidual’s geographic origin from her multilocus genotype; if such studies exist, please let me know.”– Yes. In Tal (2012a) I develop models that show that classification accuracy approaches 100% even for very close populations, given enough loci. I then analyze recent empirical studies of human populations under this framework.
Tal O, 2012a. The Cumulative Effect of Genetic Markers on Classification Performance: Insights from Simple Models. Journal of Theoretical Biology. Volume 293, 21 January, Pages 206-218.
Tal O, 2012b. Two Complementary Perspectives on Inter-Individual Genetic Distance. In Press, BioSystems.
One of the touchiest subjects in human evolutionary biology—or human biology in general—is the question of whether there are human races. Back in the bad old days, it was taken for granted that the answer was not only “yes,” but that there was a ranking of races (invariably done by white biologists), with Caucasians on top, Asians a bit lower, and blacks invariably on the bottom. The sad history of biologically based racism has been documented in many places, including Steve Gould’s book The Mismeasure of Man (yes, I know it’s flawed).
But from that sordid scientific past has come a backlash: the subject of human races, or even the idea that they exist, has become taboo. And this despite the palpable morphological differences between human groups—differences that must be based on genetic differences and would, if seen in other species, lead to their classification as either races or subspecies (the terms are pretty interchangeable in biology). Racial delimitation could, critics say, lead to a resurgence of racism, racial profiling, or even eugenics.
So do races exist? The answer of Jan Sapp, a biology professor at York University in Toronto, is a firm “no”, as given in his new American Scientist piece “Race finished,” a review of two new books on human races (Race?: Debunking a Scientific Myth by Ian Tattersall and Rob DeSalle and Race and the Genetic Revolution: Science, Myth, and Culture, edited by Sheldon Krimsky and Kathleen Sloan). As Sapp notes, and supports his conclusion throughout the review:
Although biologists and cultural anthropologists long supposed that human races—genetically distinct populations within the same species—have a true existence in nature, many social scientists and geneticists maintain today that there simply is no valid biological basis for the concept. The consensus among Western researchers today is that human races are sociocultural constructs.
Well, if that’s the consensus, I am an outlier. I do think that human races exist in the sense that biologists apply the term to animals, though I don’t think the genetic differences between those races are profound, nor do I think there is a finite and easily delimitable number of human races. Let me give my view as responses to a series of questions. I discuss much of this in chapter 8 of WEIT.
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.
How many human races are there?
That’s pretty much unanswerable, because human variation is nested in groups, for their ancestry, which is based on evolutionary differences, is nested in groups. So, for example, one could delimit “Caucasians” as a race, but within that group there are genetically different and morphologically different subgroups, including Finns, southern Europeans, Bedouins, and the like. The number of human races delimited by biologists has ranged from three to over thirty.
How different are the races genetically?
Not very different. As has been known for a while, DNA and other genetic analyses have shown that most of the variation in the human species occurs within a given human ethnic group, and only a small fraction between different races. That means that on average, there is more genetic difference between individuals within a race than there is between races themselves. Nevertheless, there are some genes (including the genes for morphological differences such as body shape, facial features, skin pigmentation, hair texture, and the like) that have not yet been subject to DNA sequencing, and if one looked only at those genes, one would obviously find more genetic differences. But since the delimitation of races has historically depended not on the degree of underlying genetic differences but only on the existence of some genetic difference that causes morphological difference, the genetic similarity of races does not mean that they don’t exist.
Further, one wouldn’t expect human “races” or ethnic groups to show substantial genetic differences—there hasn’t been enough time for those differences to accumulate given that most human groups arose since our migration out of Africa between 60,000 and 100,000 years ago.
Nevertheless, even if most human variation occurs within rather than between races, there are statistical differences between human groups that can, when combined, be used to delimit them. Here’s a figure from the paper by Noah Rosenberg et al. (reference at the bottom) that uses these “multilocus” genotypes to distinguish human populations. Their study involved 1056 individuals studied from 52 geographic populations. The genetic analysis was comprehensive, involving 377 autosomal microsatellite loci (“autosomal loci” means “genes not on the two sex chromosomes”).
Rosenberg et al. fed the genetic data into a clustering algorithm that sorts individuals into a pre-specified number of groups, K (they used Ks between 2 and 6). I show below the data from predetermined clusters numbering 4,5, and 6. That algorithm sorts out populations into pretty distinctive genetic groups (remember, this involves combining data from many genes): either 5 or 6. At a sorting algorithm involving 5 groups, the authors note that the genetic clusters “corresponded largely to major geographic regions.” Those regions are roughly sub-Saharan Africa, Europe and the Middle East, Eastern Asia, Melanesia and Oceania, and the America. At K = 6, we get another group, the Kailash of northern Pakistan.
(Click to enlarge):
This shows the difficulty of answering the question of “how many races are there?” One could call Eurasians a race, or one could call Bedouins a race. It all depends on how finely you want to divide things up, and this is precisely what is expected if populations have evolutionary ancestry, which produces clusters of groups nested within each other. What is clear, though, is that human populations are genetically different, and can be diagnosed as genetically different using multiple pieces of DNA. Thus, although you may not be able to determine the geographic origin of a single person simply by looking at her morphology, you may be able to do that pretty accurately by combining information from lots of genes. I’m not aware that anybody has tested the accuracy of diagnosing a single indvidual’s geographic origin from her multilocus genotype; if such studies exist, please let me know.
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. Genetic drift is one explanation, but I suspect, given the profound differences between regions, that some form of selection is involved. In WEIT I float the idea that sexual selection may be responsible: mate preferences for certain appearances differed among regions, leading to all those physical differences that distinguish groups. But we have no evidence for this. The advantage of this hypothesis is that sexual selection operates quickly, and could have differentiated populations in only 50,000 years or so, and it also operates largely on external appearance, explaining why the genes for morphology show much more differentiation among populations than random samples of microsatellite genes, whose function we don’t know.
What are the implications of these differences?
Not much. There are some medical implications. As is well known to doctors, different populations have different frequencies of ailments. Some of that could, of course, be due to cultural rather than genetic differences, but some is undoubtedly genetic, and that should be taken into account when diagnosing an individual. Sickle-cell anemia, for example, is much more prevalent among sub-Saharan Africans and their descendants (e.g., American blacks brought over as slaves) than among Eurasians. Ashkenazi Jews, too, have their own unique spectrum of genetic diseases.
Everyone wants to know, of course, if different races differ genetically in their abilities, especially intelligence. While I think there may be statistical differences among races in these things, it’s not as obvious that sexual (or natural) selection would operate as strongly on genes involving these traits as on superficial external characteristics. We just don’t know, and in the complete absence of data it is invidious to speculate on these things. It’s just as scientifically unsupported to say, for example, that there is no difference among populations in mathematical ability as it is to say that there are differences. In the absence of data, we must follow the apophatic theologians and remain silent. And, at any rate, any such differences cannot be used to justify racism given the tremendous variation we see in other genes between members of different populations.
One can argue whether it’s even justifiable to scientifically study things like differences in IQ between populations given the political ramifications of finding differences. I go back and forth on this, but tend to think that it’s more interesting scientifically to study the differences that we know exist—in things like eye shape and skin pigmentation—and try to figure out why evolution promoted those differences.
I haven’t talked much about Sapp’s review, as I find it tendentious; nor have I read the books he’s reviewing. Perhaps I’ll change my mind about race after reading them, but based on what I know about human population differentiation, for now I think that “races” are biologically real (though we can’t delimit them precisely), and are certainly not “sociocultural constructs.” The “sociological constructs” thing is simply political correctness imposed on biological reality. In view of the morphological and genetic differences among human populations, how can such differences be “constructs”?
Rosenberg, N. A., J. K. Pritchard, J. L. Weber, H. M. Cann, K. K. Kidd, L. A. Zhivotovsky, and M. W. Feldman. 2002. Genetic structure of human populations. Science 298:2381-2385.