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Do human races exist?
Do genes vary a lot more within human populations than between them? That seems to be the current wisdom. But wisdom sometimes needs challenging...
Written by Peter Frost.
Do genes vary a lot more within human populations than between them? That seems to be the current wisdom. Yet we see the same pattern elsewhere in the animal kingdom—not only with subspecies but also with related species that are nonetheless distinct from each other anatomically and behaviorally.
Back in the 1960s, American geneticist Richard Lewontin examined the genetic diversity of our species in terms of data from blood groups, serum proteins, and red blood cell enzymes. He found far more diversity within human populations than between them, be they large continental groups or small local ones:
The results are quite remarkable. The mean proportion of the total species diversity that is contained within populations is 85.4%, with a maximum of 99.7% for the Xm gene, and a minimum of 63.6% for Duffy. Less than 15% of all human genetic diversity is accounted for by differences between human groups!
It is clear that our perception of relatively large differences between human races and subgroups, as compared to the variation within these groups, is indeed a biased perception and that, based on randomly chosen genetic differences, human races and populations are remarkably similar to each other, with the largest part by far of human variation being accounted for by the differences between individuals. (Lewontin, 1972)
His finding was taken up by many others. For the founders of evolutionary psychology, John Tooby and Leda Cosmides, it rendered ‘‘implausible the notion that different humans have fundamentally different and competing cognitive programs’’:
Human groups do not differ substantially in the types of genes found, but instead only in the relative proportions of those alleles. […] What this means is that the average genetic difference between one Peruvian farmer and his neighbor, or one Bornean horticulturist and her best friend, or one Swiss villager and his neighbor, is 12 times greater than the difference between the ‘‘average genotype’’ of the Swiss population and the ‘‘average genotype’’ of the Peruvian population (i.e., the within-group variance is 12 times greater than the between-group variance) (Tooby and Cosmides, 1990, p. 35).
Lewontin’s finding has since been replicated not only with genetic markers and blood groups but also with mitochondrial and nuclear DNA. Apparently, looks can deceive. A Swiss person has no more in common with another Swiss than with a Peruvian … or anyone else in the world.
Genes versus taxonomy
Looks can deceive, but so can data. In other species, the genome can vary from one population to another in ways that scarcely resemble the way anatomy varies from one population to another. Yet anatomical development is supposedly programmed by the genome.
We see the same paradox when we look at genetic variation among dogs. Although dog breeds greatly differ in anatomy and behavior, they are barely discernable in the genetic data. There is much more diversity within them than between them:
[U]sing genetic and biochemical methods, researchers have shown domestic dogs to be virtually identical in many respects to other members of the genus. ... Greater mtDNA differences appeared within the single breeds of Doberman pinscher or poodle than between dogs and wolves. Eighteen breeds, which included dachshunds, dingoes and Great Danes, shared a common dog haplotype. Alaskan malamutes, Siberian huskies and Eskimo dogs also showed up in the common dog haplotype and were no closer to wolves than poodles and bulldogs. These data make wolves resemble another breed of dog. (Coppinger, 1995, pp. 32–33).
Even dogs as a whole are hard to discern in the genetic data:
To keep the results in perspective, it should be pointed out that there is less mtDNA difference between dogs, wolves and coyotes than there is between the various ethnic groups of human beings, which are recognized as belonging to a single species. (Coppinger, 1995, p. 33)
But aren’t dogs a special case? Dog breeds have been created through human selection for a few noticeable characteristics, like size, shape, color, and behavior. That focus on noticeability is presumably absent from natural selection.
Presumably. Yet wild animals often show the same pattern of genes varying much more within than between populations, even when the populations are related species and, sometimes, related genera (a taxonomic category that ranks above species and below family).
In the deer family, genetic variability is greater within some species than between some genera (Cronin, 1991).
Some masked shrew populations are genetically closer to prairie shrews than they are to other masked shrews (Stewart et al., 1993).
Only a minority of mallards cluster together on an mtDNA tree, the rest being scattered among black ducks. Although mallards, black ducks, and Mexican ducks are morphologically distinct, they are indistinguishable on the basis of mitochondrial or nuclear DNA (Avise et al., 1990; Lavretsky et al., 2014).
All six species of Darwin’s ground finches seem to form a genetically homogeneous genus with little concordance between mtDNA, nuclear DNA, and morphology (Freeland and Boag, 1999).
Beginning in the Pleistocene, a bird genus, the capuchino seedeaters (Sporophila), diverged into 11 species that are distinct in coloration and vocalization. Yet they are not distinguishable by mtDNA or nuclear DNA (Campagna et al., 2012).
In terms of genetic distance, redpoll finches from the same species are not significantly closer to each other than they are to related species (Seutin et al., 1995).
In Lake Victoria (East Africa), species of haplochromine can be easily told apart by their morphology and behavior but not by their nuclear or mitochondrial genes (Klein et al., 1998).
Neither mtDNA nor allozyme alleles can be used to distinguish the various species of Lycaedis butterflies, despite clear differences in morphology (Nice and Shapiro, 1999).
Many blood polymorphisms span not only different species but even different genera. In terms of the ABO system, for instance, a human individual may have more in common with some apes than with other humans. Such alleles, being of low selective value, can pass through one speciation event after another, thus making several related species look like one huge super-species (Brower et al., 1996; Funk and Omland, 2003; Klein et al., 1998; Knowles and Carstens, 2007).:
An extreme example is a tumor that spreads among dogs through sexual contact: canine transmissible venereal sarcoma. It began 11,000 years ago as a cancer in a dog. Today, it looks and acts like an infectious microbe, yet its genes would show it to be a canid (a mammal of the dog family), and some beagles may be genetically closer to it than they are to Great Danes (Strakova and Murchison, 2015; Yang, 1996).
A false assumption
Lewontin thought he was comparing apples with apples. He assumed that variation between populations is qualitatively the same as variation within populations.
It isn’t. A population boundary often coincides with an environmental one, i.e., a boundary between different natural habitats or, in the case of humans, different cultures. Because the problems of existence are not the same in different environments, natural selection will increase genetic differences across an environmental boundary. Such differences have real consequences for mind, body, or behavior.
Less consequential are genetic differences within a population. Because the problems of existence are similar, the uniform pressure of natural selection tends to level out any genetic differences that really matter.
The two kinds of genetic variation are thus not comparable. Variation between populations is more likely to affect mind, body, or behavior than variation within a population.
Since most genes have low adaptive value, often little more than junk DNA, the more consequential variation between populations is dwarfed by the less consequential variation within each population. That situation will gradually reverse if the populations are sufficiently isolated from each other. Over time, more and more inconsequential variation will build up between them, while the total variation within each population remains about the same.
But that takes time. Dogs have been diverging from wolves for longer than 15,000 years, yet the genetic differences between them are still less than those within many single dog breeds (Coppinger, 1995; Thalmann et al., 2013). Redpoll finches diverged into two species some fifty thousand years ago and have distinct phenotypes, yet their mitochondrial DNA still shows a single undifferentiated gene pool (Seutin et al., 1995).
The time depth is even greater with capuchino seedeaters (Sporophila). These finch-like birds began to split up into eleven distinct species around half a million years ago. Although they have diverged considerably from each other in their plumage coloration and their vocalizations, they show much less divergence over the genome as a whole. The various species still have a “blurry genetic identity … at least at neutral loci” (Campagna et al., 2012).
Humans are a young species, and their populations are even younger. The oldest one would be the Khoisans of southern Africa, who have been a distinct group for 150,000 to 260,000 years. Next come the Pygmies of central Africa, who split away from other humans some 170,000 to 100,000 years ago. Then comes the split between Africans and Eurasians some 50,000 to 60,000 years ago. Other splits go back to the last ice age, 10,000 to 25,000 years ago.
Many populations are even younger. The Parsis and the Ashkenazim, for instance, emerged as distinct groups a millennium or so ago (Frost, 2022a; Frost, 2022b).
Variation across the entire genome tells us little about variation in adaptive traits—the sort of traits that change as a population adapts to a new environment and new challenges. That is especially true for humans. Our species is young, and its populations even younger. They have acquired their specific characteristics by adapting to new environments over the past 50,000 years.
As a species gets older, its populations will diverge more and more from each other for non-adaptive reasons, as each gene pool accumulates its own dross and dreck. Between-population variation will be due more and more to restriction of gene flow, regardless of the gene’s adaptive value, and less and less to different adaptations to different environments.
So if we’re talking about real, functional differences in mind, body, and behavior, it’s not so much the passage of time that causes genetic divergence between populations. Rather, it’s the fact of their having to adapt to different environments with different challenges.
In real, functional terms, two young populations may differ a lot more than two old ones.
Peter Frost has a PhD in anthropology from Université Laval. His main research interest is the role of sexual selection in shaping highly visible human traits, notably skin color, hair color, and eye color. Other research interests include gene-culture coevolution. Find his Newsletter here.
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