Such a thing
作者：Gregory Cochran @ 2016-4-19
“there’s no such thing as race” is a standard sentence in the United States and Europe. Conventional wisdom, and like so much conventional wisdom, false.
Of course there is.
First you need to define your terms. I would suggest that any population – a group whose members have mated within that group, almost entirely, for some time – and has experienced strong-enough natural selection to change significantly in some trait that we give a shit about can usefully be considered a race. Or a ‘goklu’, where goklu has exactly the same operational meaning as race, without having yet acquired any toxic associations.
Low levels of inward gene flow allow selection to change the frequencies of alleles, so mating within the group is important. Usually this endogamy is a natural consequence of geography (not much gene flow across the Atlantic before Columbus) but sometimes it has been caused by social rules, as in the case of the Ashkenazi Jews or the Hindu castes.
Low inward gene flow: in order for significant differences in the neutral genome to accumulate, there must have been < 1 immigrant per generation for tens of of thousands of years or more. That has happened sometimes, and not just with Neanderthals: sub-Saharan Africans and Eurasians were that separate until fairly recently, and have that kind of differences in their neutral genomes. For that matter, Bushmen and Bantu were genetically distinct for an even longer period. So it takes only a little gene flow to stop drift in its tracks.
Selection can be a lot stronger, and it takes more gene flow to scotch it. You could have effective selection for IQ among the Ashkenazi Jews even in the presence of as much as 0.5% inward gene flow per generation from the general European population. 2% would have been too much, though.
A long period of genetic isolation does not automatically generate differences in any particular trait: but it does show that there has been an extended opportunity for selection to operate effectively and generate population differences.
So when we see differences, how old are they? and how can we tell? Plausible selection pressures could generates one-std trait differences in as little as a thousand years, and in some cases, like the Ashkenazim, it likely has. In other cases it may have operated over tens of thousands of years, even as much as quarter of a million years (Bushmen/Pygmies versus other humans).
If the trait in question is characteristic of a geographically extended population, you might suspect that selection had operated over a long time. But since we now know that there have been many population expansions and replacements, you might be wrong. Ancient DNA may be a better guide.
So sometimes the explanation for the differences between two populations may go back deep into the Ice Age, but it might also have happened since the birth of agriculture, or even since the fall of Rome.
Suppose you have a one-std difference in some trait between two populations? What can we say about the genetic architecture? Well, sometime it boils down to the presence or absence of a single allele. Other times it is caused by a shift in the frequencies of a number of alleles that each have a small effect on the trait.
African-Americans average about 1-std lower in white count. That’s all due to the Duffy allele. All else equal, northern Europeans are a couple of centimeters taller than southern Europeans: that is caused by frequency differences in hundreds of alleles affecting height, a shift that on the whole has increased the frequency of plus variants.
So what to say to someone that asks about the ‘race gene’? First, you tell her that she’s an idiot. The complex of shovel-shaped incisors, thick hair, small breasts, more eccrine sweat glands, and a different shape to the hangy-down part of the ear, fixed in northeast Asia, is indeed caused by a single allele, an EDAR variant that is essentially nonexistent in Europe or Africa. On the other hand, Pygmy height, or the lack of it, is influenced by a number of alleles.
But the genetic architecture isn’t all that important: it’s the differences that matter. Pygmies are really short – that’s what matters.
Along those lines, Lewontin and other bullshit artists have tried to argue that genetic statistics are such that human groups can’t really be different. Most genetic variation in humans is within-group, rather than between-group: so fucking what? the same is true for dogs: am I supposed to think that pit bulls and Chihuahuas and border collies are ‘really the same’?
Having more plus variants in the alleles that affect a particular quantitative trait doesn’t show up in these genetic statistics (like Fst) at all. Neither would a big frequency difference in a single allele that had a big effect, like EDAR.
People are mostly about as different as they seem to be. There are exceptions, cases where an environmental insult makes a fair amount of difference. This is particularly the case with height, where nutritional status can easily create a 1-std difference. But height is influenced by genetics, too, and the shortest people (the Pygmies) are short for genetic reasons, not because they’re starving.
What about the magic immunity of the brain to natural selection? That’s nonsense, of course. We know, for sure, that different goklus have different distributions of personality traits – because they act significantly differently with 24 hours of birth. All the psychometric results indicate that goklus vary in intelligence too [perhaps 3 stds from highest to lowest] probably largely because of differences in the frequency of many alleles with small effects.