David Reich’s book has stirred up a lot of the usual suspects. Most are non-geneticists, but there are a few geneticists among them. Sorta kinda. Here’s an interesting example – something by Dan Graur, a geneticist currently at the University of Houston.
Graur says: “For selection to operate and counteract the effects of random genetic drift, the effective population size should be large. Unfortunately, the long-term effective population size for all the humans in the world is barely 10,000—lower than that of chimpanzee. By necessity, the effective population size of each “race” separately is much smaller. So, the chances that 74** loci will experience significant changes in allele frequencies simultaneously in each of the four populations is zero. With one locus, a change in human allele frequency may occur, albeit very rarely, as evidenced by the case of lactase persistence in North European and the case of the EDAR allele in East Asians. To imagine that 74 alleles change frequency in concert and that the 74 alleles have successfully battled genetic drift and recombination in merely 2,000 generations requires an extremely naïve and unsophisticated view of the evolutionary process.
Moreover, according to Augustine Kong, whom David Reich quotes, educational attainment is a deleterious trait that is selected against. The selection against educational attainment, according to Kung, is extremely powerful, so much so that differences in allele frequencies are observable after merely 3-5 generations (100 years). If one believes these claims, one should explain how come there are so many university graduates in Iceland. With such huge purifying selection against education, it’s a miracle that any one in Iceland knows how to read and write.
Kong A. et al. 2017. Selection against variants in the genome associated with educational attainment. PNAS 114: E727-E732
Moore DS, Shenk D. 2017. The heritability fallacy. WIREs Cogn Sci, 8:e1400. doi: 10.1002/wcs.1400
Okbay A et al. 2016. Genome-wide association study identifies 74 loci associated with educational attainment. Nature 533:539–542 ”
The interesting thing about this is that Graur has had prestigious jobs in areas relating to evolution, while apparently understanding nothing about it. Graur served as associate editor of the journal of Molecular Biology and Evolution from 1995 to 2011. Since 2009, he serves as associate editor of the journal Genome Biology and Evolution. From 2009 to 2011 he has held the position of Councillor for the Society for Molecular Biology and Evolution, won the Humboldt prize in 2011, and was elected a fellow of AAAS in 2015. In spite of this, every single statement in this short note is incorrect.
Graur says “For selection to operate and counteract the effects of random genetic drift, the effective population size should be large.” Well, it would be nice if the effective population size were large, but that is by no means necessary. German Shepherds were created in the 1890s, by interbreeding several breeds of dogs ( and wolves !), followed by selection for desired traits. That didn’t require tens or hundreds of thousands of dogs. Thoroughbreds are the fastest horses in existence: their effective population size is around 100. Dachshunds are smaller than they were in the 1970s – but then everybody knows they’re contrary enough to violate the laws of genetics. Born that way, probably.
I could go on – and on, and on. Every example we have of selection on domesticates is a counterexample to what Grauer is saying here. No farmer he. Does he think that some ancient geneticist corralled a million aurochsen in order to breed the domesticated cow?
A large population size is nice, because it generates more favorable mutations, but that is not necessary. Selection, at least in the short run, does not require any new mutations at all. Nice, because a large population size reduces the strength of chance, so the probability of the change in the trait under selection stalling or reversing in a given generation is lower – the results of selection become more predictable, especially in the short run. Next, Grauer talks about the long-term effective population size (EPS) in humans being around 10,000 – which he seems to think is too low for selection to work. He’s wrong, but that number is also the wrong number. He’s talking about the neutral-theory effective population size, which is a function [ harmonic mean] of long-term population size over the last million years or so – and it’s the wrong ‘effective population size’ for selection questions. There are different values of EPS for different questions. The right one is the “Variance EPS, which tells you the theoretical population size that yields the same noise in allele frequency change, right now. It basically measures how little a population is susceptible to drift.” The correct value of EPS, for different continental branches of humanity, has been hundreds of thousands to millions for a long time, well before agriculture was developed.
Graur is making a very basic mistake: he is perfectly happy making an argument to which there are many counterexamples. They don’t bother him. Even one counterexample should bother you. As I said, every domesticate is a counterexample to what he’s saying. We know of many genetically caused differences between human populations, such as height, skin color, disease resistance, ability to efficiently utilize certain foods, tolerate high altitude, low temperatures, high levels of arsenic, etc etc. By ‘we’ I mean anyone who can read. Some of those genetic differences are caused by new forms of one or a few genes ( like sickle-cell), others by small shifts in the frequency of many alleles that influence the trait.
Graur notes, incredulously, Augustine Kong’s work showing that the frequencies of variants influencing educational attainment are changing rapidly – in a way that decreases potential for educational attainment. We’re getting dumber. He asks how there could be so many university graduates in Iceland. But this kind of strong selection against potential for educational attainment – selection against intelligence – has been predicted for many years by people that understood that A. intelligence is highly heritable and B. On the whole smarter people, especially smarter women, have significantly fewer kids than average in contemporary society. This is almost certainly a new phenomenon, less than a hundred years old, just as mass higher education and artificial birth control are new things. Although Kong showed this directly, through genetic analysis, the idea is hardly new. R.A. Fisher talked about it, in The Genetical Theory of Natural Selection [published in 1930]. Of course Fisher understood polygenic selection pretty well too, having been the main developer of the theory of quantitative selection. Demographers in the 1950s talked about it. Cyril Kornbluth understood it ( ‘The Marching Morons’ ): but to be fair, Kornbluth was no ordinary man.