A few people have occasionally claimed that natural selection takes a long time to change any trait that might bother them – sometimes, they say this of polygenic traits, ones influenced by many genes, like height and intelligence. Kevin Mitchell has said this (“at least 100 millennia to evolve appreciably”), so has Brad Delong (an economist at Berkeley). David Reich mentions Joseph Graves, in a talk at Harvard, saying something similar in a lecture in 2016. They’re all 100% wrong: it is easy to select on polygenic quantitative traits, and we do it every day. Dogs vary a lot in height and most of the big differences are the result of fairly recent selection: nobody had Chihuahuas or Great Danes back in the Ice Age.
Human populations vary in height – not just from differences in nutrition. We know [work from the Reich lab] that northern Europeans are around a standard deviation taller than southern Europeans ( given adequate food), and we know some of the alleles behind that. Andaman islanders are four standard deviations shorter than the Dutch , Efe Pygmies almost five std shorter.
Probably the total range in humans, from the tallest (Dinaric Slavs, 6 1, to Efe Pgmies, 4 8) is six standard deviations. I’m sure that David Reich can explain to me how this is a small, even insignificant difference.
You may ask yourself why fairly prominent people manage to say instantly falsifiable things about human genetics. Good question. I might be partially protected from this error by preadaptation, having spent years and years walking past the Morrow Plots on my way to the main undergraduate library at the U of I. Delong has the excuse of not being any kind of biologist, but then again he ought to know that. A couple of us were trying to educate him on Twitter: he started accusing the mathematician involved of innumeracy, so the mathenaut called him “just another regression monkey”. Good times. As for Kevin Mitchell and Joseph Graves – well a lot of people in biology and medicine just don’t know much about selection. And of course in this context they don’t want to know.
Quantitative selection is a lot easier than people think. If I kidnapped a year’s worth of National Merit Scholars and dropped them on a deserted but fertile island, a new race with an average IQ around 130 would develop ( unless those little brainiacs escaped. You have to watch them all the time). If I dropped a lot of NBA and WNBA players, you’d see the tallest race, if we could just get them to reproduce.
But… there are some subtle points here. Great Danes exist and persist, but they have a bundle of health problems, and they don’t live too long (8-10 years). Wolves last around 15-16 years in captivity, with a record of 20. If you wanted to create a new race with an average adult height of 7 feet, I’m sure you could, but I’d bet money they’d have bad knees.
On the other hand, if they stayed 7 feet tall for a couple of million years, they would not be particularly prone to bad knees. There would be gradual selection for tougher knees: changes in development, changes in bones and tendons and cartilage, eventually perhaps fundamental changes in the architecture of the knee. There would be lots of little changes that made development among those giants more robust, changes that reduced the incidence of many problems that centers fall heir too.
Brain size in ancient and archaic humans was plenty big, but we don’t really see signs of rapid innovation, art, and decent fast food until fairly recently, 50,000 years or so. Some anthropologists says that humans were just as smart 100 or 150k years as they are today ( which may be true for some people) – but the notion that people managed to get smarter without showing any practical sign of it for 50 or 100k years is, in my opinion, just plain stupid.
So I think Kevin Mitchell ( not the other two) has a point. It’s possible, even likely, that the populations that have relatively high IQs today haven’t had them for very long, and that they’re not terrible well adapted to their new mental horsepower. Susceptible to various mental problems and illusions that would probably be a lot rarer if natural selection had had time to iron out the bugs.