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One reason people deny HBD, is they don’t believe intelligence has evolved much or at all since modern humans left Africa tens of thousands of years ago, and diverged into the races we know today. Earlier today, commenter Swank defended this view:
…there are GOOD REASONS to believe intelligence hasn’t ‘evolved’ since then…
with pleiotropic and polygenic traits, the mutation rate is SLOW
in fact, the mutations humanity’s forebears that changed intelligence took several hundred thousand/millions of years to occur at a time. and it just seems like they were mutations quickly went to fixation, altering brain size/cranial capacity/whatever.
homo sapiens have not been around long.
so, with regard to skin color, eye color, nose shape, whatever…..
these things are likely controlled by not so many genes and subject to new mutations adding genetic variance….and we see diversity here.
other traits? not so much.
There have been scientists who’ve agreed with Swank about intelligence evolving slowly. For example, geneticist Spencer Wells says in his TED talk (see the 14 minute mark of video below), that from 1 million years ago, to about 65,000 years, there was a long period of cultural stasis where stone tools and other artifacts shows virtually no improvement. Then suddenly after 65,000 years ago, the archeological record shows radical improvement. Wells believes this was because fully complex language began to appear around that time.
Scholar Richard Klein has been making a similar argument for decades, but Klein believes this major genomic change occurred 40 or 50 thousand years ago.
Both Wells and Klein argued that the change occurred in Africa and caused humans to expand beyond Africa, but apparently disagree on when humans left Africa, which is understandable given the uncertainties in dating such ancient events (increasingly, scientists believe that behavioral modernity occurred much more gradually than Wells or Klein implied, but there does seem to be a consensus that technology was largely static from over 1 million kya to less than 300 kya)
Like Swank, Klein seems to think it was the last major cognitive change, stating:
What happened 40,000 or 50,000 years ago was the last major change in the genotype. At least the last major biological change. Evolution continues, but the evolution that’s involved in making us capable of wielding this vast variety of cultures–that probably stopped around 40,000 or 50,000 years ago and there’s been no essential change since.
Mitchell Leslie writes:
Forget about the construction of the first cities or the introduction of the internal combustion engine. The revolution that made the biggest difference occurred on the savanna of East Africa roughly 45,000 years ago, Klein and others maintain.
Stephen Jay Gould agreed with Klein, famously stating:
There has been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain
However scholar Greg Cochran is having none of it, stating:
I can’t think of any genuine reasons for thinking that human evolution had stopped. Some people seem to have thought that 40,000 years was small potatoes compared to the time since the chimp-human split (five or six million years), so that there wouldn’t have been much change over that time period. Of course this ignores the massive ecological changes that humans experienced over the last 40 millennia, and the resulting selective pressures. Others seem to have thought that newly clever humans instantly came up with a technological fix for any problem that arose, which would have removed the selective pressure associated with the problem. Face it, we’re not that smart. People suffered from malaria for thousands of years before figuring out that it was transmitted by mosquitoes (in 1897, by Ronald Ross) — and we haven’t knocked it out yet.
And often when we did solve problems, they didn’t stay solved. For example, whenever we came up with better methods of food production, population increased until people were hungry again. At that point you see selection for metabolic efficiency, for the ability to digest newly available foods such as milk, etc…
Speculating on why so many scientists believe there’s been little important recent evolution, Cochran states:
…Certainly some were (are) heavily invested in a vision of human sameness. I’m not sure how much of that is driven by practical payoffs: ethnic and racial differences continue to exist whether people “believe” in them or not…
…On the other hand, some certainly worry about political fallout of possible discoveries, about the impact on their NIH funding, etc….
… I think that some are genuinely confused. This is easier than you might think since very few biologists or human-science types know much about genetics and natural selection. Others simply don’t know much about human variation, while others are probably just spreading ink.
Elsewhere in the same interview Cochran states:
Cranial capacity has shrunk 10% in 15,000 years: that’s the fastest rate of change ever seen in the human fossil record, by far. Consider the number of genetic differences between humans and chimpanzees: they occurred over about six million years, from which you can determine the average rate or change. The number of genes that are apparently being replaced by new versions is much larger than you would expect from that long-term rate — something like 100 times larger.
Of course Cochran’s assuming the decline cranial capacity is genetic. Richard Lynn argued, that like the Holocene decline in height, it was caused by malnutrition/disease, and that its (full?) recovery in the 20th century partly caused the Flynn effect.