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Paolo Shirasi

Aug 11 • 33 tweets • 9 min read

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A VERY BASIC INTRODUCTION TO THE HEREDITARIAN POSITION ON RACE AND IQ.

PART 19: Rebutting the Environmentalist Claim That '50,000-150,000 Years Is Not Enough Time For Brain Differences To Evolve Between Groups'

Some scientists claim that there hasn't been enough time for meaningful evolutionary changes to take place in the human brain in the 50,000 to 150,000 years since humans left Africa — changes that might have caused differences in IQ between geographically-separated groups.

Here, as in so many other areas of dispute in the race and IQ debate, the genomics revolution once again comes to the rescue, showing that there has been more than enough time in this interval of human history for natural selection to cause genes-influenced brain differences.

David Reich: “You will sometimes hear that any biological differences among populations are likely to be small, because humans have diverged too recently from common ancestors for substantial differences to have arisen under pressure of natural selection. This is not true.”

The belief that there hasn’t been enough time for differences to evolve in human brains (and therefore affect our innate behavior) was plausible when biologists assumed that evolution was a slow process, but the decoding of the human genome has undermined that assumption.

Different human populations adapted to new environments and challenges as they spread out from Africa — obvious examples are genetic changes to allow for disease resistance, dairy consumption, and life in tropical, high-altitude, arctic, and other difficult climates.

“Selection pressures in response to regional conditions have influenced global human genomic diversity... None of these insights would be possible without global genome-wide population genetic data collected over the past 15 years.”

“Though we all share a human genome... genetic variation in that plan arises... as errors creep in each time DNA is copied... The accumulated genetic variation leads to variation in how our brains develop,” and ultimately to variation in cognition between groups (e.g., races).

Research using powerful new genomic tools is finding that over the past 1,000 to 15,000 years in Europe and parts of Asia "shifts in diet, lifestyle and environment introduced new [evolutionary] selection pressures..."

A 2019 study found direct evidence in the genome of evolutionary pressures taking place in European humans over the last 6,000 years by “comparing whole-genome data between Late Neolithic/Bronze Age individuals and modern Europeans,” including in “cognitive functions.”

Intelligence is a complex trait (i.e., “many genes each to small effect” influence it). A huge-sample (405,000 individuals) GWAS study of European, African, and East Asian populations in 2019 found that natural selection caused observed differences in the three complex traits...

... studied, and that this selection had occurred on the trait since "the divergence of these populations" around 50,000 to 150,000 years ago, making it appear unlikely that other complex traits (such as intelligence) would have escaped the same evolutionary processes.

Researchers now realize that natural selection “has been acting on us for the past 3,000 years, right up to the modern day... And it seems to be acting in surprising ways on complex traits encoded by multiple genes, such as those tied to intelligence..."

"There are mean differences in complex traits among global human populations... Our results support the hypothesis that natural selection has shaped the genetic differentiation of complex traits... among worldwide populations."

A 2021 GWAS for 870 complex traits (including intelligence) "found that 88% of these traits underwent polygenic change in the past 2,000–3,000 years."

The brain, of course, is a complex trait not immune from recent selection pressures. An interesting recent study found that a polygenic score for educational attainment has been decreasing over time in Iceland — evidence of very recent selection-driven brain changes.

A 2021 study found that natural selection recently altered a number of traits including brain size. (You'll recall that dozens of studies, including recent well-controlled ones involving thousands of individuals, have found a relationship between brain size and intelligence.)

New research is showing that polygenic selection over the past 2,000 years has influenced the physical structure of the brain, including the surface area of multiple cortical regions.

There's an explosion of research over the past few years shredding, study by study, the ideologically-driven talking point that meaningful changes in the human brain could not have occurred as population groups left Africa and spread across the globe.

Bottom line: Natural selection has operated on complex traits (which include intelligence) since humans left Africa 50,000 to 150,000 years ago, and some of this has occurred very recently, and probably has accelerated.

If in ONE human lifetime wild foxes were bred to become tame — a profound change in their brains — why is it so difficult to believe that human intelligence could have shifted 10% to 20% in one direction or another over THOUSANDS of human generations?

Analysis of the dog genome shows that it only took a few hundred years for *large* brain-based complex trait differences between dog breeds to take hold — differences that *greatly* exceed the relatively small change in just one human complex trait (intelligence).

“[S]elective breeding by humans has altered the gross organization of the brain in dogs... brain anatomy varies significantly in dogs, likely due to human-applied selection for behavior.”

Activist scientists usually won't have a problem with an evolutionary claim made about any part of the human body other than the brain. So it's not science at play; it's politics. There's are terms for this: “Evolution only below the head” and “cognitive creationism.”

“[Progressives] accept genetic explanations for things such as homosexuality,... addiction, and a variety of mental illnesses, but not for... group differences, and especially not when those... differences could explain... existing inequalities.”

If natural selection influenced the development of every system in the body (e.g., endocrine, immune, cardiovascular) why would our neurological systems (including the brain) have escaped this process? Why would the brain not been subject to adaptive demands?

Even when evidence of huge and obvious genetically-based racial differences in traits is on display for billions of people to see –- as it is during the Olympic Games — the social pressure to not acknowledge it overwhelms reality.

If 50,000 to 150,000 years was enough time for natural selection pressures to cause such huge differences in human performance such as those on display in the sprint and long-distance running events, why is it difficult to believe that the brain would not have been affected?

96 out of the fastest 100 sprinters of all time are of western near-coastal sub-Saharan African descent, an area that contains less than 5% of the world's population.

All 71 of the fastest marathoners of all time are of East African descent (2% of world population).

SOURCES:

science.sciencemag.org/content/354/63…

Epstein, D. (2014). The sports gene: inside the science of extraordinary athletic performance. London, UK: Penguin.

aeon.co/ideas/wired-th…

academic.oup.com/mbe/article-ab…