Psychologist Richard Lynn has long championed the controversial theory that cold winters selected for higher IQ because prehistoric humans had to be smarter to figure out how to survive in a cold climate than a warm one. Lynn uses this theory to explain why the highest national IQ’s and largest brain sizes are typically found in North East Asia, which was especially cold during the ice age. But one problem with this theory is that Arctic people, who are related to North East Asians and also evolved in cold climates and also have big brains, score over 13 points lower than North East Asians on IQ tests. In other words, Arctic people score like regular human populations; they did not get the unusual IQ boost the East Asians enjoy. To resolve this paradox, Lynn argues that North East Asians evolved in a very large population which increases the odds of favorable mutations occurring by chance. By contrast Arctic people evolved in a very small population, where there was less genetic variation for natural selection to operate on.
This would explain why both groups have above average brain size, but only East Asians have above average IQ. Natural selection (via cold winters) could only make arctic people smarter through selecting existing variation in brain size which has limits because brain size is only one determinant of intelligence, but with East Asians, there were other new sources of genetic brain variation, independent of brain size, for natural selection to also work with.
It’s interesting to note that East Asians were agriculturalists while Arctic people were hunter/gatherers. It’s also interesting to note that Lynn found a similar 13 point IQ gap in sub-Saharan Africa, where Africans who have historically practiced agriculture scored 13 points higher than hunter/gatherers like Bushmen. Is this gap genetic or environmental? And did agriculture raise IQ or does IQ cause agriculture?
This fits in well with a book called The 10,000 year explosion which argues that since the advent of agriculture, human evolution has been speeding up because the huge populations agriculture allowed gave rise to lots of new mutations for natural selection to work with. There’s only so far evolution can go with brain size because the brain is so metabolically expensive, and big brains are physically burdensome. Thus alleles that increase brain efficiency would have been especially useful, especially since the transition to agriculture robbed us of key nutrients, causing our brains to shrink. Agriculturalists likely compensated for this nutritional brain shrinkage by becoming genetically smarter independently of brain size. But in the last 150 years, we’ve been recovering all the brain size that agriculture robbed us of; giving us the best of both worlds: Hence the Flynn Effect.
So if agriculture, or more precisely, population explosions, raise IQ by 13 points, this would also explain the rise and fall of the Middle East. The middle east was the first region to develop agriculture, so their populations were probably the first to explode, giving rise to new genetic mutations which likely raised their IQ by 13 points. This huge IQ advantage explains why the middle east was the first region to develop a civilization. However as agriculture spread, so too did these new mutations, so pretty soon other populations got the same 13 IQ point boost, causing Middle Easterners to lose their competitive advantage. This explains why Middle Easterners were so far ahead of the rest of the world thousands of years ago, but are now no more advanced than most human cultures.