One reason people think the black-white IQ gap is at least partly genetic is its durability over time. The roughly one standard deviation IQ gap (15 points) between blacks and whites living for centuries in the United States was first observed in World War I during a time of extreme racism. It was thought that after decades of racial progress in civil rights, the IQ gap might diminish, but the most recent high quality IQ data shows the adult racial gap remains over 15 points (though the gap has narrowed to 12 points in children).
As Arthur Jensen noted, what makes the consistency of the U.S. black-white IQ gap especially striking is that it has endured over a period of such extreme environmental chance that the entire U.S. population is now performing as much as two standard deviations higher on IQ tests because of some combination of increased schooling and media making folks more test savvy, and increased health and nutrition causing brain size and function to improve. So even though Americans of all races today score some 30 points higher than their great grandparents in WWI, the U.S. gap between blacks and whites adults is still 15 points!
Of course one could argue that even a century of IQ gaps proves little, because even though the environment for black Americans has improved dramatically since WWI, they continue to lag way behind white Americans on most measures of socio-economic well-being.
What is needed is data going back much further in time and space. Obviously, we can’t get in a time machine and return to the paleolithic to give IQ tests to the ancestors of today’s blacks and whites, but what we can do is check the archeological record for evidence of prehistoric intelligence.
On page 134 of his landmark 2007 book Understanding Human History, Princeton astrophysicist Michael Hart documents some of the greatest achievements of the Upper Paleolithic.
Hart notes that with the exception of pottery, all of these inventions were made by people dwelling in Europe.
On page 135 he writes:
None were made by Negroids, nor by any other group living in tropical regions.
These facts are consistent with–and most easily explained by–the hypothesis that the groups that were living in cold climates had already evolved higher intelligence by 40 kya…
Critics dismiss IQ as just a score on a silly little test with no relevance to real world intelligence, however if racial differences in IQ predict real world creativity tens of thousands of years ago, this suggests the tests are measuring differences that are very real, very important, and very genetic and ancient in origin.
One problem with Hart’s book is that he credits the bow and arrow to Europeans. As commenter Jm8 likes to remind us, archaeologists working at South Africa’s Pinnacle Point cave site found evidence that humans had already invented the bow and arrow 71,000 years ago, likely before the major races had diverged. However preeminent paleoanthropologist Richard G Klein finds the evidence for this unconvincing (see the 28:06 mark in this video).
Another problem is Hart’s exclusion of the Ishango bone from his list of important paleolithic inventions, as some believe this 20,000 year old African object preserves the earliest known example of math, however skeptics believe the notches on the bone “may in fact be meaningless, simply scratched in to create a better gripping surface.”