Very skeptical about the testosterone thing.
http://www.ncbi.nlm.nih.gov/pubmed/3455741
"Mean testosterone levels in blacks were 19% higher than in whites, and free testosterone levels were 21% higher. Both these differences were statistically significant. Adjustment by analysis of covariance for time of sampling, age, weight, alcohol use, cigarette smoking, and use of prescription drugs somewhat reduced the differences. After these adjustments were made, blacks had a 15% higher testosterone level and a 13% higher free testosterone level. A 15% difference in circulating testosterone levels could readily explain a twofold difference in prostate cancer risk."
15% higher testosterone on average is no small matter. Keep in mind also that the study tested African-Americans (who have on average about 15% Caucasian DNA admixture.) This would seem to strongly indicate that actual Africans in Africa would have an even larger testosterone "advantage" as compared to whites.
The article points out that this readily explains a higher risk of prostate cancer. What political correctness prevents most people from pointing out is that it also probably goes a long way toward helping explain observed differences in crime rates and incarceration rates, especially when considered alongside
other studies which have shown the so called
warrior gene (which makes carriers display higher levels of aggression in response to provocation) exists in a much higher percentage of the African-American population than in whites. One study showed it in as high as 14% of blacks, the other showed it in 4.7% but both studies showed it in less than 1% of white men, putting even the 4.7% figure at nearly a 10 fold difference.
Whether people want to use the word "race" or not at some point they are going to have to come to grips with the fact that our species is not immune to natural selection pressures and that when different populations of our species are separated in dramatically different environments for tens of thousands of years that it
has an impact.
A tropical hominid species cannot migrate north into ice age Eurasia and undergo undeniable, well established changes in skin tone, hair consistency, bone shape, skull shape, etc and somehow magically have their brains and behavioral tendencies remain identical. We aren't special snowflakes of nature who have a "get out of natural selection free" card because otherwise our feelings might be hurt.
Our brains and hormone levels and behavioral tendencies
on average are just as up for grabs as those of any other species or sub-species. Ice age Eurasia was a very different environment to Africa where our species started out. Being the only group which
didn't interbreed with neanderthals and denisovans has to have had it's impacts too.
I find the changes in testosterone and the MAOA gene to be very unsurprising. I can easily see how an ice age, winter-bearing environment might select for greater impulse control, lower aggression, longer time horizon etc. Even in the course of one human lifetime we can see a small example, in the well known fact that crime rates go up in warmer months.
Back before we'd invented electric heaters and insulation and advanced structures, and keeping the fire going might mean the difference between life and death, I could easily see how the more impulsive, more violent, and less cooperative Eurasians might lose a great deal of their market share in those gene pools.
