There is clearly a link between intelligence and puberty/speed of maturity. (I have been thinking about this because of a post on One STDV’s blog.)
In no other animal species do the young take so long to mature as do human children.
Between human races, blacks mature faster than whites who mature faster than Asians and that happens to match the ranking of the races’ average IQs.
Girls mature faster than boys and they enter puberty before boys. I believe that this explains why adult men score about four points higher on IQ tests than adult women. I also believe this at least partially explains why men are better at math than women and why Asians are better at math than whites. Late puberty seems to be especially beneficial for development of mathematical ability.
But what of the fact that children have been maturing faster? There has been much written about the “problem” of girls entering puberty earlier than ever. The same thing has probably been happening for boys, but it’s just harder to measure in boys because there’s no clear demarcation as there is for girls (age of first menses). Based on what I wrote in the previous paragraphs, this trend would suggest that people are getting less intelligent, but the Flynn effect has found just the opposite. A reasonable hypothesis is that the Flynn effect and earlier puberty are both caused by the same environmental factor, which is higher calorie diets which cause both the brain and the body to grow bigger and faster. The two effects partially cancel each other out, but the benefits of the brain growing bigger and faster earlier outweighs the detriment of early puberty.
Now, if the above is true, then we ought to be able to significantly increase people’s IQ if we can delay the onset of puberty without depriving them of calories and nutrition. Is this the reason why some ancient societies used to castrate young males? Were eunuchs better at their intended positions because they were smarter?