From my understanding, recent IQ gains are more akin to recent increases of the life expectancy.
Evolution slowly created a biological basis for the maximum life span/intelligence (including genetics-based variability with relatively few individuals able to achieve extremes).
Cultural progress just allowed more people to: a) live longer up to their genetic maximum, b) be smarter up to their genetic maximum. Thus it shifted the averages but not the extremes.
Flynn effect seems to support this: gains in IQ predominantly occur at the low end of the distribution.
See also discussion on iodine deficiency, it's the same principle:
Evolution slowly created a biological basis for the maximum life span/intelligence (including genetics-based variability with relatively few individuals able to achieve extremes).
Cultural progress just allowed more people to: a) live longer up to their genetic maximum, b) be smarter up to their genetic maximum. Thus it shifted the averages but not the extremes.
Flynn effect seems to support this: gains in IQ predominantly occur at the low end of the distribution.
See also discussion on iodine deficiency, it's the same principle:
http://news.ycombinator.com/item?id=386449