I hope this isn't true, because if sexual selection is the cause of human intelligence, this means that American men are slowly turning into illiterate redneck bikers with excellent "game".
Foreign ladies FTW.
In the realm of intelligence, cultural progress (which encompasses better education, nutrition, technology, and everything else) has led to the Flynn effect, a gain of 3-5 IQ points per decade. Biological evolution in Homo sapiens has given us at most 100 IQ points (but probably closer to 50) in the last 74,000 years. The former is three orders of magnitude faster!
The Flynn effect itself will probably stop or slow all-but-completely anyway
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:
How did you come to believe that there could be such a thing as a genetic maximum to phenotypic traits?