Motivated by the discussions about human brain size shrinking, I did some research on the matter.
The Brain size data are thoroughly summarized in this article [PMID 20378153] (http://www.ncbi.nlm.nih.gov/pubmed/20378153). The same point is made in a more popular fashion in this Times article (http://www.timesonline.co.uk/tol/news/science/article7060327.ece). The hypothesis of allometry is added by this blog entry (http://adhominin.com/index.php?id=4152453199173583192). The article (http://www.livescience.com/history/091113-origins-evolving.html) also neatly reviews the fact but unfortunately without providing any reliable references.
What is the fauceir perspective on that problem? Interestingly but not surprisingly, the shrinking of the human brain began with the evolution of human societies. You may date this back 5,000 or even 30,000 years. Humans organized in groups were much more effective at overcoming difficulties. An individual regardless its strength and intelligence had to succumb to a group. Therefore when humans began to form social groups an individual’s capabilities became less important for its own survival compared to traits that made this individual more suitable for this group. To put it bluntly, a quarrelsome individual even if strong and intelligent was less welcome in a group than a submissive one even if not so bright and tough.
The corresponding fauceir rule states: The adaptation of a slave fauceir is controlled by its master. Thus, with the formation of societies, humans as a biological being became slaves to the dominating master, the society they live in.
Often intelligent people were the most quarrelsome and therefore systematically eliminated. Yes natural selection began to work against intelligent individuals. A process like this, we observe in devolution and domestication. We have abundant evidence for this. It starts in prehistoric times. Remember the Bible, the Old Testament. Jacob’s intelligent son Joseph has been almost killed by his two less brainy brothers. He survived by accident and became a successful entrepreneur. In the New Testament, Jesus had not so much luck. In medieval times, his ostensible followers committed the first documented mass murder among such quarrelsome people during inquisition. Giordano Bruno was among them only because he lectured the heliocentric solar system. The culling of intelligent people proceeded til last century when Hitler, Stalin, and Pol Pot did the job.
In summary, Darwin’s thesis that women feel more sexually attracted to brainy males might be true at the level of human individuals, but it is overrun by social factors, and soon, as biology is controlled by society, women’s sexual preferences will adapt. If you wish, you can see the fulfillment of this prediction right now as more and more women select their partners for social status and not intelligence.