Box 5-1: Through a Glass, Darwinian

Runaway Sexual Selection in Humans: Did Woman Create Man?

At the end of Chapter 4 we suggested that human language abilities evolved very quickly as a result of runaway sexual selection where females came to select males on the basis of their language ability. Language allows one individual to assess certain cognitive abilities in the other. Through this mechanism, females who select mates with good language abilities, are also, in general, selecting mates with high levels of intelligence. In chapter 7 an argument is made with respect to creative/artistic abilities because they conferred the possessors of such abilities, novel methods for attracting a mate. Evolutionary psychologist, Geoffrey Miller, takes this argument of runaway-sexual selection in humans to a new level, saying that it is the basis of virtual all the unique qualities of the human mind.

Basically, Miller (2000) argues that the plodding pace of natural selection can not account for the rapid brain evolution and behavioral sophistication seen in our species. It is his contention that our huge brains and our amazing cognitive capabilities are the result of female mate choice. In other words, females preferred and probably still prefer to mate with males who are cerebrally endowed rather than cerebrally challenged. If this is true then male brains should have evolved to be bigger than those of females just as the tails of peacocks greatly exceed those of peahens. In fact, after adjusting for differences in body size, males have about 100 grams more grey matter than females, a difference of about 8 per cent. This difference does not appear to produce much of a difference in over all cognitive ability between the two sexes. Although men are generally better at women on spatial reasoning tasks, women are generally better than men on verbal tasks. The area where big differences are manifested is in the male penchant for creative display. In almost every activity, from science to performing arts to writing to architecture males do it more, and more competitively, than females. Moreover, this “creative display” reaches a peak between the ages of 20 and 30 years, a time of life when sexual competition and courtship activities are at their most intense.

There is a simple reason there is not a huge size disparity between the brains of men and women like the size disparity between peacock tails and peahen tails. It is because assessing cognitive traits requires cognitive ability. As we pointed out in chapter 4, language provides a window into another person’s behavioral tendencies and abilities. Unfortunately, language also provides a means of signaling false intentions and making false claims. Females would have had to develop better and better detection skills for spotting male deception. Unlike, selection for a simple physical trait like fancy tail-feathers or a large rack of antlers, selection for mental complexity necessitated an arms race between the sexes for greater and greater neural complexity. 

When we consider the complexity and sophistication of the human brain, it is hard to argue that it is the product of the selective forces of the environment. Even the pressures exerted by the social environment seem inadequate in accounting for human brain evolution. There are many species living in complex social environments but none approach humans in neural complexity. Miller’s female mate choice hypothesis provides a viable explanation for phenomena that are difficult to explain, otherwise. Without doubt, female mate choice has played a significant role in human evolution. On the other hand, women choose on the basis of a multitude of criteria and to say that women are simply selecting for better cognitive abilities is grossly simplistic and reductionistic. The full extent of the role of female mate-choice in humans has yet to be determined. Throughout our evolutionary history, female choice was one factor in a very complex and constantly changing system. The other form of sexual selection that Darwin described must have also played some part. Male-male competition in humans was not carried out with horns or antlers or slashing canine teeth but with cunning.