The Economist explains:
At first sight this idea seems extraordinary, but closer examination suggests it is disturbingly plausible. Lots of features displayed by animals are there to show off to the opposite sex. Again, this involves a feedback loop. As the feature becomes more pronounced, the judge becomes more demanding until the cost to the displayer balances the average reproductive benefit.
Frequently, only one sex (usually the male) does the showing off. That makes the sexually selected feature obvious, because it is absent in the other sex. Dr Miller, though, argues that biologists have underplayed the extent to which females show off to males, particularly in species such as songbirds where the male plays a big part in raising the young, and so needs to be choosy about whom he sets up home with. Like male birds, male humans are heavily involved in childrearing, so if the mind is an organ for showing off, both sexes would be expected to possess it—and be attracted by it—in more or less equal measure.
Dr Miller suggests that many human mental attributes evolved this way—rather too many, according to some of his critics, who think that he has taken an interesting idea to implausible extremes. But sexual selection does provide a satisfying explanation for such otherwise perplexing activities as painting, carving, singing and dancing. On the surface, all of these things look like useless dissipations of energy. All, however, serve to demonstrate physical and mental prowess in ways that are easy to see and hard to fake—precisely the properties, in fact, that are characteristic of sexually selected features. Indeed, a little introspection may suggest to the reader that he or she has, from time to time, done some of these things to show off to a desirable sexual partner.
Crucially, language, too, may have been driven by sexual selection. No doubt Machiavelli played his part: rhetoric is a powerful political skill. But seduction relies on language as well, and encourages some of the most florid speech of all. Nor, in Dr Miller’s view of the world, is the ability to make useful things exempt from sexual selection. Well-made artefacts as much as artful decorations indicate good hand-eye co-ordination and imagination.
Miller doesn’t argue that all aspects of higher mental activity can be explained as an attempt to better attract a mate — his arguments assume a relatively complex mind already exists. The problem he seeks to explain is why we devote so much mental activity to things with no obvious connection to survival. Why do we dance, sing, write poetry, and paint? None of this helps us eat, drink, or find shelter. What else is there that is necessary to survival which might have helped encourage the development of such activity?
Well, finding and keeping a mate is an obvious option to explore. Even if some of these activities originally started for other reasons (painting or song might have started as an early means of more easily communicating information about where to find food), they expanded well beyond these uses and that would need explanation as well.
In fact, this might make Miller’s idea even more plausible — great prowess in non-useful painting or singing would indicate above-average ability when it comes to the vitally necessary painting and singing, which means that this person could be an above-average choice for a mate. This gives a whole new twist on the concept of “mental masturbation,” doesn’t it?