Complex Brains as an Advertisement for Genetic Fitness

The healthy brain theory suggests that our brains are different from those of other apes not because extrava- gantly large brains helped us to survive or to raise offspring, but because such brains are simply better advertisements of how good our genes are. The more complicated the brain, the easier it is to mess up. The human brain's great complexity makes it vulnerable to impairment through mutations, and its great size makes it physiologically costly. By producing behaviors such as language and art that only a costly, complex brain could produce, we may be advertising our fitness to potential mates. If sexual selection favored the minds that seemed fit for mating, our creative intelligence could have evolved not because it gives us any survival advantage, but because it makes us especially vulnerable to revealing our mutations in our behavior.

Extreme vulnerability to mutation sounds like something that natural selection could not possibly favor. Precisely. It is what sexual selection through mate choice favors. Once sexual choice seized upon the brain as a possible fitness indicator, the brain was helpless to resist. Any individuals who did not reveal their fitness through their courtship behavior were not chosen as sexual partners. Their small, efficient, ironclad, risk-averse, mutation- proof brains died out with them. In their place evolved our sort of brain: huge, costly, vulnerable, revealing.

Our species was not the first to stumble upon the fact that complex behaviors make good fitness indicators. Songbirds reveal their fitness by repeating complicated, melodious songs. Fruitflies do little dances in front of one another to reveal their genetic quality Bowerbirds construct large mating huts ornamented with flowers, fruits, shells, and butterfly wings, presumably to reveal their quality. In fact, many species appear to use their courtship behaviors as fitness indicators. The distinctive thing about humans is that our courtship behavior reveals so much more of our minds. Art reveals our visual aesthetics. Conversation reveals our personality and intelligence. By opening up our brains as advertisements for our fitness, we discovered whole new classes of fitness indicators, like generosity and creativity.

The cognitive tricks performed by our complex brains may not have a survival benefit, but they do advertise the overall fitness of our genes.