Sir Ronald Fisher first emphasized that animals could choose their sexual partners for high fitness by favoring certain kinds of sexual display As we saw in Chapter 2, his 1915 paper introduced this idea of fitness indicators. But his 1930 book barely mentioned them, and devoted more space to the idea of runaway. When runaway sank into the quicksand of scientific skepticism, Fisher's even more obscure fitness-indicator idea sank with it. The idea waited thirty-six years for rescue. George Williams revived it in his influential classic, Adaptation and Natural Selection. Several decades on, his description of sexual choice for fitness remains unsurpassed.
It is to the female's advantage to be able to pick the most fit male available for fathering her brood. Unusually fit fathers tend to have unusually fit offspring. One of the functions of courtship would be the advertisement, by a male, of how fit he is. A male whose general health and nutrition enables him to indulge in full development of secondary sexual characters, especially courtship behavior, is likely to be reasonably fit genetically. Other important signs of fitness would be the ability to occupy a choice nesting site and a large territory, and the power to defeat or intimidate other males. In submitting only to a male with such signs of fitness a female would probably be aiding the survival of her own genes.
Since Williams's book became required reading for the new generation of biologists in the 1970s, the indicator idea started to catch on. It received another publicity boost when Richard Dawkins gave it a sympathetic exposition in his 1976 bestseller The Selfish Gene.
By the mid-1980s, biologists were seriously assessing the fitness indicator idea. The basic intuition seemed sound, but there were two technical problems so difficult that they took another ten years to resolve. One concerned the supposedly low heritability of fitness, and the other concerned the supposedly low reliability of fitness indicators. To understand how the human mind may have evolved as a set of fitness indicators, we have to understand these problems and their solution.
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