The human brain and its diverse capacities are so complex, and so costly to grow and maintain, that they must have arisen through direct selection for some important biological function. To date, it has proven very difficult to propose a biological function for human creative intelligence that fits the scientific evidence. We know that the human mind is a collection of astoundingly complex adaptations, but we do not know what biological functions many of them evolved to serve.
Evolutionary biology works by one cardinal rule: to understand an adaptation, one has to understand its evolved function. The analysis of adaptations is more than a collection ofjust-so stories, because according to evolutionary theory there are only two fundamental kinds of functions that explain adaptations. Adaptations can arise through natural selection for survival advantage, or sexual selection for reproductive advantage. Basically, that's it.
If you have two tools and one doesn't work, why not try the other? Science has spent over a century trying to explain the mind's evolution through natural selection for survival benefits. It has explained many human abilities, such as food preferences and fear of snakes, but it consistently fails to explain other abilities for decorative art, moral virtue, and witty conversation. It seems reasonable to ask whether sexual selection for reproductive benefits might account for these leftovers. This suggestion makes sexual selection sound like an explanation of last resort. It should not be viewed that way, because sexual selection has some special features as an evolutionary process. As we shall see, sexual selection is unusually fast, powerful, intelligent, and unpredictable. This makes it a good candidate for explaining any adaptation that is highly developed in one species but not in other closely related species that share a similar environment.
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