Cleverness made our species the most successful primate on Earth, thus claiming that human intelligence is adaptive sounds to be a triviality. Not surprisingly, when establishing long-lasting pair-bonds, humans exhibit mate preferences in favour of clever partners, apparently to increase the chance that their offspring will be as clever as possible. Contrary to this well-established view, here I argue that the adaptive nature of human intelligence has never been proven in a strict evolutionary sense. Furthermore, the exceptional rise of intelligence in our species (and the lack of comparable phenomena in other apes) is best explained within the context of the Hamilton-Zuk Hypothesis. Apparently, humans have been subjected to an exceptionally strong selection pressure exerted by pathogens and parasites, and the human brain is particularly vulnerable to infections, thus cleverness is an ideal character to signal heritable genetic resistance against infections. In this scenario, human preference for intelligent mates is to increase the offspring's resistance against pathogens. Among other phenomena, this hypothesis can explain why humans enjoy wasting most of their intellectual capabilities for totally useless purposes, why prehistoric humans developed brains that made them potentially far more intelligent than required by their physical environment, and why we experience a continuous increase of human intelligence even in modern societies. Briefly, I argue that (1) human sexual selection favours intelligence as a signal of genetic resistance against pathogens, and (2) that intelligence enabled the rise of our species (in terms of population size and distribution) as an accidental side-effect.
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