mating intelligence [cont.]

two chapters by keller and shaner et. al. discuss the nature and importance of fitness indicators, the role of the brain as a mental fitness indicator and the implications of their theory in mental disorders such as schizophrenia.

consider a male peacock who invests considerable amount of energy in making a big shiny tail to display ostensibly during courtship. the cost of this investement alone can be seen as an indicator of this particular male's overall fitness, such as ability to produce a lot of color pigments, maintaining the size and shine of the tail and mental and physical agility to avoid predators at an increased risk of being spotted. on the other hand, a male peacock who cannot afford to invest in such a tail due to low fitness will have a much drabber tail. the tail of a peacock is thus a typical fitness indicator. the characteristics of such indicators are as follows:

1) high variance in measurable parameters, so that presumably it is easy for the chooser sex to pick from - the whole point is for the trait to be an indicator
2) variance correlates with underlying fitness
3) potential mate prefer th high fitness extreme
4) the trait is heritable
5) the trait is more conspicuous in the sex being chosen

this seemingly plausible argument runs into the "lek paradox", i.e. the contradiction between high sexual selection pressure and high variance. should all female peacocks prefer pretty tails, such genes will prevail and all male peacocks should have pretty tails, hence variance should be low. the resolution to this paradox comes from the speculation that fitness indicators, no matter how single-gene dependent to start with, inevitabily becomes polygenic because other traits have to coevolve to accommodate for the change in the indicator trait. e.g the peacock needs greater agility presumably to compensate for the more cumbersome tail. a polygenic trait inevitably becomes a bigger target for mutation accumulation due to the multiple genes involved, which leads to high variance. so the logic is that intensive sexual selection predicts a development of the trait into a polygenic one, which predicts the increase in its variance.

the above might be familiar to all of you who read evolutionary psychology and the likes. the developmet that the MI researchers want to bring home is that the human brain and its elaborate cognitive funcions such as language and creativity is an indicator for fitness. female preference for male brain power leads to the rapid selection of better brain genes. like other fitness indicators, intelligence, especially mating intelligence, is polygenic, prominently variable in males and heritable.

what's particularly interesting is that the authors suggest that mental disorders are serious failures of mating intelligence. schizophrenia is used as an example. in the analogy to peakcock tails, schizophrenia is like a drab tail, and it indicates mental unfitness, especially in mating. the onset of schizophrenia coincides with the start of reproductive period in humans, and it remits with the end of reproduction. it highly predicts mating failures and results social stigmatization. it is recently found to be polygenic, with many common develomental genes being the target for mutations discovered but not any schizophrenic switch genes. it is ostensible in male humas, the chosen sex and its development is sensitive to environmental factors that affect fitness.it is therefore merely the low end extreme of mating intelligence.

this led me to wonder about autism, which is clearly a spectrum of disorders with polygenic causes. however, it is not likely to be related to mating intelligence, because it is a childhood disease. as i wondered, i reached a section in shaner et. al. which actually discusses autism. they think that autism is an indicator of weakness in potential mating fitness not for mates to see, but for parents. very much like young birds who look better might get more parental investments, autism displays genetic unfitness that might prevent parents from investing limited resources in the affected child.