Schizotypy and fitness indicators

The Evolution of Autistic-Like and Schizotypal Traits: A Sexual Selection Hypothesis

Marco Del Giudice et al., 2010:

"The role of schizotypy in human mating has been further explored by Shaner et al. (2004, 2008a), whose evolutionary model treats psychotic-spectrum disorders (and more specifically schizophrenia) as the dysfunctional extreme of one or more sexually selected fitness indicators. Fitness indicators are traits with no immediate survival value, evolved through sexual selection to function as courtship ornaments due to their ability to reveal their bearer's genetic quality (lack of mutation load) and general conditions (Miller, 2000a,b). “Fit” individuals are able to display the attractive form of the trait, while individuals of low genetic quality and/or in poor conditions end up displaying its unattractive variant. In the model proposed by Shaner et al. (2004, 2008a), schizophrenia (whose typical symptoms are delusions, disorganized speech, reduced emotional expressiveness, poor sense of humor and impaired perspective taking) represents an aberrant form of human verbal courtship behavior, or, as the authors put it, a “catastrophic failure of mating intelligence.” Highly successful forms of verbal courtship require the opposite features: humor, skilled mind-reading, verbal creativity and emotional attunement, and so on. Several strands of evidence appear to support the hypothesis by Shaner and colleagues: for example, the typical age of onset of psychotic symptoms (adolescence and early adulthood) coincides with the peak of mating effort, and there are sex differences in age of onset that may reflect the different timing of maximal sexual competition in males and females. Moreover, dopamine agonists – known to stimulate courtship behavior in many species – also worsen the symptoms of schizophrenia, while dopamine antagonists have the opposite effect (see Kahn and Davis, 1995; Shaner et al., 2008a).

In this framework, schizotypy can be seen as a sensitivity-enhancing trait, so that high levels of schizotypal traits increase the correlation between genetic/environmental quality and mating displays. In other words, schizotypy would act as an “amplifier” of individual fitness as reflected in fitness-indicator traits, increasing both the risk of developing psychosis (when genetic quality is low and/or development is hampered by poor environmental conditions) and the likelihood of outstanding mating success (when genetic quality and environmental conditions are good)."

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Reduced Fertility in Patients' Families Is Consistent with the Sexual Selection Model of Schizophrenia and Schizotypy, Marco Del Giudice, 2010:

In the SSM, schizotypy enhances the sensitivity of a fitness indicator, by affecting brain processes so as to increase verbal/artistic creativity and other mating-related traits. As a result, schizotypal individuals enjoy higher mating and reproductive success when their genetic fitness is high, but suffer a higher risk of schizophrenia and reduced reproductive success when their genetic fitness is low. The figure shows two classes of genetic factors contributing to increased risk of schizophrenia: (a) fitness-reducing mutations and (b) schizotypy-increasing alleles