How might this be used to inform evolutionary questions? Standard twin analyses have shown in a Swedish population that variation in fitness (both first and second generation reproductive PLX-4720 purchase success) is substantially heritable [19], but it is impossible with this type of analysis to determine to what extent the genes that affect fitness in Sweden are the same or different from those that affect fitness in small-scale, natural fertility, traditional

societies that are more similar to our ancestral circumstances. However, this could in principle be tested with large genotyped samples from Western and traditional societies, which would shed light on the genetic differences between modern and ancestral fitness. Another function of genetically informative designs is to provide crucial controls

Vorinostat cost for genetic and familial confounds in tests of evolutionary hypotheses. For example, it has been hypothesized that father absence causes early physical and behavioral sexual maturation (age-of-menarche, age at first intercourse) because of an evolved mechanism that strategically calibrates development to the riskiness of the environment [20]. However, Mendle et al. 21 and 22] showed that these effects were not present when familial (including genetic) confounds were controlled for using the children-of-twins design: cousins discordant for father absence showed no differences in sexual maturation. This finding is inconsistent with the evolved mechanism, but consistent with genetic or environmental G protein-coupled receptor kinase factors that both predispose fathers to leave the family unit and predispose daughters to early sexual maturation. This and many other evolutionary hypotheses involving the effects of childhood environmental factors

(e.g. low socioeconomic status) on later behavior (e.g. adult risk-taking [23]) continue to be tested without controlling for genetic and familial confounds, and their conclusions generally suffer from similar (often unacknowledged) alternative explanations. In the previous section we described how behavioral genetics methods can inform evolutionary hypotheses about species-typical or sex-typical human behavioral features. However, the existence of underlying genetic variation itself also requires evolutionary explanation. In this section we focus on how to investigate the evolutionary bases of genetic variation in behavior, and some of what we have learned thus far. The observation of pervasive genetic variation in fitness related traits is at odds with the traditional interpretation of Fisher’s Fundamental Theorem [24]. Explaining the evolutionary basis of such widespread genetic trait variation has been a central question in biology for decades [25], but, in part due to the rapid advances in technology, this question has only recently drawn significant attention in psychology and psychiatry.