A couple of weeks ago, I shared Reinius and colleagues’ 2008 article, “An Evolutionarily Conserved Sexual Signature in the Primate Brain” with our group. The study compared gene expression in the occipital cortex of males and females from three primate species. The species were selected for their morphological sexual dimorphism: humans (Homo sapiens) and cynomolgus macaques (Macaca fascicularis) are sexually dimorphic, whereas common marmosets (Callithrix jacchus) are relatively sexually monomorphic. More than one hundred genes with sex-biased expression in the cortex were identified in humans and macaques, but less than ten such genes were identified in marmosets. Furthermore, 85 of the one hundred sex-biased genes were common to both humans and macaques. From these results, the authors posit that sexual gene expression dimorphism is, to an extent, conserved in primate cortexes.
When I first found this paper, I was terribly excited since it used genetics to compare brain sexual dimorphism across species. Up until now we have focused primarily on human studies, which makes sense since we are a class about human sexual selection, but the “specialness” of humans can only be evaluated if we compare ourselves to other animals. Unfortunately, we had a rough time understanding the technicalities of the methods and statistical analysis, so we started speculating how the observed sexual dimorphism in brain gene expression would translate into behavioral dimorphism. From here the conversation quickly turned to the taboo subject of *gasp* the biological basis of behavioral sexual dimorphism in humans.
Larry Summers resigned from his post as President of Harvard after he suggested that the underrepresentation of women in certain areas of academia was due to different aptitudes between men and women. No one can say that men and women think and act differently because of biology without being reproached, yet the general public is much more readily accepting of the biological basis of behavior in other animals. Granted, the notion of genetics influencing behavior is harder to wrap your head around than the idea of genes shaping morphology. This makes many people uncomfortable. Going back to Summers and the gender-gap in math/sciences…As a discussion group, we think that even though men and women, on average, probably do have different abilities at different subjects, one cannot judge an individual man/woman based on this difference (population statistics!), and the difference is a really small factor of gender disparity in the work place.
