VIII. Captured in terminology: Sex, sex categories, and sex differences

Swayed by the clear distinction between male and female genitalia, the question of how far these categories extend into human biology has attracted humans for centuries. This question is sometimes being framed as whether the effects of sex are restricted to the genital organs or penetrate the entire organism. Here I argue that the two questions are not equivalent and that whereas the answer to the question, how far sex penetrates the body, is – deep down to the level of every cell, the answer to the question, how far the categories, ‘‘male’’ and ‘‘female’’, do, is – probably nowhere beyond the genitals. That the two questions are often used interchangeably reflects the prevailing conceptualization of sex as a dichotomous system or process that exerts profound effects on other systems (e.g., the brain), leading to sexual dimorphism (i.e., two forms, male versus female) also of these systems. Here I discuss the question of whether the effects of sex result in dimorphic systems, focusing on the case of sex effects on the brain. I show that although there are sex/gender differences in brain and behavior, humans and human brains are comprised of highly variable ‘mosaics’ of features, some more prevalent in females, others more prevalent in males.