Sex differences in humans .January 13, 2021
Sex differences in humans have been studied in a variety of fields. In humans, biological sex consists of five factors present at birth: the presence or absence of the SRY gene (an intronless sex-determining gene on the Y chromosome), the type of gonads, the sex hormones, the internal reproductive anatomy (such as the uterus), and the external genitalia. Sex determination occurs solely by the presence or absence of a Y chromosome. Phenotypic sex refers to an individual’s sex as determined by their internal and external genitalia, expression of secondary sex characteristics, and behavior.
The sex of the individual can be defined in different ways, giving rise to different conceptual frameworks about what determines sex. Sex differences generally refer to traits that are sexually dimorphic. A subset of such differences is hypothesized to be the product of the evolutionary process of sexual selection.
Sex differences in medicine include sex-specific diseases, which are diseases that occur only in people of one sex; and sex-related diseases, which are diseases that are more usual to one sex, or which manifest differently in each sex. For example, certain autoimmune diseases may occur predominantly in one sex, for unknown reasons. 90% of primary biliary cirrhosis cases are women, whereas primary sclerosing cholangitis is more common in men.
Sex differences in human physiology are distinctions of physiological characteristics associated with either male or female humans. These can be of several types, including direct and indirect, direct being the direct result of differences prescribed by the Y-chromosome (due to the SRY gene), and indirect being characteristics influenced indirectly (e.g., hormonally) by the Y-chromosome. Sexual dimorphism is a term for the phenotypic difference between males and females of the same species.