Although there are gender differences in certain behaviors, these are often less than ½ or even ¼ the magnitude of the gender differences in height (in terms of standard deviations) (Hines, 2004). Differences between the behavior/personality of men and women have been documented in assertiveness, anxiety, predjudice, risk taking, aggression, task-orientation, social-emotional orientation, non-verbal communication, attitudes towards relationships and intercourse, verbal ability, visual-spatial ability, self concept, and emotional expression (Lippa, 2002).

Some studies have suggested that that the likelihood of shared sibling homosexuality increases with the degree of relationship (52% in identical twins, 22% in fraternal twins, and 11% in adopted siblings) while other studies failed to show this effect (Rogers, 2001).

There is evidence that sexuality is inherited differently in men and women. High degrees of homosexual attraction are more common in men while low to moderate degrees of homosexual attraction are more common in women (Bailey, 2000). The chromosomal region Xq28 has been associated with variations in male (but not female) sexuality in some families (Hamer, 1993). Maternal immunization may be a determinant of male sexuality which would explain the frequency of homosexual males with older brothers (Hatfield, 2006). Family studies of female sexuality suggest that homosexuality in women is can be familial and may be related to male homosexuality (Bailey, 1993).

A number of studies have indicated a difference between brain regions of heterosexual and homosexual men. Some hypothalamic regions are larger in homosexual men than in heterosexual men (such as the surpachiasmatic nucleus and anterior commissure) while other regions are smaller (the nucleus of the anterior hypothalamus-3) (Kruijver, 2001). In homosexual men, the anterior commissure is larger than in both heterosexual women and men, although it is closer to the size of the region in women. This brain region is not directly involved in sexual behaviors (Allen, 1992). Homosexuality seems to be correlated with other biological traits such as dimorphisms in brain regions such as the third institial nucleus of the anterior hypothalamus and the corpus callosum which differ between homosexual and heterosexual men. Homosexual men have been shown to utilize their hemispheres during verbal and spatial tasks in a pattern more similar to women than to heterosexual men. Homosexuality has also been correlated with dermal ridge patterns and a higher frequency of left-handedness (Lalumiere, 2000).

Exposure to androgens may be a factor determining sexuality in women. The percentage of women who are bisexual or homosexual is higher among those whose mothers were treated with the synthetic estrogen DES (diethylstilbestrol) during pregnancy (a practice which was discontinued in 1971 because of increased cancer risk) (Meyer-Bahlburg, 1995). CAH and DES women are more likely than control women to be homosexual or bisexual (Hines, 2004).

Sexuality in women is thought to have at least some biological roots given studies on behavior of children and even physical characteristics. Some studies have concluded that lesbians differ from heterosexual girls in their childhood play. Differing relationship roles taken by lesbians seem to be correlated with other factors such as waist-to-hip ratio, recalled childhood behavior, the desire to start a family, and testosterone levels (Singh, 1999).


Although studies have attempted to link other variations in sexual behavior to hormonal differences, there is no known endocrine basis for paraphilia (Gooren, 2002).

In rodents, copulatory behavior can be transformed to that appropriate for the opposite gender by hormonal manipulation (Gooren, 2002).