A number of sex differences exist in the physical structure of the brain (review by Kimura, 1999). The hypothalamus, a clump of nuclei at the base of the brain that mediates a variety of sexual behaviors (Kimura, 1999, p. 130), differs between the sexes. Androgens appear to affect parts of an area called the interstitial nuclei of the anterior hypothalamus (INAH), which is larger in men than in women, and larger in heterosexual men than in homosexual men (LeVay, 1991). Though this suggests that the hypothalamus and its development may be involved in sexual preferences, of course the data are simply correlational. Similarly, the anterior commissure (probably involved in sharing information between the brain's hemispheres) is larger in women and homosexual men than in heterosexual men (Allen and Gorsky, 1991).

Male brains are 10-15% larger than female brains, and have more cortical neurons than female brains (Kimura, 1999, p. 128), in part related to sex differences in spatial ability (see below). Because men are physically larger than women, the brain-body weight ratio is roughly equal between the sexes (Ankney, 1992; Kimura, 1999, p. 128). Interestingly, so far, brain sex differences related to sexual selection (e.g., spatial differences, see below) tend to be significantly different. Other differences (e.g., in the United States, men have a nonsignificant ~4-point advantage on IQ tests) tend to be nonsignificant—the distribution of the traits may differ between men and women, but we find no systematic or significant differences.

Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

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