Prenatal hormones and sexual orientation Only 23% of childhood gender problems will result in transsexuality in adulthood. Drawing on some transsexualism cases, Garcia-Falgueras and Swaab state that "[f]rom these examples it appears that the direct action of testosterone on the developing brain in boys and the lack of such action on the developing brain in girls are crucial factors in the development of male and female gender identity and sexual orientation ... ." Countless studies have been run on peripheral levels of sex steroids in male and female homosexuals, a considerable number of which claimed to find "less 'male hormone' and/or more 'female hormone' in
Sexual selection in mammals Sexual selection in mammals Sexual selection in mammals started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, consisting of male-male competition and mate choice that mold the development of future phenotypes in a population for a given species. A good example of intrasexual selection, in which males fight for dominance over a harem of females, is the elephant seal – large, oceangoing mammals of the genus "Mirounga". There are two species: the northern ("M. angustirostris") and southern elephant seal ("M. leonina") – the largest carnivore living today. Both species show extreme sexual