Categories : Secondary sexual characteristics Sexual selection. Charles Darwin hypothesized that sexual selectionor competition within a species for mates, can explain observed differences between sexes in many species. In females, breasts are a manifestation of higher levels of estrogen ; estrogen also widens the pelvis and increases the amount of body fat in hips, thighs, buttocks, and breasts.
Differences in size between sexes are also considered secondary sexual characteristics.
Main article: Sexual selection in human evolution. As puberty begins and sex hormone levels rise, differences appear, though some changes are similar in males and females. The general structure and shape of the body and face, as well as sex hormone levels, are similar in preadolescent boys and girls.
See also: Mate choice. Categories : Secondary sexual characteristics Sexual selection.
These nipples and associated glandular tissues develop after birth as in normal female animals. Sexual differentiation begins during gestationwhen the gonads are formed. Another of Fisher's ideas is the sexy son hypothesiswhereby females will desire to have sons that possess the characteristic that they find sexy in order to maximize the number of grandchildren they produce.
It is concluded that androgens normally prevent the development of nipples and extensive formation of mammary tissue in male fetuses.
In humans, visible secondary sex characteristics include pubic hair , enlarged breasts and widened hips of females, and facial hair and Adam's apples on males. From Wikipedia, the free encyclopedia. Hidden categories: Harv and Sfn no-target errors Webarchive template wayback links All articles with unsourced statements Articles with unsourced statements from October Hormones and Embryonic Development: Advances in the Biosciences.
Sexual characteristics due to combat are such things as antlers, horns, and greater size. Estradiol and other hormones cause breasts to develop in females.