Sexual Anatomy
The theory of sexual selection has been used to explain a number of human anatomical features. These include rounded breasts, facial hair, pubic hair and penis size. The breasts of primates are flat, yet are able to produce sufficient milk for feeding their young. The breasts of non-lactating human females are filled with fatty tissue and not milk. Thus it has been suggested the rounded female breasts are signals of fertility. The evolutionary biologist Richard Dawkins has speculated that the loss of the penis bone in humans, when it is present in other primates, may be due to sexual selection by females looking for an honest advertisement of good health in prospective mates. Since a human erection relies on a hydraulic pumping system, erection failure is a sensitive early warning of certain kinds of physical and mental ill health.
Homo also has by far the largest penis of the great apes, and this may be sexually selected in much the same way as the larger testicles of Pan. It has been suggested the evolution of the human penis towards larger size was the result of female choice rather than sperm competition because sperm competition generally favors large testicles and a small penis, as in the chimpanzee. However, penis size may have been subject to natural selection, rather than sexual selection, due to a larger penis' efficiency in displacing the sperm of rival males during intercourse. A model study showed displacement of semen was directly proportional to the depth of thrusting, as an efficient semen displacement device.
Read more about this topic: Sexual Selection In Human Evolution, Sexual Dimorphism
Famous quotes containing the word anatomy:
“But a man must keep an eye on his servants, if he would not have them rule him. Man is a shrewd inventor, and is ever taking the hint of a new machine from his own structure, adapting some secret of his own anatomy in iron, wood, and leather, to some required function in the work of the world. But it is found that the machine unmans the user. What he gains in making cloth, he loses in general power.”
—Ralph Waldo Emerson (1803–1882)