Evolutionarily, having an orgasm was one of the ways that women could tell whether a man would be a good lifelong partner, because it could help women distinguish between a caring, patient male and a selfish or impatient one. Nevertheless, female orgasm can be so subtle that some women don't even know when they've had one. Many of the physical manifestations of a woman's orgasm are designed to help increase the chance that the sperm will find its target and fertilize the egg.
The fact that women can be stimulated to orgasm through not only the genitals, but also the mouth, nipples, and other parts of the body, points to the complexity of the system - and reinforces the fact that the true biology of sex really revolves around the brain. (One theory is that sexual stimuli are carried from the cervix and uterus to the brain through a branch of the nerve called the vagus nerve - one of the nerves stimulated during deep breathing and meditation.)
Find out more about this book:You: Being Beautiful - The Owner's Manual to Inner and Outer Beauty