The Lay of the Land

The clitoral shaft varies in length from individual to individual. Estimates suggest that it can run from two to three inches, to a pump-assisted five-and-a-half inches.

In 1998, Dr. Helen O'Connell redefined the clitoris. She and her colleagues discovered a large interconnected set of organs. The tip of the clit was just that -- O'Connell found a structure that wrapped around the vagina and urethra -- a body, two arms, and mass of erectile tissue called bulbs, that become turgid on arousal. The bulbs may explain the so-called G-spot.

Fact: The clitoris is located above the vagina, indeed far enough away that it is not directly involved in intercourse. Only one other species of primate, the bonobos, has a similar placement.

Fact: Unlike in most primates, the human vagina tilts backwards and up, facilitating face-to-face intercourse.

Fact: Human females do not signal fertility. In other species, sexual readiness is related to estrus -- the period of peak fertility when sex will do some reproductive good. Signals vary from genitals turning bright red (baboons) to pheromones.

Corollary: Species that signal fertility tend to have sex only during that time. It's called sexual honesty. Bonobos, the primate that shares 98 percent of our genetic code, do not clearly signal fertility, and indeed, have sex well to either side of ovulation. Human females have no signal, and are receptive to sex whenever -- or not.