Birds do it, bees do it, and men do it any old time. But women will only do it if the candles are scented just right -- and their partner has done the dishes first. A stereotype, sure, but is it true? Do men really have stronger sex drives than women?

Well, yes, they do. Study after study shows that men's sex drives are not only stronger than women's, but much more straightforward. The sources of women's libidos, by contrast, are much harder to pin down.

It's common wisdom that women place more value on emotional connection as a spark of sexual desire. But women also appear to be heavily influenced by social and cultural factors as well.

"Sexual desire in women is extremely sensitive to environment and context," says Edward O. Laumann, PhD. He is a professor of sociology at the University of Chicago and lead author of a major survey of sexual practices, The Social Organization of Sexuality: Sexual Practices in the United States.

Here are seven patterns of men's and women's sex drives that researchers have found. Bear in mind that people may vary from these norms.