C'mon ... tell us the truth.

Dr. Wendy Walsh: A new book by renowned evolutionary psychologist Dr. David Buss and psychologist Cindy Meston called Why Women Have Sex gives some astounding answers. The book is a compilation of the results of a three-year study that asked more than 1,000 women why they have sex. They were asked to choose from a list of 237 possible reasons. Two-hundred and thirty-seven. We are nothing if not complicated.

One of the most interesting points is that women have a much wider range of reasons than men for having sex. Makes sense, considering that historically, men need only to look for reproductive fitness -- something that is very visual -- in order to plant their seed. Women, on the other hand, have much higher risks when they choose to engage in sex -- like pregnancy, disease, and, oh yeah, starvation if the guy can't bring home a woolly mammoth. So women traditionally needed to look further than tans and biceps to choose a baby-daddy.

In modern times when medicine, birth control, and a female's own income can reduce the risks associated with sexual intercourse, there is now much more choice for women. According to the book, the reasons women have sex might include marital duty, an adventure into another ethnicity, an effort to "get rid" of her virginity, or an attraction to a sexy brain. Unlike men, who have far more pressure to mate according to physical cues, women may even mate with men who are not classically (symmetrically) physically attractive. Women may become aroused by personality, humor, self-confidence, and social status, among other things.

The book also talks about how a woman's perception of sex can change over her lifespan. For instance, the sexual double standard may affect a young woman's choice less than an older woman. As the mother of a friend of mine likes to remind us, "Darling, you girls are much too old to have a reputation."

One other interesting fact is that men's reports of feelings of arousal pretty much match their physical outcome -- i.e., sexy thoughts upstairs equal blood flow downstairs. However, women are far more interesting (but we knew that!). Women may report being sexually aroused even when monitors inside their vagina reveal no activity. Yes, ladies, sometimes it's all in our heads.

The book Why Women Have Sex by Drs. Buss and Meston is available now.

Dr. Wendy Walsh holds a Ph.D. in Clinical Psychology and her area of interest is Attachment Theory, a psychological, evolutionary and ethological theory that provides a descriptive and explanatory framework for understanding interpersonal relationships between human beings. As a psychological assistant registered with the California Board of Psychology, Dr. Walsh has treated individuals, couples and families for a variety of mental health concerns including personality disorders, anger management, eating and substance disorders, and depression. Connect with Dr. Walsh on Facebook.