She's not physically attracted to him, nor does she want to be romantically involved. So she decides she will go home with her friend—to show him how it's done. I wanted to experience physical pleasure. Meston and colleague David Buss first questioned men and women — ranging in age from 17 to 52 — to come up with a list of distinct reasons people have sex. We hear from women who've had sex to boost their confidence, even if it's with a man or woman they find repulsive, and from those who've used sex to barter for gifts or household chores 9 percent of us have used this form of economic sex, according to a University of Michigan study. Since her study came out Tuesday, people are coming up with new reasons to have sex. No wonder things get complicated. As she undresses, she feels powerful and sexy—and that feeling not the presence of her soon-to-be deflowered friend turns her on. I wanted to give someone else a sexually transmitted disease. Goldstein, who wasn't part of Meston's study, said the Texas research made a lot of sense and adds to growing evidence that the vaunted differences in the genders may only be among people with sexual problems. In their new book, Why Women Have Sex , University of Texas psychologists Cindy Meston and David Buss aim to illuminate the complexities of women's sexual motivations through women's own words—an important step, they say, to better understanding how women can achieve sexual satisfaction. Forget thinking that men are from Mars and women from Venus, "the more we look, the more we find similarity," said Dr. I wanted to break up my relationship. I was "in the heat of the moment. I wanted to express my love for the person.