Ticking biological clock increases women's libido, new research shows

Such "reproduction expediting" includes one-night stands and adventurous bedroom behavior, the research shows.

In a paper published in the July edition of Personality and Individual Differences, psychology graduate students Judith Easton, Jaime Confer and Cari Goetz, and David Buss, professor of psychology, found that women age 27-45 have a heightened sex drive in response to their dwindling fertility.

In the study the researchers split 827 women into three groups: high fertility (ages18-26), low fertility (ages 27-45), and menopausal (ages 46 and up). The respondents answered an online questionnaire about their sexual attitudes and behavior.

Compared with the other groups, women with low fertility were more likely to experience:

• Frequent sexual fantasies
• Thoughts about sexual activities
• More intense sexual fantasies than their younger counterparts
• A more active sex life and willingness to have a one-night stand
• A willingness to have casual sex

Contrary to their predictions, the researchers found that when comparing low and high fertility women who were in relationships, the older, less fertile group did not fantasize more about someone other than their current romantic partners. Instead they fantasized equally about their significant others and other romantic partners.

According to a 2010 report from the Pew Research Center's Social & Demographic Trends, mothers of newborns in all race and ethnic groups are now older than their counterparts 20 years ago. Fourteen percent of births in 2008 were to women ages 35 and older, and 10 percent were to teens. With more women having children past their peak childbearing years, Easton says she believes the research will have implications on reproductive and sexual health issues, such as fertility, sexual dysfunction and marital development.

"Our findings suggest that women don't need to necessarily go 'baby crazy' in their 30s or go around thinking they're supposed to be having a 'sexual peak,'" Easton said. "Our results suggest there is nothing special about the 30s, but that instead these behaviors manifest in all women with declining fertility. It may be more difficult to conceive past the age of 35, but our research suggests women's psychology will continue to motivate them to try until menopause."

The study outlines for the first time the changes in women's reproductive behavior across the life cycle from an evolutionary standpoint. The researchers attribute these differences to ingrained psychological mechanisms rooted in each gender's adaptive responses over millennia of human evolution.