In the recent romantic comedy, “What’s Your Number?” Anna Faris plays a young single woman who is worried that her high number of past sexual partners, 19, will prevent her from meeting Mr. Right, and determines to find lasting love before bedding No. 20. At least she’s being honest. In reality, people often lie about their “number”: Men tend to overestimate, while women generally underestimate. Of course, it’s possible that these men and women aren’t lying at all, but simply remembering incorrectly, or reaching their number according to their own definition of sex - like the Clintonian method, for example. In general, though, there seems to be a double standard. What’s in a number, and why should a woman’s be lower than a man’s? Perhaps we can find the answer in evolutionary psychology. As the standard Darwinian narrative would have it, men possess a nearly inexhaustible supply of “seed” and are motivated to spread that seed in the hope of propagating their specific gene-set as much as possible. So by a “survival of the fittest” sense of logic, perhaps a guy who has not spread himself enough would be viewed, in big-picture evolutionary terms, as less healthy and hence less attractive and mate-worthy to a potential female partner. So in the theoretical mating-market, wouldn’t a woman want to select what other women have previously selected, and wouldn’t those guys with the higher number also potentially have more mate-worthy traits (looks, money, intelligence) than the guy with a lower number? Conversely, by the same logic, that female partner is supposed to be choosier and to have had fewer sexual partners because of the risk of getting pregnant - hence a woman's propensity to diminish her number. But after decades of birth control, should evolutionary factors still trump a current reality in which women can have as many sex partners as they like? Additionally, female humans, unlike most other mammals, have a nearly constant “sexual receptivity," meaning that their sexual interest is not limited to their ovulation period and that ovulation is concealed as opposed to advertised the way it is with other female mammals. Some evolutionary anthropologists would say this state of extended receptivity is really just a way for a particular woman to ensure she can keep a particular man satisfied so he’ll stick around to help with sustaining and protecting the family. In short, her sexual receptivity is a mechanism to limit his number of current sexual partners. But couldn’t it also just be because sex is fun and women enjoy it as much, if not more, than men? Women have the capacity to experience multiple orgasms within a single session of sexual activity, unlike men, who require a refractory period after having sex. As Dr. Emily Nagoski, author of the "Good in Bed Guide to Female Orgasms," notes: "Men experience a post-ejaculatory refractory period, when their bodies do not respond to sexual stimulation and ejaculation is impossible. At ejaculation, a man’s body throws a massive, systemic 'shut off' switch, which effectively puts his sexuality in 'park,' leans back the seat, and turns lulling music on the radio. The hypothesized reason for this phenomenon is that it gives a man’s body an opportunity to begin replenishing the sperm stores spent in ejaculation. Since women don’t ejaculate, no refraction happens. Lack of refraction is a likely reason why multiple and extended orgasms are easier for women than for men.” As women age, they tend to move toward their sexual prime, not away from it, as is the case with men. All this suggests that women have a sexuality that outstrips men. If anything, their number should be equal to or greater than a man’s, perhaps far greater. Those of you up on your ancient Greek mythology will remember that the soothsayer Tiresias, born a man, was turned into a woman for seven years before being turned back into a man. Upon being approached by Zeus and Hera, who were arguing with each other about who enjoys sex more, a man or a woman, Tiresias responded, “Of 10 parts, a man enjoys one only.” Hera took offense at the idea that a woman’s number could be nine times that of a man’s, and struck Tiresias blind. As long as men continue to mythologize their own sexual pasts, while turning a blind eye to the reality of female sexuality, I suppose women will continue to downplay their number. But whether you’re a man or a woman, your sexual history is so much more than just the number of partners you’ve had. It’s who you are and what you bring to those experiences. Your sexual history is the sense of self-esteem and self-respect you bring to your sex life. It’s how you value your sexual identity and the expression, gratification and growth of that identity. So what’s your number? Or your partner’s? Does it matter whose is higher or lower? Your sexual history isn’t just something that happened in the past. It’s something that’s happening right now, with the person lying next to you.