A number of researchers have suggested that evolutionary pressures resulted in different reproductive strategies for men and women. In other words, the best way to pass genes onto the next generation may be different for men than for women. Men can reproduce quickly with little cost in time or energy. However, they have less control over the outcome of their mating, whether their offspring will grow to sexual maturity and be able to pass their genes onto the next generation. Thus, it is in their evolutionary interest to hedge their bets and spread their genes as widely as possible, particularly with females who show “fertility markers,” such as youth and beauty. Women, on the other hand, put tremendous time and energy into reproduction, through pregnancy, lactation, and child rearing. It is in their interest to mate with fewer men and be more selective in their choice of a mate, focusing on the resources he can provide for child rearing.

This model, which is often referred to as the theory of sexual selection, has received considerable empirical support. For example, in a 1989 study by David Buss, 10,000 men and women across thirty-seven different cultures were interviewed about what they looked for in a mate. Men stressed physical attraction and women stressed high status, wealth, and ambition. Moreover, studies show that both homosexual and heterosexual men are more likely to engage in promiscuous and casual sex than either heterosexual or homosexual women. In fact, homosexual men are more likely to engage in promiscuous sex than heterosexual men, presumably because the sexual behavior of heterosexual men is limited by the preferences of their female partners.