Man and Woman, Casual Sex and Jealousy: Insight from the Field of Evolutionary Psychology

'Our modern skulls house a stone age mind."

Cosmides and Tooby, 1997

If questioned today, many people might agree with what seems to be an illogical coupling of statements: (1) A man is more likely than his female mate to feel comfortable about having casual sex with multiple partners, but (2) the same man is likely to feel jealous about his mate having sex with someone else. Yet, when the underlying causes for a male's apparently inconsistent behavior are explored from the perspective of evolutionary psychology, a logical explanation emerges.

Evolutionary psychology is a branch of study focused on the problems and stress factors that ancestors of humans faced, the "psychological mechanisms" that natural selection developed to address these problems and stresses, and the ways in which these ancient mechanisms work today (Crawford and Anderson, 1989, cited in Crawford and Salmon, 2004). Evolutionary psychology focuses on those "affects, cognitions and behaviors" which helped ancestors of humans to solve "some adaptive problem in the ancestral environment" (Kruger, 2002).

To arrive at an explanation for a man's tendency to feel more comfortable about having...

Women produce only a few, but energy-rich, gametes (i.e. eggs), into which they invest a significant amount of physical resources and time from conception through birth and nursing. A woman requires stability to be successful in this endeavor. She is careful in her selection of a mate who can offer the protection and support she needs, focusing on quality over quantity in her mate. A man, on the other hand, produces many, but energy-poor, gametes (i.e. sperm). He has much less of a physical investment in his offspring. A man, unlike a woman, focuses on quantity of mates rather than relationship quality because, if he has multiple mates, he increases the odds that he will father numerous offspring, thereby helping to ensure the transmission of his genes to successive generations. (Looy, 2001; Wright, 1994) From the perspective of evolutionary psychology, the desire of the man to maximize chances of transmitting his genes to future generations when compared to the woman's desire for stability helps to explain why a man may feel more comfortable about having casual sex with multiple partners than does his female mate.
Evolutionary psychologists seeking to…