Man & Marriage

Man's genetic instinct focuses on availability and fertility so as to spread his genes more widely, while a woman's genetic interest is to find, and keep, the best-quality man she can whose fitness and resources will improve the survival chances of her children.

But for men "mate guarding" -- that is preventing other males from impregnating their mate -- may be a more efficient strategy than promiscuity in many circumstances, and might account for the invention of the institution of marriage. Remarking that human fertility is low, taking on average 120 occasions of regular intercourse to get pregnant, Angier suggests that a man has a choice of two equally effective strategies: he can sleep with a lot of women (the quantitative approach) or he can sleep with one woman for months at a time, and be madly in love with her (the qualitative approach).