Each of us owes our existence to thousands of generations of successful ancestors. The gulf between the sexes in emotional reactions to infidelity reveals something profound about human mating strategies. BUSS Read the Review The Dangerous Passion Jealousy is not only inbred in human nature, but it is the most basic, all-pervasive emotion which touches man in all aspects of every human relationship. I'm not a big chap or a handsome chap but my wife is so pretty and I don't think I come up to her high standards. A man does not think, "Oh, if my wife has sex with someone else, then my certainty that I'm the genetic father will be jeopardized, and this will endanger the replication of my genes; I'm really mad. Labeling jealousy as pathological simply because a spouse has not yet strayed ignores the fact that jealousy can head off an infidelity that might be lurking on the horizon of a relationship. The fact that women have affairs in cultures from the Tiwi of northern Australia to the suburbs of Los Angeles reveals that some women refuse to limit themselves to a single partner despite men's attempts to control them and despite the risk of divorce if discovered. Shouldn't we love all children equally? From an ancestral man's perspective, the single most damaging form of infidelity his partner could commit, in the currency of reproduction, would have been a sexual infidelity. Were you serious when you told me that? Ancestral women who failed to have mate insurance, a backup replacement in the event that something happened to her regular partner, would have suffered greatly compared to women who cultivated potential replacements. I love you forever. In a hazardous world where rivals lurk, partners harbor passions for other people, and infidelity threatens to destroy what could have been a lifelong love, it would be surprising if evolution had not forged elaborate defenses to detect and fend off these threats. There's a rationality to the irrationality.