Sexual deception, the difficulties of attracting viable marriage partners, intimate partner violence, infidelity, mate poaching, divorce, and post-breakup stalking—these diverse phenomena are all connected by a common causal element: an unrelenting shortage of valuable mates. The dearth of desirable mates is something we should worry about, for it lies behind much human treachery and brutality.

Despite the fact that many equate evolution with survival selection, survival is only important inasmuch as it contributes to successful mating. Differential reproductive success, not differential survival success, is the engine of evolution by selection. You can survive to old age. But if you fail to mate, you fail to reproduce, and your genes bite the evolutionary dust. We are all descendants of a ruthless selective process of competition for the most valuable mates—those who can give our children good genes and an array of resources ranging from food and shelter to the social skills needed to scramble up the status hierarchy.

People are uncomfortable placing a value on other humans. It offends our sensibilities. But the unfortunate fact is that mate value is not distributed evenly. Contrary to yearnings for equality, all people simply are not equivalent in the currency of mate quality. Some are extremely valuable—fertile, healthy, sexually appealing, resource-rich, well-connected, personable, and willing and able to confer their bounty of benefits. At the other end of the distribution are those less fortunate, perhaps less healthy, with fewer material resources, or imbued with personality dispositions such as aggressiveness or emotional instability that inflict heavy relationship costs.

The competition to attract the most desirable mates is ferocious. Consequently, those most valuable are perpetually in short supply compared to the many who desire them. People who are themselves high in mate value succeed in attracting the most desirable partners. In the crude informal American metric, the 9s and 10s pair off with other 9s and 10s. And with decreasing value from the 8s to the 1s, people must lower their mating sights commensurately. Failure to do so produces a higher probability of rejection and psychological anguish. As one woman advised her male friend who bemoaned his frustration about his lack of interest in the women attracted to him and the unreciprocated interest by women to whom he was attracted, "you're an 8 looking for 9s and being sought after by 7s."

Another source of problems on the mating market comes from deception. Scientific studies of on-line dating profiles reveal that men and women both try to appear higher in mate value than they truly are on precisely the dimensions valued by the opposite sex. Men exaggerate their income and status, and tack on a couple of inches to their real height. Women present as 10 to 15 pounds lighter than their real weight and some shave years off of their actual age. Both show unrepresentative photos, sometimes taken many years earlier. Men and women deceive in order to attract mates at the outer limit of their value range. Sometimes they deceive themselves. Just as 94% of professors believe they are 'above average' for their department, on the mating market many think they are hot when they're not.

Despite valiant efforts, men's attempts to increase their market value in women's eyes do not always work. Many fail. Dating anxiety can paralyze men brave in other contexts. Some spurned men become bitter and hostile toward women after repeated rejections. As Jim Morrison of 'The Doors' once noted, "women seem wicked when you're unwanted."

Mating difficulties do not end among those successful enough to attract a partner. Mate value discrepancies open a Pandora's box of problems. An omnipresent challenge within romantic relationships derives from mate value discrepancies—when an 8 mistakenly pairs up with a 6, when one member of an initially matched couple plummets in mate value, or even when one ascends more rapidly professionally than the other. Jennifer Aniston's hold on Brad Pitt proved tenuous. Mate poachers lure the higher value partner, driving wide initially small wedges: "He's not good enough for you;" "She doesn't treat you well;" "You deserve someone better . . . like me." Empirically, the higher mate value partner is more susceptible to sexual infidelity, emotional infidelity, and outright defection.

The lower mate-value partners typically struggle mightily to prevent infidelity and breakup. They use tactics ranging from vigilance to violence. Intimate partner battering, abhorrent as it is, has a disturbing functional logic. Since self-esteem is, in part, a psychological adaptation designed to track one's own mate value, blows to self-esteem cause reductions in self-perceived mate value. Physical and psychological abuse predictably harm the victim's self-esteem, narrowing the perceived discrepancy between a woman's and her partner's mate value, and sometimes causing her to stay with her abuser.

Those who succeed in breaking up and leaving are sometimes stalked by former partners—typically men who know or sense that they will never again be able to attract a woman as valuable as the one they have lost. Studies I've conducted in collaboration with Dr. Joshua Duntley reveal that as many as 60% of women and 40% of men have been victims of stalking. Many stalkers are sustained by the false belief that their victims truly love them, but they just don't realize it yet. Stalking, like intimate partner violence, too has a disconcerting functional logic. It sometimes works in luring the woman back.

There is no easy fix for the great shortage of desirable mates. In the undemocratic world of mating, every success inevitably comes as a loss to vying rivals. Every human that conceives can be deceived. Mate poachers will always be ready to pounce. The pleasures of sexual temptation come in the here and now. The costs of infidelity lie in the distant and uncertain future. But perhaps a keener awareness of mate value logic will give us the tools to curtail the more sinister products of the mating wars.