My first course in social psychology in 1972 or 1973 was with Elliot Aronson, a premier social psychologist of his era. He mesmerized the class. The first edition of his book The Social Animal had just been published and it was our textbook for the course. My most vivid memory was learning about cognitive dissonance theory and T-groups (then popular Sensitivity Training Groups). Elliot was a big proponent of both. In front of a class of several hundred, he would hold up his book and ask: “Doesn’t it read like a novel?” The class burst into applause. Some women shouted out “We love you Elliot!” He an extraordinarily charismatic lecturer, setting a high bar that was only exceeded in my experience when I heard Phil Zimbardo give a lecture in a class I was a T.A.-ing for his wife, Christina Maslach at Berkeley. During that guest lecture, students broke into applause several times during the lecture, and thunderously at the end. With these introductions to social psychology, nothing seemed more fascinating to me than social interactions and the prospect of uncovering our underlying social psychological machinery.

Historically, psychology has been characterized by a dichotomy between branches that focus on human nature and those that focus on individual differences. Initial “grand theories” of personality, such as those advanced by Freud, Maslow and others, were interested in universal psychological features. For Freud, the emphasis was on sexual and aggressive “instincts” and a universal sequence of psychosexual stages. For Maslow, the focus was on a hierarchy of universal psychological needs, from immediate physiological demands to “self-actualization.” Historically, personality psychology has been the primary branch that has aspired to such broad conceptualizations of human nature.

Ask a few people to describe their ideal partner and you will get the same response every time: a thoughtful pause followed by a deluge. Our partners must be kind, intelligent, and physically attractive. They should be in good health, good with people, good parents, and good providers. Some of our ideals are very specific: straight hair, freckled, with a gap between their front teeth. Others are more abstract: loyal, creative, passionate, and driven. Many ideals are almost contradictory: spontaneous but reliable; flexible but strong-willed; youthful but responsible. Humans seem picky when it comes to mate choice

And this pickiness makes great sense from an evolutionary perspective. For humans, a mate represents a potential reproductive partner, a parenting partner, a cooperation partner, and more. Throughout human evolutionary history, who an individual selected as their mate would have had profound impacts on their reproductive success.

“Love is blind,” according to a common saying. “Love is a recent invention, a mere few hundred years old,” some social scientists have argued. “Love is limited to Western cultures,” according to others. This chapter explains why all these beliefs are radically wrong. From an evolutionary perspective, love is an adaptation, or more accurately a complex suite of adaptations, designed to solve specific problems of survival and reproduction.

My research obsession with mating started in the early 1980s. I sought to test several evolution-based hypotheses that derived from Darwin's 1871 theory of sexual selection. Darwin observed that many qualities of animals seem to have no survival advantage whatsoever. Think about the brilliant plumage of peacocks, the bulky antlers of male deer, or the loud mating croaks of frogs. Darwin's theory of sexual selection identified two critical causal processes by which these weird survival-impairing characteristics could evolve: preferential mate choice, and same-sex competition. Potential mates possessing qualities desired by one sex have a mating advantage; they get chosen, while those lacking desired qualities do not. Qualities linked with winning same-sex competitions also evolve, or get passed on in greater numbers, because victors gain increased sexual access to members of the opposite sex. I became fascinated with these causal processes of sexual selection. It struck me as awe-inspiring that so much evolutionary action revolved around mating, even though many erroneously see evolutionary theory as all about survival.

There were two problems. First, back in the 1980s I was not aware of any psychologists who actually used evolutionary theory to guide their empirical research. Second, although biologists were using sexual selection theory to make discoveries about insects and birds, next to nothing was known about these processes in humans. So I set out to test a few hypotheses about gender differences in the content of mate preferences – that men would prefer fertility in a mate, such as cues to youth and health; that physical appearance provides this bounty of cues; and that women would prefer potential mates who have resource-acquisition potential, in part to offset their large obligatory investment of a nine-month pregnancy (none of this is conscious, of course).

The results supported these predictions, but there was another problem. If the hypotheses anchored in sexual selection were correct, they should be universal, not just found among a couple of undergraduate samples. Over the next five years, I launched the International Mate Selection Project, and ended up assembling a team of fifty collaborators in thirty-seven countries occupying six continents and five islands. I knew that whatever I found would be controversial.