Heterosexuality
From Encyclopedia of Sex and Sexuality
The human species has evolved to be heterosexual—that is to reproduce through the mating of males and females. No one knows exactly how two separate sexes evolved, but millions of years ago individuals of two complementary strains appeared, followed by the emergence of two distinct sexes—one carrying eggs, the other, sperm. These were our sexual ancestors, the forbears of human heterosexuality.
While other species have elected alternative methods of reproduction, humans have succeeded through a complex system of male/female bonding. In strictly biological terms, heterosexual reproduction has a number of advantages, the principal one being that it allows for greater variability in the species. While asexual reproduction most often produces offspring that are identical to the parent, sexual reproduction produces individuals that reflect the traits of two distinct parents. Over generations, this constant mixing and re-mixing of the genetic pool produces a species of tremendous adaptability. So humans evolved to be men and women and they must mix their genes or become extinct.
The necessity of coming together sexually in order to reproduce has led to an amazingly complicated system of mating. A woman and man must send off sexual signals to each other, must feel attraction, and must be attractive. Beyond this, they must feel compelling sexual emotions as reasons to invest time not only in sex but in pair-bonding as well. Pair-bonding is a hallmark of the human animal, a clever strategy for the rearing of defenseless young. It is a basic principle in heterosexual culture. When a woman and man fall in love, coupling is a norm. This is the human way, governed by culture, but also determined by our heterosexual biology as the way to best propagate our species.
For all heterosexual animals the reproduction game begins with sexual attraction. Humans are no exception. Accordingly, men and women have evolved very specific anatomies, instincts, and behaviors. Body shape, stature, hair, odors, and sensuously reddened lips function as gender flags, designed to entice a prospective mate. While Charles Darwin was aware that sexual selection could not account for all sexual traits, the eternal struggle of heterosexuality—to decide who will mate and breed with whom—is the most likely explanation for our most seductive and alluring anatomy.
Women’s breasts, for example, are uniquely human and their size is completely unnecessary for the sole purpose of nursing. Ethnologist Desmond Morris proposes that they function as sexual bait. Other physical aspects of human sexuality emerged as our ancestors jockeyed for prized mates. As they emerged, behaviors evolved to make the most of our capacities to attract. Why do women, not men, wear lipstick? Why do men expand their chests when they are attracted to a woman? Why is it still a general rule that women flaunt their looks while men impress with money and social status? While there are many men and women who do not follow these patterns, much of our courting behavior may be governed by instincts of which we are not aware.
One of the greatest biological determinants of human heterosexual interaction is the female’s continuous state of sexual receptivity. To males and females of almost any other living species, sex is not constantly available. The females of most species have a period of heat, or estrus, and when they are not in heat they generally refuse to accept the male. Human females can, if they wish, copulate at anytime. In practice, this biological imperative has led to an entire matrix of flirting, with complex customs, rules, and protocols both women and men understand and employ. Smiles, gazes, a toss of the head, the arch of the eyebrow—these actions are the grammar of a very rich language, a vocabulary that defines us as sexual beings.
Perhaps the most human quality of sexuality is our capacity to fall in love. Scientists point out that this, too, is rooted in biology; the emotions that encourage and even compel us to bond and to fall in love are physiologically ordered to a surprisingly large extent. What are these emotions which drive us to couple? In love, humans experience a panoply of feelings. But the twin locomotives of human pair-bonding are first, infatuation and then, emotional attachment.
There is evidence to suggest that infatuation is chemically triggered by the limbic system of the human brain. The limbic system governs our most basic, primitive emotions—fear, rage, joy, love, and hate. It is almost certain that the storm of infatuation is similarly jump-started by that part of the brain. The extraordinary euphoria and hyperenergy of attraction are caused by a brain bath of natural amphetamines in the emotional centers of the brain. This may be why our craving for romantic love is so intense; why we risk the emotional roller-coaster of falling in love.
Sexual infatuation seems to have a very natural life expectancy, and its waning enables another emotion to emerge—attachment. This is, perhaps, the most elegant of human feelings, that sense of contentment, of sharing, of oneness with another human being. In the attachment state of love, the brain begins to stimulate production of endorphins, the opiates of the mind. A relationship during the attachment phase is no longer turbulent; it is stable. The man and woman who were driven together by sexual attraction and romatic love stay together because of their strong affectional and loving bonds.
Humans are a heterosexually reproducing species, designed, as all organisms are, to procreate. Sexual union gives them the means to achieve great variety, and the sexual chemistry of their species may provide the incentive.
