Civilization is at war with nature. That is true at least with regard to facial hair. In the heat of this centuries-long battle, on which billions of dollars are spent each year, few have paused to consider how the war began in the first place. Why did nature give men—and some women—beards? How did they end up with a band of hair on their cheeks and chins that society requires they scrape off every day? If one hopes to discover the meaning of beards, it makes sense to start with these basic questions. And that will require us to peer into the mists of the evolutionary past.

It is tempting to think that beards are a holdover from our much hairier progenitors, that for whatever reason, this trait survived as we developed into the naked ape. Yet bonobos, our closest relative in the animal kingdom, lack hair around their mouths—precisely where the human beard grows. It would seem that, if anything, human beings have added hair to their faces, even as they lost it most other places. Even if our ape ancestors had had hairy faces, a question would remain: Why did women lose this hair while men retained it? As it is, a hairy chin and upper lip are virtually unique to the human male.

Beginning with Charles Darwin himself, evolutionary theorists have pondered the origins of the beard. In The Descent of Man (1871), Darwin described a process of sexual selection that operates in tandem with natural selection in shaping the course of human development. Natural selection changes a species by favoring individuals with traits that enhance their chances of survival and procreation. When it comes to procreation, however, there is another level of selection as individuals within a species compete with one another for the favor of sexual partners. Darwin reckoned that, for the purposes of this competition, animals evolved many secondary sexual characteristics that functioned either as weapons to defeat sexual rivals, such as horns or tusks, or as ornaments to attract potential mates, such as colored hair and feathers. Individuals with the more appealing ornaments or stronger weapons would succeed in reproducing themselves and propagating their distinctive traits. Darwin assigned the human beard to the category of ornament, and imagined that it had the power to attract women. Over the millennia, the theory goes, bearded men were more successful in procreation than their smoother competitors, and the human beard evolved into its present form. In short, men now have beards because our prehistoric female ancestors liked them.

But Darwin saw a problem with this idea. Anthropologists of his day reported that human populations varied widely in the fullness of the male beard. It was believed that Native Americans, for example, were nearly incapable of growing them. Darwin surmised that some ancestral women in some particular places must not have liked the beard and because of that prejudice continually selected against it. That is, the beard functioned as an ornament only among peoples who in fact considered it to be an ornament. To help resolve this conundrum, Darwin invoked still another evolutionary process: the inheritance of acquired characteristics. Before Darwin, Jean Baptiste Lamarck had argued that species change over time by passing along newly acquired traits to their offspring. If a giraffe, for example, spends a lifetime stretching its neck to reach food in the treetops, its progeny will be born with longer necks.

Though many a schoolteacher or professor might dismiss the inheritance of acquired characteristics as un-Darwinian, Darwin repeatedly invoked this this principle in The Descent of Man, and did so again on the matter of beards. Noting anthropological observations of peoples who were relentless in plucking unwanted facial hair, and referring to (very dubious) experiments that appeared to show that surgical alterations in animals could be passed on to the next generation, he concluded that “it is also possible that the long-continued habit of eradicating the hair may have produced an inherited effect.” In other words, men who cut or pulled their facial hair would beget boys who grew less facial hair as adults. The inheritance of acquired characteristics thereby completed a process begun by sexual selection, leaving some groups of men with great thick beards and others with almost none. This analysis assigned women a great deal of influence over beard evolution: they chose more or less bearded men according to their tastes, and men plucked their hairs to accommodate them, which in turn led to permanent physiological changes.

By making the evolution of beards a matter of taste rather than survival, however, Darwin failed to provide a truly Darwinian explanation, that is to say, an answer based on the process of natural selection. In fact, his tactic raised more questions that it answered. What made the beard a strongly attractive ornament for some but loathsome to others? If it was simply a matter of taste, why were the passions it stirred strong enough to cause some prehistoric women reject would-be mates? Was it simply a matter of vanity? In the face of such questions, evolutionary biologists after Darwin had their work cut out for them.

As it now stands, theorists have proposed three basic solutions to the beard conundrum. The simplest, which Darwin himself considered and rejected, is that beards have no purpose at all. Accidents happen in evolution as in everything else. A gene preferred in natural selection for, say, its role in making the skin more resilient, may have the secondary effect, not in itself significant, of giving that skin a certain color. The difficulty in discerning any obvious survival value in facial hair makes it a possible example of this phenomenon. But most scientists have been reluctant to let it rest there. For one thing, insignificance is an unprovable supposition. It is impossible to say for certain that beards are simply along for the ride, at least not until all the functions of all the human genome are discovered. Scientists seek reasons for things, after all, and it is far more interesting to suppose that beards serve a purpose, obscure though it may be.

A second possible solution builds on Darwin’s idea that beards are ornaments that charmed prehistoric women and can presumably still charm women today. Adherents of this line of thought have worked to replace Darwin’s reliance on vague notions of taste with more concrete psychological and biological explanations for women’s preferences. A third theory takes the opposite approach, arguing that hair is a threat device useful in intimidating rival males and establishing dominance. Women, then, have been attracted, not to the beard as such, but rather to the social dominance that impressively bearded men achieve over other men.

The challenge for scientists is to figure out ways to test these competing theories. How can one tell if the beard functioned in the evolutionary past more as a lure to females or as a threat to males? One approach is to observe the role of analogous, sex-related ornamentation in animals—feathers, ruffs, antlers, and so forth. Another is to test male and female reactions to bearded faces to see if there are still echoes of the primitive impulses that motivated our ancestors thousands of years ago.

Charles Darwin failed to provide a Darwinian explanation for the beard. Henry Guttmann / Getty Images

In the past five decades, dozens of experiments have charted impressions and reactions to different sorts of male faces in order to assess stereotypes and biases involved in selecting sexual partners, spouses, employees, or political candidates. All have shed light on the beard-as-ornament theory. There is a nearly unanimous finding that a beard makes a significant difference in both men’s and women’s initial perceptions of a man. A beard almost always made a man appear older and more masculine. But does it also make him more attractive? On this matter, studies have reached contradictory conclusions, depending on the subjects tested and the way the questions were asked. Sometimes the beard was deemed very attractive, sometimes very much not so.

A University of Chicago study published in 1969 established that both men and women found bearded men more attractive than shaved men. A few years later, however, students at two other Midwestern universities rated bearded men (in photographs) to be less kind, good, and handsome than beardless men. Soon after, undergraduates in Tennessee and California affirmed the original Chicago findings, assigning bearded men higher marks for maturity, sincerity, generosity, and good looks. Such contradictory findings inspired researchers at the University of Wyoming to conduct a survey that simply asked undergraduate women straight out whether they preferred men with facial hair. Of the 482 women who filled out a questionnaire, only 17 percent favored beards, while many expressed their outright distaste; about 42 percent liked mustaches.

By the late 1970s, the count stood at two studies in favor of, and three against, the desirability of beards. This back-and-forth continued for the next two decades—with a few split decisions. It is safe to say that anyone hoping to find decisive evidence for the beard-as-ornament theory faced frustration. Inconsistent lab results are the product of differing methods and conditions but may also reflect the triumph of nurture over nature, which is to say, our cultural preferences have overwhelmed residual primitive instincts that promoted the evolution of beards.

If civilization rather than evolution ultimately determines the meaning of hair, it should be possible to formulate a sociological theory of beards. Many have tried to do so. Some have taken a Freudian approach, in which hairstyles and hair rituals derive their power from expressing or suppressing the libido. Others investigators have theorized about the use of hair and beards in establishing social and gender distinctions; these ideas have managed to explain many, though not all of the uses of hair in social communication.

Recently, French anthropologist Christian Bromberger acknowledged social scientists’ failure to explain the meaning of hair. As an expert in Middle Eastern anthropology, Bromberger was intrigued by the ways in which, from the tenth century to the present day, Muslims and Christians have differentiated themselves through facial hair, as have Latin Christians from Greek Christians. Bromberger knew it was more than this, however. Hair could also help define male and female, distinguish conformists from dissenters, and indicate contrasts between refined civilization and primitive naturalism. What he recognized in all of this complexity was unfinished business. He called for the study of “hairology” that would map contrasting attributes of hairstyles—artificial/natural, long/short, hirsute/ hairless, light/dark, smooth/nappy—and the social oppositions they were meant to indicate. Such a hair dictionary, as it were, would serve to translate a wide range of explicit and implicit social messages.

The dream of hairological theory is a pleasant one, but it will not easily be achieved. Even if the detailed patterns of affinity and opposition were worked out for a given society, it would provide at best a kind of snapshot of social codes. It would capture a moment in the ebb and flow of human history, but not the ebb and flow itself. In fact, the meaning of facial hair is most visible in change rather than stasis. Watching the film from beginning to end is the only way to understand the plot that drives events. The same is true of the history of facial hair. Following the twists and turns of the unfolding story of beards, shaving, and manliness casts new light on both the past and the present, allowing us to read the conscious and unconscious messages we send with our hair.