That high, clear sound was so prized by papal church choirs of late sixteenth-century Italy that it led to a barbaric practice: the removal of young boys’ testicles so that their voices would not change at puberty. The church could have avoided this drastic expedient simply by using girls and women as singers—except that females were forbidden, by canon law, from performing in churches. The boys were usually operated on between the ages of seven and nine. As adults, these singers, known as castrati, had vocal cords that remained small and thin, but their bodies tended to grow close to adult male size.7 This resulted in an unusual hybrid sound: a female pitch, but a male timbre and power. One contemporary writer described the castrati as sounding “as clear and penetrating as that of choirboys but a great deal louder with something dry and sour about it yet brilliant, light, full of impact.”8 A craze for the voice occurred in the mid-seventeenth century with the rise of Italian opera, for which castrati parts were expressly written. At the craze’s peak, an estimated four thousand boys a year were castrated—many of them poor children whose parents gave them over to gelding in the hope that they would become successful singers and lift the family from poverty.9 In 1861, the practice was finally stopped, but castrati continued to be produced, for the private delectation of the pope, in his Sistine Chapel. The last Vatican castrato, Alessandro Moreschi, officially retired in 1913.
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While we know how the human voice becomes sexually dimorphic at puberty, we don’t know exactly why. But given that the differences emerge at sexual maturity, the safe assumption is that it has to do with mating and reproduction.
In The Origin of Species, Darwin said that the successful wooing and winning of reproductive partners involves two quite separate mechanisms: attracting mates through the display of seductive ornaments (like the male peacock’s tail or the finch’s fancy songs), but also driving off, or vanquishing, same-sex rivals. The latter mechanism, which later evolutionary biologists called “contest competition,” almost always involves males battling other males (surprise!) for the favors of females, and this led to the evolution, on male bodies, of what Darwin called “special weapons,”10 including the antlers on stags (who run at each other and butt heads at mating time), leg spurs on roosters (who slash at other males to neutralize them as sexual competitors), and long incisor teeth on male chimpanzees (who flash these fangs at other males when competing over a female). Some evolutionary biologists explain the deepened male voice in Homo sapiens as one of these special weapons. While the voice can’t physically maim or kill, like an antler, leg spur, or fang, it is weaponized in aggressive encounters by a dropped pitch, which creates the illusion of greater body size. Thus, those hominin males who, through a quirk of their genetics, happened to possess larger, thicker vocal cords than the norm, and thus naturally deeper voices, would have had an inborn advantage over males with slightly smaller vocal cords and thus higher voices. Scaring off their squeakier sexual rivals, deep-voiced males won the contest competition for mates, and thus the genes for deep-voiced males were sexually selected in our ancestors. The male voice went south.
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David Puts, a professor of anthropology and evolutionary psychology at Penn State University, has spent two decades exploring the sexual dimorphism of the human voice and has concluded that, in terms of vocal pitch, twenty-first-century males differ little from our ape ancestors. In a test of nearly two hundred male college students, Puts showed that men adopted a lower pitch when speaking to males whom they perceived to be inferior to them socially and physically. In turn, those “inferior” men (who actually rated themselves as less dominant than their deeper-voiced peers) raised their vocal pitch, deferentially, when speaking to guys they saw as higher on the social and physical hierarchy.11 In the same study, the dominant, lower-voiced men reported a greater number of sexual encounters in the previous year than the men with slightly higher voices. Like our hominid ancestors, then, baritone-voiced males, it seems, get more sex—but not only because they “drive off,” or vanquish, their higher-pitched male rivals in a modern-day “contest competition” for mates. It’s also a matter of female taste.
In controlled studies, women consistently rate men with lower voices as more sexually attractive than men with higher voices.12 Puts explains this by invoking the other Darwinian mechanism by which animals choose sexual partners: “mate selection,” the notion that certain secondary sexual characteristics—like a tall, muscular, symmetrical body (suggestive of strength and health)—indicate the superior genes you’d want to pass to your offspring. Indeed, research shows that deep male voices correlate with high testosterone levels (makes sense: the more androgens, the bigger and thicker the vocal cords)—and testosterone strengthens immune response. Thus, females, in selecting deeper-voiced guys, are simply obeying an imperative wired into their brains by evolution: they choose the reproductive partner most likely to give their children the genetic advantage of greater disease resistance. But a fascinating complication emerged from Puts’s research—and one that should cheer up the high-talking Dans of this world.
Female college students have a different reaction to male vocal pitch depending on where the women are in their menstrual cycle.13 When ovulating, and thus at greatest risk for getting pregnant (and at their most libidinous), they prefer low-pitched male voices; during the least fertile part of their cycle (that is, right after their period, when they’re feeling less erotically minded), the same women prefer men with voices a few semitones higher. The deeper-voiced males were, it turned out, attractive as short-term hookups, or imaginary partners (during ovulation, the women reported fantasizing more freely about sex outside their monogamous relationships), whereas the higher-voiced guys were attractive as actual long-term mates. Apparently, women have evolved an understanding that men with deeper voices also display an array of less desirable traits typical of excessive masculinization through overexposure to testosterone: specifically, the kind of high sex drive likely to make them seek other sexual partners.14 Hence the female preference (at least, when they’re not ovulating), for men whose slightly higher voice indicates a more settled, more monogamous temperament. A guy, in short, who will stick around to help raise their offspring.
These findings are consistent with research that shows women prefer men who are less overtly masculine in all ways, not just voice. (In tests, women consistently rate as most attractive leanly muscled men over bulked-up body builders; men who are tall but not too tall; men with smooth-shaven faces over bushy beards; and men with a facial bone structure that lies more on the feminine end of the spectrum—Johnny Depp, say, over Josh Brolin).15 According to Richard O. Prum, a leading evolutionary biologist at Yale University, female mate choice is a primary force that shapes animal species, including our own: while male-on-male contest competition tends to weaponize aspects of the male body and temperament, mate selection (as determined by female choice) tends to de-weaponize it, for the understandable reason that the male special weapons (fangs, leg spurs, antlers, and deep, intimidating voices) that evolved for contest competition can also be used as tools for sexual coercion of females. By choosing reproductive partners who are less domineering (and dangerous), females produce male offspring with less coercive weaponry.16 Hence the shrinking, in Homo sapiens, of the massive incisor fangs that male chimps use both to drive off reproductive rivals and to force sex on females in acts that, to us, look distressingly like rape. This is likely how our species has ended up with male voices significantly lower than that of females, but nowhere near the rumbling growl of gorillas. With their evolved attraction to voices that are low (but not too low), women have dialed-up the average pitch of the male voice from that of our primate ancestors, even at the cost of a slightly weaker immune system in their offspring.
Darwin cited gibbons as a living example of how certain ape species use vocal melodies, in a complex duet, for courtship. If gibbons are any guide, the melodic elasticity of the voice is a big romantic draw—especially its ab
ility to soar into the upper registers, in clear high notes that (in males) indicate that the vocalizer is not only a fierce warrior, but also a sensitive, nurturing, romantic soul.
The castrati craze of the seventeenth century suggests that a high, yet still recognizably male, voice has a certain appeal to the human aesthetic sense—and perhaps especially to females in their childbearing years. Here, I would point to the enduring trend in modern pop music for extremely high male singing voices. The prepubertal Justin Bieber offers a current example, but a high, bell-pure vocal tone was also a major feature of Paul McCartney’s singing voice during the Beatlemania years, a sound that drove female audiences into paroxysms of “answering” screams. Elvis Presley, a few years earlier, provoked an identical reaction in girls with his similarly high, clear, grit-free voice on songs like “That’s All Right Mama.” Singers of a still earlier generation, Bing Crosby and Frank Sinatra (male pop singers who, with the advent of radio in the 1930s, were the first to trigger mass hysteria in teen girls), were not especially known for hitting stratospheric high notes, but their crooner-style did take down the voice’s volume, stressing the nuzzling n and m sounds, and thus making it a signal not of threat or dominance, but of intimacy, a lilting, aural caress, a thing of love, not war.
The evolutionary psychologist Geoffrey Miller draws an explicit connection between male music making and sexual success, pointing out that the singer-guitarist Jimi Hendrix had “sexual liaisons with hundreds of groupies, maintained parallel long-term relationships with at least two women, and fathered at least three children in the U.S., Germany, and Sweden.” Hendrix was, Miller says, a living example of Darwin’s theory that “sexual ornaments” (in this case the ability to make gorgeous music), greatly enhance an organism’s ability to spread its DNA into subsequent generations: “Hendrix’s genes for musical talent probably doubled their frequency in a single generation, through the power of attracting opposite-sex admirers.”17 Daniel Levitin, in This Is Your Brain on Music, makes the same argument, using Led Zeppelin singer Robert Plant as his example. Levitin quotes Plant speaking about the band’s famously (or infamously) hedonistic concert tours of the 1970s. “Whatever road I took,” Plant once said, “the car was heading for one of the greatest sexual encounters I’ve ever had.”18 The band’s appetite for groupies is, indeed, legendary. But it is worth noting here that Plant’s voice, in its glass-shatteringly high pitch and ear-crushing lung power, seems to have possessed many of the qualities that eighteenth-century critics praised in the castrati. So, ironically, Plant’s sexual success might have derived from the message his singing voice (like Bieber’s and McCartney’s) sent to female fans of a lack of sexual threat, or at the very least the promise of monogamous devotion—a dishonest signal, if ever there was one. Jimi Hendrix, meanwhile, sang in a far lower pitch, and darker timbre, than Plant or, indeed, most male rock stars. But with his Stratocaster, he made abundant use of the high notes: he let his guitar solos, with which he mimicked the sound of a keening human voice, do the wooing.
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Unlike in most bird species, where males do all the sexual singing, vocal wooing in humans is a two-way street, and the power of women’s voices to charm and seduce has been recognized since (at least) ancient Greece. Homer’s hero, Odysseus, avoided the fatal lure of the Sirens’ song only by lashing himself to his ship’s mast, his crew stopping up their ears with beeswax. (Odysseus refused earplugs because he was determined to hear what no other man had heard—and survived: the sound of the Sirens’ voices.) Homer did not describe what the Sirens actually sounded like, beyond vague allusions to their “celestial” tones, but if modern science is any guide, their voices were somewhat high-pitched and slightly breathy.
That, at least, is what laboratory tests tell us about the voices that college-aged males consistently rate as the most sexually attractive in females.19 Evolutionary biologists believe that men developed a preference for a relatively higher female pitch because it carries a message of youth and thus reproductive health (women’s voices deepen with age and the onset of menopause).20 Breathiness, meanwhile, is a positive sexual signal because it derives from a tiny anatomical difference between the male and female larynx that emerges at puberty: women’s vocal cords do not close, completely, at the back of the larynx, when phonating. The minuscule gap between the membranes allows a small amount of air to escape “unchopped,” lending a whispery edge to women’s speech.21 Thus men, in their search for the most feminized (and thus most fertile) partner, are subconsciously attracted to women with a higher pitch and some telltale purring turbulence in their vowels and voiced consonants. This would help to explain the popularity of the actress Marilyn Monroe, who deliberately exaggerated all aspects of human sexual dimorphism, with her spiked high heels, curvy walk, hydraulic brassieres, cinched-in waist, heavy makeup—and high-pitched, whispery, kewpie-doll voice; a voice that, in sexual-selection terms, advertised “youthful” fertility to the point of parody.
As Monroe’s vocal exaggerations suggest, the sexual dimorphism of the human voice is not purely a result of anatomy. Social expectations, cultural pressures, gender norms, and individual psychology all affect how men and women tune their vocal pitch and voice quality. A 1995 study by a Dutch research team showed that Japanese women speak several semitones higher than women in Western countries, and at a softer volume: a voice consistent with the traditionally approved role of women in Japanese society, where a code of female conduct, called onnarashii, rewards “modesty, innocence, dependence, subservience.”22 Japanese men reinforce this socially imposed divide by speaking at a pitch a few semitones lower than men in the West. North American and European men also drop their voices into an artificially low pitch to advertise their maleness, but usually when in same-sex groups, like sports bars and locker rooms, where they can be heard booming at each other in passive-aggressive displays of “camaraderie.” This super-masculinized voice is especially off-putting when speakers transport it from all-male enclaves and use it in their personal or professional lives.
Experimental psychologist Nalina Ambady showed just how off-putting. She used a device called a low-pass filter on recordings of surgeons speaking to patients in routine office visits. The filter removes all language content from speech, but preserves tone and pitch—the prosody. Listener-judges were asked to rate the voices for “warmth,” “anxiety,” “concern,” “interest,” “hostility,” and “dominance.” Using only those ratings—and with no knowledge of the doctors’ professional histories or competence—Ambady was able to predict, with 100 percent accuracy, which surgeons had been sued and which had not.23 A dominant tone (“deep, loud, moderately fast, unaccented, and clearly articulated”) was the giveaway for who got sued. The listener-judges reported that these voices conveyed “lack of empathy and understanding.” Surgeons with “warm,” “sympathetic,” or “concerned” voices faced no malpractice claims—even when they had histories of harming patients through incompetence or negligence. The off-putting voices that triggered vengeful lawsuits were defined largely by their excessive baritone pitch.
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Women have hardly been deaf to the message of power that a lower voice bestows on the speaker and they have, for some time now, been adjusting their voices downward. Speech pathologists in Australia recently compared the voices of young adult women recorded in 1945 with the voices of Australian women recorded, under identical conditions, in 1993.24 The team discovered that in the intervening fifty years women’s pitch had dropped, on average, almost two semitones—a significant change. Studies of American, Canadian, and Swedish women showed that they speak in the same lowered range as Australian women. Furthermore, earlier studies (from the 1920s and 1930s) reveal that women once spoke at a still higher pitch than that of women in the 1940s—as high as 318 cycles per second, more than half an octave higher than women today.
The steady drop in female vocal pitch parallels, and was almost certainly driven by, the seismic changes in women’s s
ocial status over the last century, beginning with the international suffrage movement, which by 1920 had earned women the right to vote in countries throughout the West. Female vocal pitch continued to drop during the Second World War, when women were liberated from the roles of housewife and mother and called on to fill positions of authority in the workplace vacated by men who had gone to fight. Women were also recruited as reporters and announcers on radio, where they were obliged to speak in a lower pitch than normal because of audio equipment designed for broadcasting men’s voices (speech in higher registers tended to distort).25 C. E. Linke, a voice specialist at Tulane University, says that the “psychosocial influence” of popular women radio personalities during the war helped to drive down the fundamental frequency of female voices across society.26
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