Why Is the Penis Shaped Like That?: And Other Reflections on Being Human
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So in my plumbing of the empirical literature for studies on unprotected anal sex among gay males, otherwise known as “barebacking,” I came across a load of research on this very topic. Most of this work is couched, understandably so, in the HIV-prevention literature. One particularly telling study, though, comes from a 2005 report from the journal Nursing Inquiry in which the Canadian investigators Dave Holmes and Dan Warner interviewed barebacking gay males—not while they were engaged in the act, but through later introspection—about their motivations for preferring unprotected anal sex over condoms in light of the obvious dangers of infection. The most intriguing result to emerge from this study, in the context of Gallup and Burch’s overall theoretical perspective regarding the psychobiology of semen, was that so many of the barebacking interview subjects viewed the exchange of semen through unprotected anal sex as providing them with a palpable sense of “connectedness” with their same-sex partners, one that happened only with the internally unimpeded ejaculation.
Unfortunately, rather than investigate the possible psychobiological effects of semen exchange in this dynamic, Holmes and Warner leer through a fairly typical postmodernist lens to explore the symbolic nature of semen exchange in barebackers. Now, I ask you, which is the more informative paradigm for understanding why gay men would practice unsafe sex through unprotected anal intercourse: an evolutionary biological account taking into consideration the chemical composition of seminal plasma and its possible effects on attachment among gay men, or a symbolic, postmodernist perspective like the following one advanced by Holmes and Warner (in all fairness, this is just a snippet, but a good taste of their approach)?
The body becomes the locus of never-ending fights, a carnal battlefield. The escape route (lines of flight) is intrinsic to the deterritorialization of the Body-without-Organs through which one becomes someone else. However, the lines of flight could have paradoxical effects. Indeed, they can be avenues of creative potential or, conversely, paths of great danger. Yet, it is “always in a line of flight that we create” … “that we must continue to experiment with such lines.” Lines of flight (nuclei of resistance of resingularization and heterogenesis) permit freedom to surge through a process of creative transformation and metamorphosis.
Trust me, even in context, that reads as if the authors were cobbling together a Braille sentence using the random distribution of acne on someone’s back. Sorry to sound a bit testes—er, testy—but while such soupy postmodernist rhetoric may still have its place in certain scholarly circles, when one is dealing with something as clinically important as unprotected sex among vulnerable populations, a scientific understanding of these people’s motivations is essential before any intervention of their high-risk behaviors can even begin to occur.
You may also be beginning to realize the dangers that I alluded to at the start of this essay. For both men and women, heterosexual and homosexual, knowing that the penis is capable of dispensing a sort of natural Prozac—whether obtained vaginally, anally, or orally—without also considering the viral arms race involving sexually transmitted infections can lead to very tragic decisions indeed and many undocumented high-risk, private bedroom semen “experiments.” But here’s just one reason to put the brakes on such plans: the HIV virus, which evolved long after these adaptive antidepressant factors, has apparently come to pirate human semen, such that certain protein factors in seminal plasma, particularly a protein called prostatic acid phosphatase, make HIV up to 100,000-fold more potent than it is outside of the plasma.
In any event, Gallup and Burch’s model also reminded me of those oft-cited Papua New Guinea tribes, such as the Sambia, and their semen-ingestion rituals involving young boys. On the surface, there’s a puzzling scenario here: such cultures have long histories of being embroiled in violent warfare, and thus they tend to place extraordinarily high value on expressed masculinity. Yet ritualized homoerotic practices involving young boys fellating older males in order to ingest their semen are common. In an issue of the Archives of Sexual Behavior, Gilbert Herdt, a cultural anthropologist who studied the Sambia, along with his colleague Martha McClintock (the same McClintock after whom the menstrual cycle synchrony effect discussed earlier was named), describes how “by the age of 11–12 [Sambia] boys have become aggressive fellators who actively pursue semen to masculinize their bodies.”
In the past, cultural anthropologists such as Herdt have conceptualized this semen ritual mostly in symbolic terms. Yet since testosterone from the seminal plasma could penetrate the oral mucosa, along with a surfeit of other hormones and chemicals having possible spin-off effects on male behavior, I do not find it inconceivable that there may be genuine psychobiological consequences of semen intake occurring in these young swallowing males that are not wholly out of line with the Sambia’s own folk beliefs. It might not be a theory you want to run by your local pastor or bring up at your next PTA meeting, but you get the idea.
But let’s get back to more everyday semen ingestion. (Maybe not every day, but you know what I mean.) In addition to their semen-as-antidepressant model, Gallup and Burch have worked out many other intricate, persuasive arguments about how the various chemicals in human semen served—and continue to serve—biologically adaptive functions for both sexes. For example, among the more curious ingredients in human semen are follicle-stimulating hormone (FSH) and luteinizing hormone (LH). This is curious, Gallup and Burch point out, because these are distinctively female hormones. What are female hormones doing in human semen? The authors speculate that the presence of FSH and LH in human semen is related to concealed ovulation in human females.
Unlike females of other primate species, women do not have breeding patterns governed by season or standardized cycles, and there are no obvious signals—such as a fire-engine-red swollen rear end—giving away their time of the month. So for a naive human male, impregnating a woman as a consequence of sexual intercourse is much more a roll of the dice than it is for males of other species in their mating behaviors. Just as with any other species, though, getting the timing right so that release of semen coincides with the release of eggs is key. As a counterdefense against women’s concealed ovulation, male evolution had a trick up its sleeve, which was the ability to manipulate the timing of a woman’s ovulation to suit a man’s own insemination schedule; that is to say, semen chemistry gives premature eggs a nice little nudging. Hence the conspicuous presence of FSH (which causes an egg in the ovary to ripen and mature) and LH (which triggers ovulation and release of that egg).
In support of this theoretical claim about semen chemistry and concealed ovulation in human females, consider that chimpanzee semen lacks the FSH hormone altogether and the presence of LH is rather negligible, which makes sense, of course, since chimpanzees are cyclical breeders and ovulating females display their own personal red-light-district signs by way of swollen, multicolored anogenital regions. “Thus it would appear,” reason Gallup and Burch, “that the chemistry of human semen has been selected to mimic the hormonal conditions that control ovulation, and as such may account for instances of induced ovulation (ovulation triggered by copulation at points in the menstrual cycle when ovulation would otherwise be unlikely).”
Believe it or not, we’ve only scratched the surface of the evolved-semen literature. Here’s a snapshot of other recent findings from Gallup’s lab, most, remember, needing further investigation before we jump to any strong conclusions: semen-exposed women perform better on concentration and cognitive tasks; women’s bodies can detect “foreign” semen that differs from their long-term or recurrent sexual partner’s signature semen (an evolved system that, Gallup believes, often leads to unsuccessful pregnancies—via greater risk of preeclampsia—because it signals a disinvested male partner who is not as likely to provide for the offspring); women who had unprotected sex with their partners—and therefore were getting regularly inseminated by them—experience more significant depression on breaking up with these men than those who were not as regula
rly exposed to an ex’s semen (and they also go on the rebound faster in seeking new sexual partners, which presumably would help fix their semen-deprived depression). And the list goes on.
Before I bid adieu, please accept, ladies, in all sincerity, my humblest apologies for what is likely to be a flood of inappropriate remarks from men saying, “I’m not a medical doctor, but my testicles are licensed pharmaceutical suppliers.” I’m just the merry messenger.
PART II
Bountiful Bodies
The Hair Down There: What Human Pubic Hair Has in Common with Gorilla Fur
Like many people, I ask myself continuously about some of life’s biggest mysteries. Why are we here? What is the meaning of life? Why do we have those strangely sparse, wiry little hairs growing around our genitals—hair that is singularly different from all the other hair on our bodies? Fortunately, scientists have managed to put my mind at rest on at least one of these daunting existential questions. In recent years, it seems, researchers have made some tremendous advances in the study of pubic hair.
So, let’s start with what we already know about pubic hair. It’s a signature of sexual maturity, sprouting up around our groins sometime in early adolescence. If it appears on a person’s body any time earlier than this in development (say, prior to the age of nine years old), something is clearly the matter. Some things just don’t go together in this world—babies and pubic hair are definitely two of them.
Precocious puberty is no laughing matter, of course, because children who begin to develop secondary sexual characteristics unusually early in their development may in fact have some significant underlying health problem, such as a lesion on the central nervous system that prematurely activates the hypothalamus. But for one young couple in Alabama, the term “precocious puberty” hardly does justice to what they were observing with their infant son a few years ago. Just imagine changing your six-month-old’s diapers and noticing what appears to be a tuft of light-colored pubic hair on his groin. Over the next ten months, the pubic hair would become progressively darker and adultlike, which—when accompanied by an oddly large penis for a sixteen-month-old and, ahem, frequent erections—was finally enough to prompt this pair to seek medical advice.
This was the background of the case as it was presented to a group of physicians that eventually reported it in Clinical Pediatrics. Upon examining the child, Samar Bhowmick and his colleagues noted with some astonishment that “the pubic hair was [that of an adolescent], mostly around the base of the phallus and was dark and curled.” Further inspection revealed a healthy, bouncing baby boy—completely age appropriate in all other respects—but the laboratory results indicated an abnormally high level of testosterone. Eventually, the doctors cracked the case. It turned out that the boy’s father had been spreading testosterone gel twice daily over his shoulders, back, and chest, having been prescribed this treatment by his doctor to treat a low libido brought on by depression. Because the little boy slept in the same bed as his parents, with his father cuddling and hugging his child just after applying the gel, the bare-skin contact was causing his son to become a man much earlier than nature intended. (A follow-up visit later revealed, fortunately, that the pubic hair had all but disappeared once the father was made aware of this effect of his gel use, and the doctors were hopeful that the child would have no long-term complications from the testosterone exposure.)
This peculiar case of the pubic-haired infant is so striking, obviously, because this type of distinctive groin pelage tends to coincide with sexual maturation, not the developmental stage in which we’re just learning how to walk. The case also highlights the oddity that is human pubic hair more generally. After all, we appear to be the only species of primate (perhaps the only species, period) that bears this type of strange hair around our genitals. Robin Weiss, a researcher from University College London’s Division of Infection and Immunity, found himself standing in the shower one day, looking down, and asking this very question:
Although naked apes [humans] have pubic hair, surely our hairy cousins don’t? How could I test my hypothesis? I knew that there was a stuffed chimpanzee in the Grant Zoological Museum at University College London and I called in on the way to my laboratory. Alas, he was a juvenile, which left the question open. A brisk walk across Regent’s Park to inspect the adult gorillas in their splendid new pavilion at London Zoo strengthened my suspicion, and this was later confirmed by a visit to the chimpanzees at Whipsnade Zoo north of London. Indeed, all the species of apes, Old World monkeys and New World monkeys seem to be less hairy in the pubic region than elsewhere; fur is present but it is short and fine.
Weiss speculates that one of the main reasons that human beings uniquely evolved a “thick bush of wiry hair” around their genital regions is to visually signal sexual maturation. (It also likely serves as a primitive odor trap and aids in the wafting of human pheromones.) So pubic hair acts as a furry advertisement, indicating for prospective sexual partners that mating with that individual could potentially be a fruitful exercise in genetic perpetuity. Weiss believes that showing off our fecundity this way suggests pubic hair would have arisen only after we became “naked apes,” causing it to stand out so vividly against the backdrop of an otherwise hairless body.
Another fascinating thing about pubic hair is its unusual texture and composition compared with the rest of the hair on our bodies and heads. You can’t quite use it to floss with (trust me), but pubic hair is considerably thicker than either axillary (underarm) hair or that on our legs, chests (for some, backs), and scalps. I’m probably not the only one who shudders to think of an alternative path of natural selection, one in which the hair on our heads evolved to be of pubic proportions—just consider what the average barbershop floor might look like at the end of the day. It’s not entirely clear why pubic hair is so distinctly thick, short, and, usually, curly, but the biologist Anne Clark from SUNY Binghamton did point out to me (while we were hiking on the feathery and furless Kapiti Island in New Zealand, which made it all the more memorable) that anything else would be rather impractical. To have long, flowing, stylish locks growing down there wouldn’t be terribly convenient, especially given the logistics of sexual intercourse.
But, as Weiss points out, although pubic hair had its signaling advantages, it also came with a cost. And this cost goes by the name of Phthirus pubis—more commonly known as crabs. The evolutionary story of crabs is remarkable, and it’s one that Weiss relays in an issue of the Journal of Biology. If you’ve ever marveled at the similarity between human pubic hair and the coarse texture of gorilla hair (and let’s face it, who hasn’t), you’re already on the right track:
On the basis of morphology, human Phthirus pubis is closely related to the gorilla louse, Phthirus gorillae … Molecular phylogeny indicates that human pubic lice diverged from gorilla lice as recently as 3.3 million years ago, whereas the chimp and human host lineage split from the gorilla lineage at least 7 million years ago. Thus, it seems clear that humans acquired pubic lice horizontally, possibly at the time of the Phthirus species’ split and probably directly from gorillas. Because they were already adapted to the coarse body hair of the gorilla, crabs would have found a suitable niche in human pubic hair.
That’s right. We got crabs from gorillas. But get your head out of the jungle gutter. Weiss speculates that our ancestors acquired these ravenous parasites not through interspecies sex but as a consequence of ancient humans butchering and eating gorillas. This close contact with gorilla carcasses would have enabled the gorilla louse (Phthirus gorillae) to jump hosts and mutate in accordance with the eventual evolution of human pubic hair—what must have seemed a cozy and familiar environment—to become the Phthirus pubis species we know and loathe today (much as bush-meat slaughter practices allowed retroviruses to invade humans from chimpanzees more recently).
Regardless of how they came to be there, crabs have unfortunately become part and parcel of our species’ pubis. Intriguingly, however, recent behavior
al innovations in our species’ cultural evolution—particularly, modern grooming habits and the aesthetic stylizing of our pubic hair regions—have begun prying loose these pesky critters’ grip on us. Some health clinics have noted a significant fall in the occurrence of pubic lice, especially among patients who shave all or some of their pubic hair. (And even if only their sexual partners shave down there, the risk of acquisition in the patients themselves should still be substantially less than for those who mate with partners whose genitals are hidden in the type of thick copse that crabs delight in.) This isn’t an entirely new phenomenon. Prostitutes in medieval times would often wear “merkins” (or pubic wigs) after shaving their genitalia to help control their pubic lice.
But before you go scheduling your next full Brazilian wax, consider that pubic hair does appear to offer some degree of protection against even nastier bacterial and viral infections. Although the diagnosis of pubic lice has seemingly plummeted as a direct result of human vanity in both sexes, cases of gonorrhea and chlamydia have increased over the same period, a correlation that may not be merely coincidental. Damned if you do shave, damned if you don’t.
Still, the “hairlessness norm” is gathering a lot of steam, particularly in Western countries. Several recent studies reveal just how common shaving one’s nether regions has actually become. In an issue of Sex Roles, the Flinders University psychologists Marika Tiggemann and Suzanna Hodgson found that 76 percent of a sample of 235 female undergraduates from Australia reported having removed their pubic hair at some point in their lives. Sixty-one percent currently did so, and half of this sample said that they routinely removed all traces of their pubic hair. The current trend for men appears to be no different. In a separate study the same year, with her colleagues Yolanda Martins and Libby Churchett, Tiggemann reported in Body Image that of 106 gay men, 82 percent had removed their pubic hair at least once. And lest you think that this is an artifact of gay male culture, straight men weren’t far behind on this measure. Out of a sample of 228 heterosexual men, 66 percent reported doing the same. Irrespective of sexual orientation or gender, the investigators discovered that the primary motivation for pubic hair depilation is related to concerns with one’s appearance (in contrast to health-related motivations).