How Sex Works
Page 15
“Same-sex sexuality is just another way of maintaining physical intimacy,” says Roughgarden. “It’s like grooming, except we have lots of pleasure neurons in our genitals. When animals exhibit homosexual behavior, they are just using their genitals for a socially significant purpose.”
Some of this thinking about same-sex sexual contact in animals shares common ground with theories about the evolutionary purpose behind female orgasm. That is, they both suggest that sex has a role facilitating bonding and positive social cohesion that goes beyond reproduction.
So if all this homosexual behavior is rampant among animals, why isn’t it more widely known? “Although the first reports of homosexual behavior among primates were published more than 75 years ago, virtually every major introductory text in primatology fails to even mention its existence,” says primatologist Paul Vasey. It may very well be that politics and personal predispositions have gotten in the way of reporting these behaviors. As biologist Valerius Geist admitted more than two decades ago, “I still cringe at the memory of seeing old D-ram mount S-ram repeatedly. To conceive of those magnificent beasts as ‘queers.’ Oh God!…Eventually I called the spade a spade and admitted that the rams lived in essentially a homosexual society.”
WHEN IT COMES to humans, of course, the great debate over sexual orientation is one of origin. Nature—predetermined by genes or other biological factors? Or nurture—the product of an individual’s environment and its subsequent influences? A combination of both—or simply a choice? Few in the scientific community believe it to be purely a choice or purely biological. The scientific literature abounds with significant correlations between possible biological factors and sexual orientation of individuals—but it’s also filled with examples of people whose orientation contradicts those expectations. Remember, correlation means researchers have identified a pattern indicating that one or more traits tend to be associated; it does not mean that those traits can influence one another.
One of the most prominent—and controversial—studies to suggest a biological correlation to homosexuality is a study of male twins authored by two psychologists, Michael Bailey of Northwestern University and Richard Pillard of Boston University. According to their study, if a male identical twin was gay, the odds of his brother being gay were around 50 percent—as much as ten to twenty times more likely than someone in the general population. Even in pairs of male fraternal twins, where siblings only share about half their genes with each other, the psychologists found that if one brother was gay, the odds of the other brother being gay were about 20 percent. Of course, just as this study suggests a biological correlation, it also seems to rule out genetics as the only factor in determining orientation.
These studies aren’t the only ones that suggest a biological source for sexual orientation; there have been many others, like the scent studies discussed earlier, showing how the brains of homosexual men process male scents the same way that heterosexual women do, and the brains of lesbian women process female scents more like heterosexual men.
Many of these studies are underfunded. This means they are often relatively small, which, in turn, makes them less conclusive. The smaller a study is, usually the less statistically certain its results. But many scientists believe that, taken together, all these studies form a composite picture that looks a lot like a biological signpost, albeit a small one. The research “all sort of pointing in the same direction makes it pretty clear there are biological processes significantly influencing sexual orientation,” says neuroscientist and author Simon LeVay. “But it’s also kind of frustrating that it’s still a bunch of hints, that nothing is really as crystal clear as you would like.”
If these researchers are right, and there is a biological link to homosexuality, besides assisting with social cohesion, how did it survive in the gene pool? In other words, if there’s a gay gene or genes that predispose an individual to nonreproductive homosexual behaviors, how does that gene continue to get passed on instead of dying out?
An Italian study offers an intriguing possibility: What if a genetic combination that makes a woman more fertile, or fecund as researchers call it, also works to incline a man toward homosexuality? Professor Andrea Camperio-Ciani and a team of researchers at the University of Padua interviewed ninety-eight gay and one hundred straight men, getting detailed family histories from them covering some 4,600 relatives. And they found that the female relatives of gay men, mothers and maternal side aunts, produced significantly more children than the mothers and maternal side aunts of straight men. That the difference was found only on the maternal side suggests that the genetic link, if there is one, may be found on the X chromosome, which males only receive from their mothers. Dr. Camperio-Ciani’s latest 2008 study found the same correlation in the families of bisexual men—their female relatives had more children. Again, it’s important to note that just because the researchers found a correlation in these studies, it doesn’t actually mean they found a genetic connection.
Still, Dr. Camperio-Ciani is downright bullish about his work, feeling that it sheds light on the evolutionary mystery of homosexuality: “We have finally solved this paradox,” says Camperio-Ciani. “The same factor that influences sexual orientation in males promotes higher fecundity in females.”
The possibility certainly merits further investigation and has a logical appeal from an evolutionary perspective. It’s a lot easier to imagine the long-term survival of a gene promoting female reproduction that sometimes gets in the way of male reproduction than it is to imagine one that simply acts against male reproduction all the time. Commenting on the first Italian study, Dr. LeVay said: “We think of it as genes for ‘male homosexuality,’ but it might really be genes for sexual attraction to men. These could predispose men towards homosexuality and women towards ‘hyper-heterosexuality,’ causing women to have more sex with men and thus have more offspring.”
“It helps to answer a perplexing question—how can there be ‘gay genes’ given that gay sex doesn’t lead to procreation?” says Dean Hamer of the National Institutes of Health. “The answer is remarkably simple: the same gene that causes men to like men also causes women to like men, and as a result to have more children.”
Even if it’s right on the mark, the Italian study only tells a part of the story. Dr. Camperio-Ciani estimates that the effect his report describes accounts for less than a seventh of male homosexuals: “Our findings are only one piece in a much larger puzzle on the nature of human sexuality.” Nevertheless, it’s intriguing—evolution selecting for a gene that encourages women to have more children, even if some of them will be males with some inclination toward an orientation that takes them out of the reproductive pool.
As our understanding of just how genes work has deepened, scientists have started looking for clues to that larger puzzle beyond just gay genes. “Genetics is not determining the sexual orientation, it’s only influencing it,” says Camperio-Ciani. And recently, the search for a biological component to sexual orientation has focused on the influence of a baby’s fetal environment—that is, the womb—on its genes and development. For most of its history, the field of genetics has believed that genes were somewhat immutable blueprints, directing your body to build itself according to set plans. In the last few years, though, our understanding of the interaction between genes and the environment has completely changed. We now know that certain genes can actually be turned on or off, much like flicking a light switch. One of the ways that this can occur is through a chemical process called methylation. All kinds of things can have an influence on this process, from cigarettes, to diets low in critical nutrients, as well as diets rich in others. And the process is clearly at work during pregnancy—the environment a mother lives in, her diet, even her anxiety can turn specific genes on or off in her developing fetus. Certainly this process could have an effect on genes that influence sexuality, as various factors influence the genes turning on or off.
As discussed in Chapter 5, one of the
ways the expression of a given genetic sequence can be implemented or suppressed is through hormones and the body’s receptivity to them. Women with androgen insensitivity syndrome, for example, have the genetic code to be men—they are XY—but, because they lack the hormonal receptors necessary to respond, they don’t react to the testosterone that would otherwise trigger masculinization in the womb, and they follow a largely female developmental path. So although they are genetic males, the majority of women with AIS (XY), like genetic females (XX), are generally thought to have heterosexual preferences, and are thus attracted to men.
University of Oklahoma urologist Dr. William Reiner has examined more than a hundred cases in which genetic males—XY—were born with very underdeveloped or missing penises, subjected to surgical castration and genital “reconstruction” as females, and raised as girls. “I haven’t found one who is sexually attracted to males,” says Reiner.
This leads some researchers to believe that sexual identity and maybe sexual orientation are established in the womb before the genitals are even formed, as the brain is washed in waves of sex hormones. Reiner elaborates, “Exposure to male hormones in utero dramatically raises the chances of being sexually attracted to females. We can infer that the absence of male hormone exposure may have something to do with attraction to males.”
More evidence that prenatal hormone exposure has some connection to sexual orientation is in your hands. Literally. Generally speaking, men have index fingers that are slightly shorter than their ring fingers. For women, the two fingers are usually closer in length. Scientists from the University of California at Berkeley have shown that the fingers of lesbian women follow the same pattern as men, with shorter index fingers. They think this may be the result of exposure to higher than normal levels of androgens, male sex hormones, during fetal development.
Seems like it’s starting to make sense, right? Genetic men (XY) who don’t respond to testosterone develop physically as females and are attracted to men. Females who are exposed to high levels of male hormones have male-pattern fingers and are attracted to other females. Not all men who are exposed to especially high levels of male hormones have especially male-pattern finger lengths, which follows the pattern—but they also tend to be attracted to other men, which doesn’t.
That’s right, some researchers think that men who are exposed to especially high levels of male hormones tend to be attracted to other men. It’s actually not quite that simple—but it’s more evidence that the chemical stew that influences sexual orientation, if it does, involves a pretty complex set of ingredients. The same study of finger length showed that gay men with several older brothers tended to have much shorter than normal index fingers relative to their ring fingers—in other words, the same phenomenon that masculinized the fingers of lesbians seemed to be at work but only if they had two or more older brothers. What’s particularly interesting about this correlation is that previous research has shown that having several older brothers actually increases the odds that the subsequent child will be gay. The researchers believe that somehow there is an increase in the amount of androgens a mother’s subsequent baby is exposed to, resulting in the “extreme” male finger patterns, and perhaps influencing orientation as well. Androgens, remember, are the hormones that can trigger male development. How exactly that happens, of course, is still very unclear.
But the one thing almost everyone agrees on is that sexual reproduction is incredibly complicated and there are numerous ways for things to turn out—from differentiation in the genitals, the rest of the body, or the brain; in the chemistry of identity, attraction, and desire; and, of course, in the complicated biological merger of genes from two parents, starting the whole miraculous process over again.
Which brings us full circle again—why sex?
CHAPTER 7
tainted love
In 1995, when I was a college student, I spent the summer working at an orphanage in Bangkok, Thailand, called Tarn Nam Jai. It was an HIV/AIDS orphanage. All of the children there had lost their mothers to the epidemic that has ravaged so much of Africa and Asia. And the orphanage wasn’t just an orphanage; it was a hospice too. About a quarter of children born to HIV-positive mothers become infected with the virus themselves. So Tarn Nam Jai had a double challenge—caring for the children with HIV and finding homes for the children who weren’t infected. Of course, the very fact that Tarn Nam Jai had two missions was a miracle in itself. How did three-quarters of the children, all born to women with HIV, escape infection?
The placenta-uterus interface is an extraordinary viral filter, and normally about three-quarters of the time is able to prevent the HIV virus—an especially insidious string of “genetic code”—from passing from mother to child. The fact that pregnancy can prevent HIV from infecting a fetus is a powerful testament to its effectiveness, but that’s just a part of the story. HIV is so insidious because of the way it replicates itself, or reproduces. It’s a retrovirus; it uses an enzyme called reverse transcriptase to actually write itself into the DNA of the person it has infected, becoming a permanent part of his or her genetic code. So every time a person’s infected cell reproduces, HIV reproduces along with it. Unlike sexual reproduction (which requires a male and a female), asexual reproduction occurs when an organism makes an exact copy of itself. If a human infected with HIV reproduced this way, it would copy HIV right along into its offspring. Every time.
Sexual reproduction essentially helps us to wipe the biological slate clean; it helps to prevent us from passing along whatever infections we may have acquired in our lives. And that’s not all. Sexual reproduction allows for genetic reassortment, almost like shuffling a deck of cards but on the genetic level. Every time we shuffle the deck, there’s some chance of a new combination, one that may produce a stronger trait in our offspring, like an immune system that can outwit a new virus or bacterium. Asexual reproduction doesn’t usually allow for a reshuffling of the genetic cards, but more or less ensures that an organism’s offspring will be no better off than its parent.
Sex gives the species two big advantages in the evolutionary sweepstakes: it can at times protect children from the responsibility for their parents’ biological mistakes. It gives those children the chance to biologically outdo their parents. That’s why sexual reproduction may be pretty rampant throughout nature. Unfortunately, it also allows a mother to harm her child, through alcohol and/or drug abuse, before the child is even born. Yes, there are all kinds of ways sex can go wrong, and yes, it comes with all kinds of costs. And yes, it’s expensive.
But you get what you pay for.
SEX HELPS US to give our children a clean bill of health, working to spare them from a lifetime’s accumulation of parasites, viruses, and other pathogens. But remember, evolution is all about trade-offs, and the world is filled with opportunistic creatures, some large and some very, very small. Another significant cost of sexual reproduction is that the very act of sex opens up a whole new niche for some of those creatures to move from one host to the next. File that under life’s little ironies: sex protects our children from inheriting infections while exposing us to the risk of more infection in the process.
And, of course, it doesn’t provide perfect protection, not by a long shot. As I said, the miracle I witnessed at Tarn Nam Jai was that three-quarters of the children escaped infection. But heartbreak was the flip side of the miracle—for every three children born healthy there was a child born dying. The face of one of them has never left me. His name was Johnny, he was five years old, and he had full-blown AIDS. His body was unbelievably frail, his belly was grossly distended, but most of all, he was in so much pain, dying shortly after I left Thailand.
Watching children die of HIV left me with a clear conviction: in order to stay one step ahead in the evolutionary arms race, nature may have led us down a path filled with perils, but that doesn’t mean we can’t defend ourselves against some of them, and sexually transmitted infections is a good place to start.
STIs have typically been associated with a stigma not attached to many other diseases, which makes it all the more important to have a clear understanding of how they’re transmitted, the risks they pose, and what their warning signs are.
The most common sexually transmitted virus in the United States is actually one that many people are unfamiliar with, although it’s gotten a fair amount of attention in recent years, not so much because of the damage it does on its own but because of the additional risks it poses for people infected with it, especially women. That virus is human papilloma virus, or HPV.
At least a quarter of American men and women have been infected with HPV. 6.2 million new infections happen every year. HPV can often infect without causing any symptoms, but in some cases it causes genital warts—warts with a cauliflower-like appearance, commonly found on the penis, vulva, and anus. Sometimes those warts can go away on their own, but if they don’t, they can be removed by a doctor, much in the way warts on the foot or hand are removed, through surgery, cauterization, or cryotherapy (freezing them off with liquid nitrogen). So far, there’s no complete cure. In severe cases HPV can cause genital warts that can be very disfiguring and quite traumatic. But it’s not HPV’s manifestation as warts that has earned it headlines recently.
HPV is the main cause of cervical cancer in women, the second leading cancer killer of women worldwide. In the United States, cervical cancer is diagnosed in about 10,000 women every year, and 3,700 die from it. HPV has also been linked to oral, rectal and anal cancers in both men and women. With the increase in prevalence of oral and anal sex amongst heterosexual couples, it’s thought that we may see a corresponding increase in HPV-related cancers.