Then came a pair of studies in Kenya and Uganda; the Kenyan study found a 53 percent lower incidence of HIV infection among circumcised men and the Ugandan study, 48 percent. The findings were so dramatic, that the National Institutes of Health, which conducted the studies, decided that ethics compelled them to halt the studies midway and offer the uncircumcised participants the opportunity to be circumcised.
More research is still needed, especially because these studies were never actually completed. Modern medical research is generally conducted by studying people receiving a treatment or procedure and comparing them to similar people who do not receive that treatment or procedure; the untreated group is called a control group. If the treatment shows significant positive results early in the study, ethics requires that researchers stop the study and offer the treatment to the untreated group as well. Of course, that also means that you can’t be sure what the studies actually would have shown if they had been carried to completion. Perhaps the apparent benefits of circumcision wouldn’t have lasted over the long run. Or worse, maybe circumcision would have been shown to increase the risk of contracting HIV. There’s no way to know without completing the study.
Now, even if circumcision helps to dramatically reduce the risk of HIV infection, it’s by no means a grant of immunity. Circumcised men can still get HIV, and they do all the time. But, combined with safer sex, there’s mounting evidence that it really may reduce the risk. Dr. Halperin overlays the prevalence of circumcision and the average number of sexual partners, in a series of African nations, in a striking analysis that bears that out. As he explains, an estimated 15 percent of men in Botswana are circumcised and 65 percent of men report sex with multiple partners; the AIDS rate there is a staggering 25 percent. But in Tanzania, although a similarly high 52 percent of men report high-risk sex, 70 percent of them are circumcised, and the AIDS rate is much lower, at 7 percent. And in Ethiopia, where 75 percent of men are circumcised and only 21 percent report sex with multiple partners, the AIDS rate is 2 percent.
Yet there has been some conflicting research. A recently published study in the African Journal of AIDS Research found that in some countries, including Cameroon, Lesotho, and Malawi, circumcision in fact appeared to increase the transmission of HIV. And certainly the act of circumcising adults increases the risk of contracting a sexually transmitted infection if the newly circumcised man engages in intercourse before his penis is completely healed.
HIV is a retrovirus that can insert itself into our cells’ DNA; this is, in part, what makes it so hard to cure once it has infected someone. HIV is particularly insidious because it targets the cells of our immune system (such as T-cells, which usually protect us from infection) and hijacks them to facilitate its own reproduction. That hijacking eventually destroys those cells, leading to the immune system breakdown we know as acquired immune deficiency syndrome, AIDS. Langerhans’ cells, which can also be infected by HIV, are a specialized type of immune cell found in the skin. And guess what part of the body is full of them? The foreskin. So by removing the foreskin you might be removing a prominent site for HIV infiltration. Or so the thinking goes.
HIV isn’t the only virus that may be impacted by circumcision. A study published in 2008 in the Journal of Infectious Disease looking at 351 men found that uncircumcised men are at increased risk for infection with the human papillomavirus (HPV), including a type of HPV that is involved in cancer of the penis and cervix. HPV is thought to be one of the most common sexually transmitted infections. The multiethnic Hawaiian study found that 46 percent of uncircumcised men had HPV in the glans or corona, whereas only 29 percent of circumcised men were infected. In an accompanying editorial commenting on the study, Dr. Peter V. Chin-Hong of the University of California, San Francisco wrote: “Evidence that male circumcision is associated with decreased penile HPV infection is rapidly accumulating.” There are some design limitations to the study, however. It’s small, and the circumcised men tended to be older and were more likely to be of Asian descent. When it comes to susceptibility and resistance to disease, genetic differences between ethnic groups can play a large role. For example, people from the eastern Mediterranean and parts of Africa are thought to have developed, through natural selection, a greater resistance to malaria than people who belong to other ethnic groups. So it’s possible that the Asians in the study may have had some genetic resistance to HPV infection, and circumcision didn’t have anything to do with it.
Another well-known fact may reveal another piece of the puzzle. Scientists have noted for years that women who had uncircumcised male sex partners were at greater risk for cervical cancer. The Hawaiian study also found that even circumcised men with high-risk behaviors for HPV infection (defined as having six or more lifetime sexual partners or sex with prostitutes) were less likely to infect their female sexual partners with HPV. This helps protect their partners from developing cervical cancer, as compared to uncircumcised men. Because of this, some people believe that Gardasil, the quadrivalent vaccine that targets four types (or strains) of HPV may also lower the rate at which men get HPV. These are types 6 and 11, associated with genital warts, and types 16 and 18, which can spawn abnormal cell growth, such as cervical cancer.
If fewer women get infected, there are fewer people who can pass it on. This begs the question: Why don’t boys and men just get vaccinated for HPV? Merck, the maker of Gardasil, is hoping to do just that by getting approval to vaccinate boys and young men. Of course, we still don’t know if there are any long-term adverse effects from Gardasil. This is always a risk when you introduce a new vaccine or drug. But in the case of HPV, the benefits of vaccination are significant, so let’s hope there aren’t any serious unforeseen consequences for either sex.
If future studies continue to show that circumcision really does act as a kind of firewall against HIV and HPV, then in countries where there is a very high risk of these infections, perhaps adult men, rather than their parents when they were newborns, should consider circumcision. As with all surgical procedures, circumcision can have serious complications and bad outcomes—and rarely, even fatal ones. In most cases vaccination offers a considerable degree of protection. Cutting off a foreskin is not like vaccination, there’s no guarantee of immunity from infections, and, further, it may give some men and their partners a false sense of security. For now, I agree with the American Academy of Pediatrics, which states that routine circumcision is not medically justified.
FOR SOME BOYS in their early teenage years, the first sign that they have entered puberty is a swelling of their testicles. The testicles, which hang in the scrotum—essentially a sack of skin that isolates them from the rest of the body—change very little in size from the time a boy is a year old until the hormone surges of puberty kick off their next and final stage of growth. Adult testicles range in size from a small egg yolk to a large plum. Like the ovaries, the testicles do double duty as parts of both the reproductive system and the endocrine system (the system of glands responsible for production and release and hormones). They produce and store sperm, and from about the sixth week of fetal development they also pump out testosterone, the main sex hormone in males.
Each testicle is partly surrounded by the epididymis, a tightly coiled tube that leads from the testicle to the vas deferens, which is the superhighway of the sperm release program. The epididymides are entirely inside the scrotum. After the sperm are produced, they move into the epididymis, where they are stored until they leave the man’s body through ejaculation.
It’s the testicles’ role as a sperm factory that explains what at first seems to be one of the most curious features of human anatomy. Why are the keys to our gene pool (and our future generations) literally left hanging outside the body, exposed and vulnerable to injury?
The dominant theory is straightforward—sperm need to be cool.
The scrotum keeps the testicles just a little bit cooler than the rest of the body, in order to create the optimum environment for sperm t
o flourish and develop normally, a few degrees colder than the rest of the body. That theory is given some real-world support. There is evidence that high temperature, or scrotal hyperthermia is damaging to sperm. One of the first things a fertility specialist might tell men with low sperm counts is to stay away from hot tubs.
A recent study by researchers at the University of California, San Francisco, followed eleven men with fertility problems who stopped taking hot baths and getting in the Jacuzzi. Five of the eleven men, nearly half of the study group, saw their sperm counts soar almost 500 percent. And five of the six men who did not benefit from cutting out hot baths were longtime smokers, which is also known to have a negative impact on male fertility. When it comes to male fertility, the stereotypical image of the virile lady’s man puffing on a cigar in the hot tub couldn’t be further from the truth.
Hot baths and hot tubs “can be comfortably added to that list of lifestyle recommendations and ‘things to avoid’ as men attempt to conceive,” says Dr. Paul Turek, director of the UCSF Male Reproductive Health Center. Others on the list: smoking, drinking too much alcohol, marijuana, and tight underwear that holds the scrotum close to the body, giving developing sperm the “hug of death” by raising their temperature to the level of the rest of the body.
And a new study by German scientists at the University of Giessen suggests that heated car seats may deserve a place on the list too. The German team outfitted thirty men with temperature sensors on their scrotums and then sat them down on heated car seats, where they remained comfortably toasty for an hour and a half. Sure enough, the average scrotum temperature of the men who sat on heated seats was about a degree higher than the average scrotum temperature of men who sat on unheated car seats for the same period of time. Which may be just enough extra heat to toast sperm as well.
The male body actually has a very specialized climate control system for the testicles. This critical job is actually given to a very small muscle called the cremaster. When the temperature drops, the cremaster simply contracts and pulls the testicles up a little closer to the body, warming them; when they need to cool, it relaxes and the testicles drop away from the body. The cremaster muscle isn’t only activated in response to the testicles’ temperature needs. When a man is stressed, it tightens up and pulls the testicles in snug toward the body, protecting the testicles from possible physical harm.
You can actually test the “cremaster reflex.” While you’re standing, you or your partner should gently stroke the skin of the inner thigh on one leg. If you have a strong reflex, then the cremaster muscle will contract and pull up the testicle on that side of the body.
Like the cremaster, the pampiniform plexus also works to help keep the testicles cool. The pampiniform plexus is a specialized network of veins that brings venous (deoxygenated) blood back from the testicles. The pampiniform plexus acts like a countercurrent heat exchanger (in the same way your fridge or air conditioner at home works): it takes heat away from the blood that is headed to the testicles via the testicular artery. This means that the blood that supplies the testicles with oxygen reaches them at a lower temperature.
During development, testicles normally start out inside the abdomen and descend before birth. But they don’t always descend. As many as 30 percent of boys born prematurely and 3 to 4 percent of boys born full-term have at least one undescended testicle. So, if your child has an undescended testicle, it’s important to talk to your doctor about it: if left untreated an undescended testicle can permanently lose the ability to make sperm and is more likely to become cancerous. In about 65 percent of newborn boys with the condition, the testicles descend naturally by about nine months of age. If they don’t descend on their own, the condition can usually be corrected with a surgical procedure called orchiopexy or with a hormone injection.
When it comes to sexuality, a common complaint some men have regarding their testicles is the uncomfortable condition known as pelvic congestion or, more colloquially, “blue balls.” When a man is sexually aroused, there is an increase of nitric oxide in the penis, which leads to an erection. Nitric oxide is a vasodilator, which means that it causes the smooth muscle that surrounds arteries to relax, allowing the penis to flood with blood. At the same time, the veins leading away become constricted, which is what allows the increased blood flow to fill up the penis and expand it. But it’s not just the penis itself that’s affected by this process, which is called vasocongestion. The entire genital area is flooded with blood, the drainage pipes are blocked, so to speak, and everything swells. A quick way to counter this change is an orgasm: the system then shifts into reverse, the arteries constrict, the veins dilate, the flood of blood recedes, and everything returns to normal.
But, if there is no orgasm, there is no immediate signal, no narrowing arteries, and no widening veins—just a whole lot of blood sitting still in the genital region. The actual mechanics behind the testicular pain or ache that some men report after prolonged excitement without orgasm is not completely understood. One idea is simply that they ache because all the extra blood places increased pressure on the highly pain-sensitive testicles. Another related idea is that the tissue in and around those vessels becomes starved for oxygen, which is certainly known to cause pain. That’s what we believe causes angina pectoris, the chest pain caused by a lack of oxygen in the heart muscle. The word angina actually comes from the Greek “to strangle.” Whatever the cause, this much is sure—the phenomenon of blue balls is real, they really can ache—and men are not the only ones to experience this; some women actually complain of a similar effect localized to the lower pelvic region. Eventually, of course, the body realizes that there won’t be an orgasm and signals the surrounding blood vessels to begin the drainage process to restore normal blood flow. In reality, the only real blue balls found in nature belong to the African vervet monkey, which has a bright blue scrotum that looks like nothing so much as a pair of big robin’s eggs.
It has often been suggested that the size of one’s testicles has some bearing on courage or manliness. But, despite the cross-cultural popularity of this belief, size may be more connected to a species’ appetite for promiscuity.
It’s long been known that the more promiscuous females of a given species tend to be, the larger the males’ testicles relative to body size. For example, female gorillas are somewhat monogamous, and male gorillas have especially small testicles relative to their body size. Chimpanzees, on the other hand, are seriously promiscuous—and their testicles are ten times the size of those of gorillas on a relative basis. And humans? We’re comfortably—or uncomfortably?—in between.
Why the difference in testicle size? It’s all about the competition. Sperm competition, that is.
If a female mates with multiple males, the odds that any one of her partners is going to be the one who successfully gets her pregnant drop significantly because the sperm from all those other males are competing to fertilize her egg. How does the male increase his odds of passing his genes on? One way is to overwhelm the competition with numbers. Simply put, the more sperm the male can successfully ejaculate into the female, the better the chances of that male’s sperm finding their mark. And bigger testicles produce and hold more sperm.
Yet having large testicles can come at a cost—especially if you’re a bat. Scientists who studied the correlation between anatomical size and behavior in more than three hundred species of bats came to the following conclusion: “Because relatively large brains are metabolically costly to develop and maintain, changes in brain size may be accompanied by compensatory changes in other expensive tissues.”
The researchers found that in the species of bats in which the females are wanton, males were shortchanged when it came to brain size. Don’t feel sorry for the males though. They were given a big boost when it comes to reproduction. In this case, the expensive tissues they’re talking about happen to be testicles.
Scientists have found the correlation between testicle size and mating system across
the primate family, and in some other animal groups, such as birds. The more likely females are to have multiple mates when fertile, the larger male testicles are likely to be relative to body size.
But having larger testicles may not be the only way to ensure reproductive success. In 2008, scientists from the University of California at San Diego and Irvine discovered that when it comes to speed, the sperm of chimpanzees and rhesus macaques (primates that tend to be on the more promiscuous end of the spectrum) are markedly faster swimmers than human and gorilla sperm. According to Jaclyn Nascimento, one of the researchers involved in the study, “Rapidly swimming sperm cells would be evolutionarily favored when the mating pattern is polygamous, and that is consistent with our measurements of chimp and rhesus macaque sperm.”
Besides overwhelming the competition with both sheer numbers and speed, there’s another weapon in the biological arsenal used to fight promiscuity. Some primates have evolved stickier semen. Having sticky semen can work as a physiological stopper; in fact, chimpanzee semen is so thick and firm that it can actually form a plug. This is thought to come in handy when trying to block sperm from subsequent ejaculates of rival chimps. A gene found in primates called SEMG2 encodes for a protein called semenogelin II, which, like corn starch added to a thin soup, is thought to result in thicker semen. The SEMG2 gene from chimpanzees is thought to have experienced a rapid degree of evolution to keep up with the sexual competition (in this case promiscuity) that they experience on a day-to-day basis. “It’s similar to the pressures of a competitive marketplace,” says Dr. Bruce T. Lahn of the University of Chicago. “In such a marketplace, competitors have to constantly change their products to make them better, to give them an edge over their rivals—whereas, in a monopoly, there’s no incentive to change.”
How Sex Works Page 6