The Body, page 32
The vagina (Latin for “scabbard”) is the channel connecting the vulva to the cervix and uterus beyond. The cervix is a doughnut-shaped valve that stands between the vagina and the uterus. “Cervix” in Latin means “neck of the womb,” which is precisely what it is. It serves as a gatekeeper, deciding when to let substances (like sperm) in and when to let others (like blood during menstruation and babies during birth) out. Depending on the size of a man’s organ, the cervix is sometimes hit during sex, which some women find pleasurable and others find uncomfortable or painful.
The uterus is simply a more formal name for the womb, where babies grow. The uterus normally weighs two ounces, but at the end of a pregnancy it may weigh two pounds. Flanking the uterus are the ovaries, where eggs are stored, but they are also where hormones like estrogen and testosterone are produced. (Women produce testosterone, too, just not as much as men do.) The ovaries are connected to the uterus by Fallopian tubes (properly called oviducts). These are named for Gabriele Falloppio (sometimes spelled “Fallopio”), the Italian anatomist who first described them in 1561. Eggs are usually fertilized in the tube and then pushed outward into the uterus.
And there you have, very briefly, the principal pieces of sexual anatomy that are unique to women.
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Male reproductive anatomy is considerably more straightforward. It consists essentially of three external parts—penis, testicles, and scrotum—with which nearly everyone is familiar, at least conceptually. For the record, however, I will note that the testicles are factories for producing sperm and some hormones; the scrotum is the sac in which they are housed; and the penis is the delivery device for sperm (the active part of semen), as well as outlet for urine. But behind the scenes in supporting roles are other structures, known as accessory sex organs, that are much less familiar but nonetheless vital. Most men, I daresay, have never heard of their epididymis and would be a little surprised to learn that they have twelve meters of it—that’s forty feet, the length of a Greyhound bus—tucked inside their scrotal sacs. The epididymis is fine tubing, neatly coiled, in which sperm mature. The word is from the Greek for “testicles” and, a touch surprisingly, was first used in English by Ben Jonson in his play The Alchemist in 1610. He was presumably showing off because no one in the audience was likely to know what he meant by it.
Similarly obscure but no less important are the other accessory sex organs: bulbourethral glands, which produce a lubricating fluid, and are sometimes also known as Cowper’s glands after their seventeenth-century discoverer; seminal vesicles, where semen is in large part produced; and the prostate, which everyone has at least heard of, though I have yet to meet a layman under fifty who knows quite what it does. The prostate, it might be said, produces seminal fluid throughout a man’s adulthood and anxiety in his later years. We shall discuss this latter attribute in a later chapter.
One perennial mystery of male reproductive anatomy is why the testicles are on the outside, where they are exposed to trauma. It is usually said that it is because testicles function better in cooler air, but this overlooks that many mammals get along perfectly well with their testicles on the inside: elephants, anteaters, whales, sloths, and sea lions, to name but a few. Temperature regulation may indeed be a factor in testicular efficiency, but the human body is perfectly capable of dealing with that without leaving the testicles so disconcertingly vulnerable to harm. Ovaries, after all, are kept safely hidden away.
There is also a great deal of uncertainty over what is normal in terms of penis size. In the 1950s, the Kinsey Institute for Sex Research recorded the average length of the erect penis at 5 to 7 inches. By 1997, a sample of over a thousand men put it at 4.5 to 5.75 inches, a fairly notable demotion. Either men are shrinking, or there is a great deal more variability in penis size than has traditionally been allowed. The bottom line is that we don’t know.
Sperm appears to have enjoyed (if that is the word) more careful clinical study, almost certainly because of concerns about fertility. Authorities seem to be universally agreed that the average quantity of semen released at orgasm is 3 to 3.5 milliliters (about a teaspoonful), with an average spurt distance of seven to eight inches, though according to the British scientist and writer Desmond Morris a launch of three feet has been scientifically recorded. (He does not specify the circumstances.)
The most interesting experiment involving sperm was almost certainly that undertaken by Robert Klark Graham (1906–97), a California businessman who made a fortune manufacturing shatterproof lenses for eyeglasses and then in 1980 founded the Repository for Germinal Choice, a sperm bank that promised to stock the sperm only of Nobel laureates and others of exceptional intellectual stature. (Graham modestly included himself among the select worthies.) The idea was to help women produce babies of genius by giving them the very best sperm modern science could provide. Some two hundred children were born as a result of the bank’s efforts, though none, it seems, proved to be an outstanding genius or even an accomplished eyeglass engineer. The bank closed in 1999, two years after the death of its founder, and, all in all, does not seem to have been greatly missed.
*1 For most of his career, he was just plain Wilhelm Waldeyer. The more effusive title came in 1916, near the end of his life, when he was ennobled by the German state.
*2 Other geneticists, it is worth noting, have suggested that the extinction could happen in as little as 125,000 years or as much as 10 million.
18 IN THE BEGINNING: CONCEPTION AND BIRTH
To begin my life with the beginning of my life, I record that I was born.
—CHARLES DICKENS, DAVID COPPERFIELD
IT’S A LITTLE hard to know what to make of sperm. On the one hand, they are heroic: the astronauts of human biology, the only cells designed to leave our bodies and explore other worlds.
But on the other hand, they are blundering idiots. Shoot them into a womb and they seem curiously ill-prepared for the one task evolution has given them. They are terrible swimmers and appear to have almost no sense of direction. Unaided, it could take a sperm ten minutes to swim across a space the width of one of the words on this page. That’s why a male orgasm is such a vigorous endeavor. What seems to the man purely a burst of pleasure really is a kind of rocket launch. Once the sperm are expelled, it isn’t known whether they move about randomly until one strikes lucky or whether they are drawn to the waiting egg by some chemical signal.*1
In either case, overwhelmingly they fail. The chances of a successful fertilization from a single randomly timed act of sex have been calculated to be only about 3 percent. And matters seem to be getting worse across the Western world. About one in seven couples now seek help in conceiving.
Several studies have reported serious falls in sperm counts in recent decades. A meta-analysis in the journal Human Reproduction Update, based on 185 studies over nearly forty years, concluded that sperm counts in Western nations fell by more than 50 percent between 1973 and 2011.
Among the suggested causes have been diet, lifestyle, environmental factors, frequency of ejaculation, and even (seriously) wearing tight underpants, but no one knows. In a New York Times article titled “Are Your Sperm in Trouble?,” the columnist Nicholas Kristof concluded that, yes, they probably are and attributed it to “a common class of chemical called endocrine disruptors, found in plastics, cosmetics, couches, pesticides and countless other products.” He suggested that the average young man’s sperm in the United States is about 90 percent faulty. Other studies in Denmark, Lithuania, Finland, Germany, and elsewhere have reported sharp falls in sperm counts.
Richard Bribiescas, a professor of anthropology, ecology, and evolutionary biology at Yale, believes that many of the reported counts are dubious and that even if correct there is no reason to suppose that there has been a decline in overall fertility. Diet and lifestyle, body temperature at the time of testing, and frequency of ejaculation are all likely to influence sperm counts, and the totals may vary widely over time in the same person. “Even if modest declines in sperm count have indeed occurred, there is no reason to believe that male fecundity has been compromised,” Bribiescas wrote in Men: Evolutionary and Life History.
The fact is, it is really hard to say because there is such enormous variability in sperm production among healthy men anyway. The number of spermatozoa produced by the average man in the prime of life varies from 1 million to 120 million per milliliter, with an average of about 25 million per milliliter. The average ejaculation is about three milliliters, which means that a typical sex act produces enough sperm to repopulate a medium-sized country at the very least. Why there is such a broad range of wriggling potentiality, and indeed why such an extravagance of production even at the lower end when only one sperm is required for conception, are questions that science has yet to answer.
Women likewise are endowed with a massive surplus of reproductive possibility. It is a curious fact that every woman is born with her lifetime’s supply of eggs already inside her. They are formed when she is still in the womb and sit in the ovaries for years and years before being called into play. As noted in the previous chapter, the idea of women being born with a full load of eggs—the formal name is ova—was first suggested by the great and busy German anatomist Heinrich von Waldeyer-Hartz, but even he would have been astonished at just how quickly and abundantly eggs are formed within the growing child. A twenty-week-old fetus will weigh no more than three or four ounces but will already have 6 million eggs inside her. That number falls to 1 million by the time of birth and continues to fall, though at a slower rate, through life. As she enters her childbearing years, a woman will have about 180,000 eggs primed and ready to go. Why she loses so many eggs along the way and yet enters her childbearing years with vastly more than she will ever need are two of life’s many imponderables.
The bottom line is that as a woman ages, the number and quality of her eggs diminishes, and that can be a problem for those who postpone childbirth to the later stages of their productive years, which is exactly what is happening throughout the developed world. In six nations—Italy, Ireland, Japan, Luxembourg, Singapore, and Switzerland—the average age of women at their first birth is now over thirty, and in six others—Denmark, Germany, Greece, Hong Kong, the Netherlands, and Sweden—it is just under. (The United States is an outlier here. The average age of women at first birth there is 26.4, the lowest among rich nations.) Buried within these national averages are even greater variations within social or economic groupings. In Britain, for instance, the average age for women at first birth is 28.5 years, but for university graduates it is 35. As Carl Djerassi, the father of the contraceptive pill, noted in an essay in The New York Review of Books, by the age of thirty-five a woman’s stock of eggs is 95 percent exhausted and those that remain are more liable to produce faults or surprises, like multiple births. Once women pass thirty, they are much more likely to have twins. The one certainty of procreation is that the older both parties get, the more difficulty they are likely to have conceiving, and the more problems they may encounter if they do conceive.
One intriguing paradox of reproduction is that women are having babies later but preparing for it earlier. The age of first menstruation for women has fallen from fifteen in the late nineteenth century to just twelve and a half today, at least in the West. That is almost certainly because of improved nutrition. But what cannot be explained is that the rate has accelerated even further in more recent years. Just since 1980, the age of puberty has fallen in America by eighteen months. About 15 percent of girls now begin puberty by age seven. That could be a reason for alarm. According to the Baylor University Medical Center Proceedings, evidence suggests that the prolonged exposure to estrogen substantially increases the risk of breast and uterine cancer in later life.
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But let us suppose, for the sake of a happy narrative, that one hardy or lucky spermatozoon has reached the waiting egg. The egg is one hundred times larger than the sperm it pairs with. Fortunately, the sperm doesn’t have to force its way in, but is welcomed like a long-lost if curiously diminutive friend. The sperm passes through an outer barrier called the zona pellucida and, all being well, fuses with the egg, which immediately activates a kind of electrical force field around itself to stop other sperm from getting through. The DNA from sperm and egg are combined into a new entity called a zygote. A new life has begun.
Success from this point is by no means assured. Perhaps as many as half of all conceptions are lost without being noticed. Without this, the rate of birth defects would be 12 percent instead of 2 percent. About 1 percent of implanted eggs end up stuck in the Fallopian tube, or somewhere else other than the womb, in what is known as an ectopic pregnancy (from a Greek word meaning “wrong place”). This can be very dangerous even now. Once it was a death sentence.
But if all goes well, within a week the zygote has produced ten or so cells known as pluripotent stem cells. These are the master cells of the body and one of the great miracles of biology. They determine the nature and organization of all the billions of cells that transform a little ball of possibility (known formally as a blastocyst) into a functioning and adorable little human (known as a baby). This moment of transition, when cells begin differentiating, is called gastrulation and has been described many times as the most important event of your life.
The system isn’t perfect, however, and occasionally a fertilized egg splits to form identical (or monozygotic) twins. Identical twins are clones: they share the same genes and normally are very alike in appearance. They are in contrast to fraternal (or dizygotic) twins, which result when two eggs are produced in the same ovulation and both are fertilized by separate spermatozoa. In that case, the two babies develop side by side in the womb and are born together but are no more alike than any other two siblings. About one in 100 natural births result in fraternal twins, one in 250 in identical twins, one in 6,000 in triplets, and one in 500,000 in quadruplets, but fertility treatments greatly increase the likelihood of multiple births. Twins and other multiples are about twice as common today as they were in 1980. Women who have had twins already are ten times more likely to produce a second set than women who have not.*2
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Now things speed up considerably. After three weeks, the budding embryo has a beating heart. After 102 days, it has eyes that can blink. In 280 days, you have a new child. Along the way, at about eight weeks, the developing infant stops being called an embryo (from Greek and Latin words meaning “swollen”) and starts being a fetus (from the Latin for “fruitful”). Altogether it takes just forty-one cycles of cell divisions to get from conception to a fully formed little human.
For much of this early period, the mother is likely to suffer from morning sickness, which, as almost any pregnant woman can tell you, doesn’t happen just in the morning. About 80 percent of mothers-to-be suffer nausea, especially during the first three months, though for an unlucky few the condition can last for the whole nine months. Sometimes it becomes so severe that it gets a medical name: hyperemesis gravidarum. In such cases, it may require hospitalization. The most common theory for why women suffer morning sickness is that it encourages them to eat cautiously during the early stages of pregnancy, though that fails to explain why morning sickness then usually stops after a few weeks, when women should still probably be conservative in their food choices, or why women who eat a safe and bland diet get sick anyway. A big part of the reason that there are no cures for morning sickness is that the tragic experience in the 1960s of thalidomide, which was designed to combat morning sickness, left pharmaceutical companies permanently reluctant to try to make drugs of any type for pregnant women.
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The business of pregnancy and birth has never been easy. However tedious and painful childbirth is now, it was much worse in the past. Until the modern era, levels of care and expertise were often pretty appalling. Just determining whether a woman was pregnant was a long-standing challenge for medical men. “We have known a practitioner of thirty years’ standing blister the abdomen in the ninth month under the idea that he was treating a morbid growth,” wrote one authority as late as 1873. The only truly reliable test, one doctor noted drily, was to wait nine months and see if a baby emerged. Medical students in England weren’t required to study any part of obstetrics until 1886.
Women who suffered from morning sickness and were rash enough to declare it were likely to be bled, given enemas, or dosed with opiates. Women were sometimes bled even if they had no symptoms at all, as a precaution. They were also encouraged to loosen their corsets and to abjure “conjugal enjoyments.”
Almost anything to do with reproduction was considered suspect—pleasure above all. In a popular book of 1899, What a Young Woman Ought to Know, Mary Wood-Allen, an American doctor and social reformer, told women that they could engage in conjugal relations within marriage so long as it was done “without a particle of sexual desire.” In the same period, surgeons developed a new procedure called an oophorectomy—the surgical removal of the ovaries. For a decade or so, it was the operation of choice for well-off women with menstrual cramps, back pain, vomiting, headaches, even chronic coughing. In 1906, an estimated 150,000 American women underwent oophorectomies. It more or less goes without saying that it was an entirely pointless procedure.
