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Why Some Babies with Male Genes Have Female Parts

To their own surprise and that of their parents, some babies born with male genes end up with female parts.

By Jared Diamond
Jun 1, 1992 12:00 AMMay 3, 2023 5:23 PM
Woman carrying her baby girl at home


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Barbara grew up as an apparently normal girl enjoying a happy childhood. As her teenage years approached, she looked forward to experiencing the same sexual development she saw in older girls. Gradually, however, she began to have a vague sense that the expected changes weren’t happening in her. By the age of 14 she was really worried: She had not yet menstruated and her breasts showed no signs of growth. What she did have was a pain in her left groin that eventually subsided, only to be replaced by the appearance of a mass in the left side of her labia. With growing shock, she felt her voice dropping, her facial hair growing, and her clitoris enlarging to become more and more like a penis.

After Barbara’s sixteenth birthday, her penis developed erections, she produced ejaculations, and she found herself feeling a sexual interest in girls. By now she had become convinced that she was really a boy and that the mysteriously shifting mass within her was in actuality a testis. But Barbara still struggled with the problem of how to present herself to her parents and friends, before whom she avoided being caught naked. She knew they had to suspect something. When they found out, would they ridicule her — or him — as a freak?

Gender constitutes the most fundamental distinction we make among ourselves, the first question we ask when a baby is born. It establishes two radically contrasting possibilities and determines how we view ourselves and how other people view us. In almost all cultures it also establishes a division between contrasting economic and social roles. To find one’s gender ambiguous or shifting is as cruel a blow as could befall one’s ego. It’s as close as any of our children might come to the nightmare experienced by Gregor Samsa, of Franz Kafka’s terrifying story Metamorphosis, who wakes up one morning to find himself transformed into a human-size insect.

The vast majority of us are born unmistakably male or female and remain that way throughout life. We have all the sexual parts appropriate to a single gender, with no discordant pieces. It is very rare indeed that you find among humans true hermaphrodites — individuals possessing both male and female gonads.

However, there are some unfortunate individuals called pseudohermaphrodites, whose sex presents an ambiguous appearance. At the births of thousands of babies each year in the United States, the obstetrician can’t pronounce, It’s a girl! or It’s a boy! but must confess, I’m not sure what it is. Like Barbara, some appear to be born as girls but develop as boys at puberty. Some have a vagina and female external organs but lack such internal organs as ovaries and fallopian tubes; instead, they have certain male internal organs, like seminal vesicles, as well as testes hidden up in the body. 

Most of these walking mosaics of sex manage to survive this adversity: indeed, their stories are moving testimony to humans’ ability to cope with the injustice that can be dealt out by nature. But their stories are also instructive, for they shed light on a number of basic questions that concern all of us. Foremost among them are the questions: What actually determines our gender? How could the mechanisms that determine something so fundamental go so wrong? 

Ultimately, of course, our gender is laid down by our genes, which are bundled together in each cell in 23 pairs of microscopic packages called chromosomes. The 23 human chromosome pairs can be numbered and distinguished from one another by consistent differences in appearance. For chromosomes 1 through 22, the two members of the pair appear identical. Only in the case of chromosome 23, the sex chromosome, do the two representatives differ, and even then only in men, whose twenty-third chromosomes are of unequal sizes: a larger X chromosome paired with a smaller Y chromosome. Women have two paired X chromosomes instead.

What do the sex chromosomes do? Many X chromosome genes specify traits unrelated to sex, such as the ability to distinguish red and green. However, the Y chromosome contains genes specifying the development of testes. Between the fifth and seventh week after fertilization, human embryos of either sex develop an all-purpose gonad that can later become either a testis or an ovary. If a Y chromosome is present, that all-purpose gonad will begin to commit itself by the eighth week to becoming a testis. But if there’s no Y chromosome, it waits until the thirteenth week and then begins developing as an ovary. Thus the natural tendency of our primordial gonad is to develop as an ovary if nothing intervenes; something special — a Y chromosome — is required to change it into a testis.

It’s tempting to restate this simple fact in emotionally loaded terms. As developmental biologist Alfred Jost put it, Becoming a male is a prolonged, uneasy, and risky venture; it is a kind of struggle against inherent trends toward femaleness. Chauvinists might hail becoming a man as heroic, and becoming a woman as the easy fallback position. Conversely, one might regard womanhood as the natural state of humanity, with men just a pathological aberration that regrettably must be tolerated as the price for making more women. I prefer merely to acknowledge that a Y chromosome switches gonad development from the ovarian path to the testicular path, and to draw no metaphysical conclusions. 

But there’s more to a man than testes alone. A penis is among the many other obvious necessities, just as women need more than ovaries — for example, it helps to have a vagina. To form the penis, vagina, and other sex organs, the embryo is endowed with other all-purpose sexual structures besides the primordial gonad. However, unlike the case of the testes, the development of these structures is not directly specified by the Y chromosome. Instead, these structures are channeled toward male organs by secretions of the testes themselves, while a lack of testicular secretions channels them toward female organs.

For example, in the eighth week of gestation the testes begin producing the hormone testosterone, some of which gets converted into the closely related substance dihydrotestosterone, or DHT. Such hormones are called androgens. DHT goes on to convert some all-purpose embryonic structures into the glans penis, penis shaft, and scrotum. Those same structures would otherwise develop into their female equivalents: the clitoris, labia minora, and labia majora.

Embryos also start out with two sets of ducts, known as the Müllerian ducts and the Wolffian ducts. In the absence of testes the Wolffian ducts atrophy, while the Müllerian ducts grow into a female’s uterus, fallopian tubes, and the inner part of the vagina. With testes present, the opposite happens: androgens produced by the testes stimulate the Wolffian ducts to grow into a male’s seminal vesicles, vas deferens, and epididymis. At the same time, a testicular protein called Müllerian inhibiting factor does what its name implies: it prevents the Müllerian ducts from developing into the internal female organs.

Since a Y chromosome specifies testes, and since the presence or absence of the testes’ secretions specifies the remaining male or female structures, it might seem as if there’s no way that we could end up hermaphrodites. Instead, you might think, a Y chromosome should guarantee 100 percent male organs, whereas the lack of a Y chromosome should guarantee 100 percent female organs.

In fact, a long series of further biochemical steps, programmed by chromosomes other than the sex chromosomes, is required to produce all the structures other than ovaries or testes. Every step involves the synthesis of one enzyme, specified by one gene. If any one gene is altered by a mutation, the enzyme for which it’s responsible may be defective or absent. Thus, an enzyme defect may result in a male pseudohermaphrodite, defined as someone with one X and one Y chromosome, and hence intrinsically male, but with a mixture of both male and female structures.

In the pseudohermaphrodite, some male structures continue to develop normally because they depend on enzymes and hormones that remain normal. However, male structures dependent on the defective enzyme are either completely missing or replaced by their female equivalents. This can be illustrated by a discussion of two types of male pseudohermaphrodite — one resulting from a defective androgen receptor, the other from a defect in the enzyme that converts testosterone to DHT.

The former type looks like a normal woman. Indeed, she often conforms to the male ideal of feminine beauty even more than the average woman does because her breasts tend to be well developed and her legs long and graceful. Her complexion is usually flawless and she tends to have the added height of a man. Hence, cases have turned up repeatedly among female fashion models.

Since this type of pseudohermaphrodite looks like a normal baby girl at birth and externally undergoes normal development and puberty, the problem isn’t even likely to be recognized until the adolescent consults a doctor over her failure to begin menstruating. At that point the doctor discovers a simple reason for that failure: the patient has no uterus, fallopian tubes, or upper vagina. Instead, the vagina ends blindly without connecting to a uterus (although it is generally adequate for intercourse). Further examination reveals testes that are normal except for being buried in the groin or labia; they secrete normal testosterone and are programmed by a normal Y chromosome. In other words, the beautiful model is a male who happens to have a genetically determined biochemical block in the ability to respond to testosterone.

That block turns out to be in the cell receptor that would normally bind testosterone and dihydrotestosterone and thereby enable those androgens to trigger further steps in the development of male genitals. Take away that androgen receptor and all you normal male readers might look like beautiful models, too. Since the pseudohermaphrodites’ Y chromosome is normal, the testes themselves form normally and produce normal Müllerian inhibiting factor, which acts as it does in any man to forestall development of the uterus and fallopian tubes. However, the process by which the usual male machinery is activated by testosterone is interrupted. As a result, development of the remaining all-purpose embryonic sex organs follows the female channel by default: female rather than male external genitalia, atrophy of the Wolffian ducts, and hence no development of male internal genitalia.

The result, then, is a genetic male who can’t become male — in short, a genetic male whose visible sexual parts are those of a woman. Despite having a Y chromosome, hidden testes, and normal male testosterone levels, almost all such people unquestionably view themselves, and are viewed by others, as women. Most find husbands and marry. Naturally, without a uterus or ovaries, they can’t bear children, but many adopt. Most are well adjusted to their role as women and show no signs of unusual emotional stress. In these cases, not only do testes fail to make a man, but they fail to interfere with much of the happiness available to women as wives and mothers.

The second type of pseudohermaphrodite is exemplified by the case of Barbara, with which I began this article. Barbara and dozens of other similar people suffer from an enzyme defect called 5-alpha-reductase (5AR) deficiency. Like the pseudohermaphrodites with defective androgen receptors, they are genetically males, with a normal Y chromosome and testes and normal production of testosterone and Müllerian inhibiting factor. Because of this inhibiting factor they don’t develop a uterus, fallopian tubes, or the internal part of the vagina. Their external genitals appear largely female at birth, though they may be somewhat ambiguous and have some male features; this ambiguity sometimes allows babies with 5AR deficiency to be recognized at birth. At puberty, however, many of these children become much more malelike.

A mutation in the gene specifying 5AR yields a more confusing picture than does androgen receptor deficiency. In the first type of pseudohermaphrodite that we discussed, the effects of the androgens were blocked completely. But in this second type the influence of only one androgen, DHT, is affected, while the influence of the other, testosterone, is exerted normally. This is because the 5AR enzyme normally converts some testosterone into DHT; an impaired 5AR gene and enzyme mean less DHT production. Because the two androgens function somewhat separately, the result is that in 5AR-deficient pseudohermaphrodites, reproductive organs specified by testosterone are normal and only those dependent on DHT are abnormal. Ironically, the resulting blend of male and female traits has helped researchers distinguish the precise physiological roles played by testosterone and DHT in male development.

Which male traits are normal in 5AR-deficient males and hence influenced by testosterone? Because these babies are born with testes (albeit concealed in the groin or labia) and normal male internal organs (seminal vesicles, vas deferens, and epididymis), we can conclude that the growth of these structures must be triggered by testosterone secretion while the fetus is still in the womb. Hallmarks of adolescent male development that remain normal include muscle development, growth of the penis and scrotum, capacity for erections and ejaculation, and lack of breast development. These may be influenced by testosterone secretion at puberty.

At birth, though, these genetic males show numerous female traits. Their external genitals look much more like a clitoris and labia than a penis or scrotum. There is a vagina, although it ends as a blind tube. Inside, the prostate gland is small or absent. The urethra opens not at the tip of the penis/clitoris but in front of the anus and close to the vagina (which means that although these pseudohermaphrodites are able to maintain an erection and engage in intercourse, the urethra’s location ensures that the ejaculate emerges from the orifice between the legs rather than from the penis and doesn’t enter the female partner’s vagina). These features make it reasonable to assume that the normal molding of the prostate and male external genitals probably depends on DHT — which is deficient in these pseudohermaphrodites — rather than on testosterone.

At puberty these pseudohermaphrodites experience less-than-normal growth of the beard and body hair, while later on the baldness that gradually comes to characterize most older men fails to develop. These traits of normal men, then, are likely to depend on postnatal effects of DHT.

Because the 5AR gene is not on the sex chromosomes, both males and females donate a copy of it to their offspring. A single normal copy of the gene, inherited from either parent, suffices to generate enough 5AR enzyme for normal male development. Only if a male fetus inherits a defective gene from both his mother and his father will he develop as a pseudohermaphrodite with 5AR deficiency. Therefore, most known examples are clusters of related cases in remote, isolated Third World villages, where marriages between close relatives are common and children can inherit many of the same genes from both parents.

For example, one such cluster was discovered in a rural, inbred village that until 1960 had no paved road to the outside world. I’ll refer to it as Xanadu to protect the villagers’ privacy. In Xanadu, physicians have identified a total of 38 pseudohermaphrodites, all descended on at least one side from the same now-deceased woman and many of them traceable to that woman through both their mother and father. Evidently, that lady had a single copy of the mutant gene, which she passed on to many of her numerous descendants. Eventually there were enough such descendants so that some marriages within the village began to involve partners who both carried the mutant gene, thus making it increasingly likely that their children would develop as pseudohermaphrodites. In fact, of the original woman’s great-grandchildren, one turned out to be a pseudohermaphrodite; among her great-great-grandchildren, there were 6; her great-great-great- grandchildren, 14; and her great-great-great-great-grandchildren, 17.

How do such 5AR-deficient pseudohermaphrodites cope with the Kafkaesque metamorphosis that their genes force upon them? Not surprisingly, there is a wide spectrum of outcomes, depending on the biological endowment of each person, the response of the immediate family, and the response of the society. I’ll illustrate this spectrum with examples from Xanadu and another society I’ll call the Sambia, one of which found it much harder to come to terms with pseudohermaphrodites than did the other. 

For several decades in Xanadu, all pseudohermaphrodites were identified at birth as girls and were raised unquestioningly as girls. But by 1950 there had been enough cases of baby girls who became adolescent boys that the villagers began paying closer attention to newborn babies’ genitals. Since the late 1950s most pseudohermaphrodites have been recognized at birth or in childhood and raised as boys. Among the older pseudohermaphrodites, though, there were still 18 who had been reared as girls.

On reaching adulthood, only one of those 18 maintained her identity as a woman. As a teenager she married a man (who deserted her after a year), and then began to work as a housemaid and wear false breasts. The other 17 gradually became convinced of their masculinity by the changes in their bodies during adolescence. They were at first hesitant to come out as men because they feared ridicule, and indeed they did become the targets of jokes. Their families were initially astounded and confused but eventually accepted them as boys. Fifteen of them married, and a few acquired stepchildren through their wives’ former marriages. Gender roles within these 15 unions are traditional, with the male pseudohermaphrodite working at a typical man’s job involving heavy labor, while the woman keeps house, cares for a garden, and looks after any previous children that she may have had.

It’s striking how rapidly the Xanadu pseudohermaphrodites readjusted their gender role. The sex they were reared as had little effect on the age at which they passed the signposts of male adolescence, such as when they first experienced morning erections, wet dreams, masturbation, and sexual intercourse. For example, the ages for first sexual intercourse prove to be very close for pseudohermaphrodites raised as boys (15-17), pseudohermaphrodites raised as girls and switching to a male role during adolescence (15-18), and normal boys in the same village (14-16). 

Some authorities on human psychosexual development maintain that we acquire our gender identity as young children. According to this view, that identity is firmly fixed by the age of four. Among Xanadu pseudohermaphrodites, though, kids who viewed themselves unquestioningly as girls throughout most of childhood came to view themselves as men after adolescence and to dress, work, and have sex accordingly. That’s not to claim that the switch was easy, or that it left them emotionally unscarred. However, the switch was more complete and took place over less resistance from family and friends than has been the case with another group of pseudohermaphrodites whom we shall now consider.

When I began to work in the New Guinea highlands nearly 30 years ago, the highlanders were just emerging from Stone Age conditions of incessant intertribal warfare. Even more startling to me than the stone axes and heavily armed men that I met were the hostility and rigid role divisions between the sexes. Women served as beasts of burden, while unmarried men lived homosexually in communal houses to which the women only brought food. The most feared warriors, whose territory was still closed to outsiders during my early visits, were the people I’m referring to as the Sambia.

It’s an exquisitely cruel irony that one of the world’s largest known concentrations of 5AR-deficient pseudohermaphrodites, characterized by ambiguous gender, occurs among the Sambia, whose culturally imposed differences between the sexes are among the sharpest of any human society in the world. Sambia men function as fighters and hunters, women as gardeners and mothers. The men do not participate in onerous gardening work, believing that possession of a penis makes them unable to grow edible sweet potatoes. Not only are there separate footpaths for men and women within the village, but also separate living spaces for husband and wife within their small hut, marked off by planks on the floor. Children’s play after the age of about five is segregated by sex. Eventually, boys are forbidden to talk with or even glance at women, who are regarded as dirty polluters. (They have that vagina, something truly no good.) The sole acceptable position for intercourse is with the man on top, so that he can get up immediately upon ejaculating to reduce his exposure to the polluting vagina.

Alas, only women can secrete milk and grow sweet potatoes, so the Sambia father has no choice but to entrust his sons to their polluting mother’s care during early childhood. At the age of seven or so, men are at last able to take over responsibility for their sons. That’s done by forcibly initiating young boys into life in the communal men’s house, where boys and bachelor men live as a group, and where women are banned. In lieu of mother’s milk, young boy initiates are told that daily consumption of the bachelors’ semen is essential to their growing big, becoming men, and living long. Young boys fellate older ones daily until puberty, whereupon the fellators reverse roles and are fellated by the next crop of younger boys. The punishment of death is threatened for those boys who reveal the secret or those women who stumble upon it. The young boys are taught that women are harmful, so there is no room for dating or other premarital heterosexual involvement. Other unacceptable practices include male self- masturbation (semen should be ingested, not expelled, they believe) and homosexual anal intercourse.

In the absence of dating, marriages are arranged, often at birth, and consummated when the girl has her first menstrual flow. At that point the young bachelor undergoes a shock rivaling his forcible initiation into the homosexual men’s club years earlier. Heterosexual procedures are at last explained to him, and he is told to initiate them with his bride, possessor of that vagina, something truly no good. (For a look of embarrassed horror, I’ve seen nothing to rival photos taken of highland bachelors listening for the first time to an older man’s graphic explanation of sexual intercourse.) Once a man’s first child is born, homosexual activities are considered as dangerous as heterosexual activities were before his marriage. Despite this extreme flip-flop in male sexual orientation, Sambia men still manage to make the readjustment and perpetuate their tribe.

Not unexpectedly, pseudohermaphrodites, with their sexual ambiguity, don’t fit easily into Sambia life, with its sex stereotyping. In contrast to the lives of the Xanadu pseudohermaphrodites, those of their Sambia counterparts are not stories with happy endings. Most Sambia pseudohermaphrodites are raised as boys; it’s unclear whether the Sambia label such babies as boys with birth defects, or actually assign them to a third sex, called turnim man, which starts out female but is anticipated to become male. Some of the boys are rejected by their fathers or viewed with shame by their mothers. They are sometimes teased, humiliated, and subjected to cruel gossip by their peers (You don’t have a penis! Go play with the girls!). Once those who have been raised as boys are initiated into the communal men’s house, they serve as fellators but, either by choice or out of embarrassment, never as fellateds. A few obtain wives, but in at least two documented cases the wives described them as not sexually satisfying. In one study of ten adult Sambia pseudohermaphrodites, only five were married, and one committed suicide. 

A few Sambia pseudohermaphrodites are identified at birth as girls and reared as girls. Two of them were even married to men, but both were rejected in rage by their husbands after attempted intercourse. One such woman was named Moragu. On the first attempt at intercourse, Moragu’s new husband was able to penetrate only one to two inches. Similarly frustrated on a second attempt, the husband pulled back Moragu’s skirt for a closer look and was scandalized to discover testes and a small penis within the labia. After the enraged and publicly humiliated husband threatened his mate with murder, Moragu left the Sambia homeland to make a new life elsewhere.

Given the nature of Sambia society, we can hardly be surprised at its difficulties in accommodating pseudohermaphrodites comfortably. Indeed, gender ambiguity provokes nervous squirming in almost all of us — Discover authors and readers, Olympic testing committees, the general public, and even physicians. For example, it’s extremely upsetting to a physician to have to break the news to parents, We can’t figure out the sex of your child. We view gender as so fundamental and normally unambiguous — and we’re so uncomfortable even about normal sexual issues.

The pseudohermaphrodites themselves are made to feel like pariahs, mocked to their faces and whispered about behind their backs. Nearly 40 years after graduating high school, I still cringe to recall how my schoolmates stared and laughed at one unhappy classmate with ambiguous genitals whenever we took showers in the locker room. His life must have been daily torture. Nowadays there is much sympathy for patients with other types of genetic defects, but not yet for pseudohermaphrodites. The harsh fact is that gender ambiguity does arise occasionally, and it presents itself in a wide range of forms. I hope that as our scientific knowledge about pseudohermaphrodites advances, they will meet with the sympathy they deserve.

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