In this assignment, you will critically evaluate articles in the field of adult development. Each week, you will read two articles from the Annual Editions: Human Development textbook (see the weekly readings for the chosen articles). For each article, do

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Article 2 The Incredible Expanding Adventures of the X Chromosome

CHRISTOPHER BADCOCK

Genes housed on the powerhouse x chromosome shed new light on the human mind, including why identical female twins differ more than their male counterparts, why there are more male geniuses and male autists, and why you may have mom to thank for your brains.

In the early 1980s I met and began an unofficial training with Anna Freud—Sigmund Freud’s youngest daughter, and his only child to follow him into psychoanalysis. I was a young social scientist who had been carrying out a self-analysis for some years.

Anna Freud’s couch was a daybed on which I lay, with her seated in a chair at its head. On one or two occasions I couldn’t help but think that the voice I heard coming from her chair was in fact that of her father, speaking to me from beyond the grave.

I can even recall her exact words in one case. I had been free-associating about my attempt to analyze myself when Anna Freud remarked, “In your self-analysis you sank a deep but narrow shaft into your unconscious. Here we clear the whole area, layer by layer.” This produced a spine-tingling reaction in me, and I surprised Miss Freud (as I called her) by stating that her remark reminded me of her father, because he was particularly fond of archaeological metaphors in his published writings. Most people would simply attribute her statement to the influence of her father’s writing on her own choice of words. Thirty years ago, I would probably have said the same. But today, having spent decades researching the links between genetics and psychology, I can offer a different hypothesis, one that goes to the core of all we now know about the inheritance and expression of genes in the brain.

The Royal X

Everyone inherits 23 chromosomes from each parent, 46 in all, making 23 matched pairs—with one exception. One pair comprises the chromosomes that determine sex. Female mammals get an X chromosome from each parent, but males receive an X from their mother and a Y sex chromosome from their father.

The X chromosome a woman inherits from her mother is, like any other chromosome, a random mix of genes from both of her mother’s Xs, and so does not correspond as a whole with either of her mother’s X chromosomes. By contrast, the X a woman inherits from her father is his one and only X chromosome, complete and undiluted. This means that a father is twice as closely related to his daughter via his X chromosome genes as is her mother. To put it another way: Any X gene in a mother has a 50/50 chance of being inherited by her daughter, but every X gene in a father is certain to be passed on to a daughter.

These laws of genetic transmission have major implications for family lineages. When it comes to grandparents, women are always most closely X-related to their paternal grandmother and less related to their paternal grandfather. Consider how this plays out in the current British royal family. The late Diana, Princess of Wales, will be more closely related to any daughter born to William and Kate than will Kate’s parents, thanks to William’s passing on his single X from her. Kate’s mother’s X genes passed on to a granddaughter, by contrast, will be diluted by those of Kate’s father in the X this girl would receive from Kate, meaning that the X-relatedness of the Middletons to any granddaughter would be half that of Princess Diana. Prince Charles, however, would be the least related of all four grandparents to Prince William’s daughters because he confers no sex chromosome genes on them.

Prince Charles would be the least related grandparent to any daughters of prince William and Kate because he confers no sex chromosome to girls.

Of course, if William and Kate produce a son, the situation is reversed, and now Prince Charles is most closely related to his grandson, via his Y chromosome. Princess Diana will have no sex-chromosome relatedness to William and Kate’s sons because the X she bequeathed William will not be passed on to the grandsons.

Calculations of X-relatedness may seem abstract, but they have probably played a huge role in European history, thanks to the fact that Queen Victoria passed on hemophilia, an X-chromosome disorder that was in the past fatal to males. Victoria and her female descendants were protected by a second, unaffected X, but princes in several European royal houses—not least the Romanovs—were affected, with disastrous consequences for successions based on male primogeniture.

The X in Sex

Not only are X chromosomes bequeathed and inherited differently, depending on whether you are male or female, they also have different patterns of expression in the body. For example, in 1875, Darwin described a disorder that appeared in each generation of one family’s male members, affecting some but sparing others: “… small and weak incisor teeth … very little hair on the body … excessive dryness of the skin. … Though the daughters in the … family were never affected, they transmit the tendency to their sons; and no case has occurred of a son transmitting it to his sons.”

Today we know this to be anhidrotic ectodermal dysplasia (AED), a disorder involving sweat glands, among other things, that affects males and females differently. Because AED is carried on an X chromosome, affected males have no sweat glands whatsoever. They express their one and only X in all their cells. Affected females with the AED gene on only one X have different patterns of expression because areas of their body randomly express one or the other of their two X chromosomes. It is perfectly possible for an affected woman to have one armpit that sweats and one that doesn’t.

X chromosome expression can explain not only differences between males and females but also differences between identical female twins. Such twins may routinely differ more than their male counterparts, because in each woman, one of their two X chromosomes is normally silenced. Identical twins result when the cells of the fertilized egg have divided only a few times and the egg then splits into two individuals. The pattern of differential X expression in cells is set at this stage. In females, an X chromosome gene called Xist effectively tosses a coin and decides which of the two X chromosomes will be expressed and which silenced in any particular cell.

Differential X chromosome gene expression explains why one of a pair of living Americans is a successful athlete yet her identical twin sister suffers from Duchenne muscular dystrophy (DMD), an X-linked genetic disease that predominantly affects males and leaves sufferers unable to walk. In this case only one twin was unfortunate enough to inherit the cell lineages that expressed the DMD gene from one parental X chromosome, while the other twin inherited those expressed from the other parent’s unaffected X.

A predisposition to sex-linked disorders is just one of the ways female identical twins differ more than males. A recent study found that compared with male twins, female identical twins vary more on measures of social behavior and verbal ability. This is also due to differential expression of genes on their two X chromosomes in contrast to male twins’ single, truly identical X. In the past, such differences between identical twins would have been attributed to nongenetic or environmental factors, but now we know that these dissimilarities are in fact the result of gene expression. Where X chromosome genes are concerned, what once seemed to be nurture now turns out to be nature.

The X Factor in IQ

Another important factor in sex chromosome expression is the huge dissimilarity between the information carried on the X and Y chromosomes. The Y has a mere 100 or so genes, and there is no evidence that any of them are linked to cognition. This contrasts sharply with the 1,200-odd genes on the X chromosome. There is mounting evidence that at least 150 of these genes are linked to intelligence, and there is definite evidence that verbal IQ is X-linked. It suggests that a mother’s contribution to intelligence may be more significant than a father’s—especially if the child is male, because a male’s one and only X chromosome always comes from his mother. And in females, the X chromosome derived from the father is in fact bequeathed directly from the father’s mother, simply setting the maternal X-effect back one generation, so to speak.

The fact that males have only a single X, uniquely derived from the mother, has further implications for variations in intelligence. Look at it this way: If you are the son of a highly intelligent mother and if there is indeed a major X chromosome contribution to IQ, you will express your one and only maternal X chromosome without dilution by the second X chromosome that a female would inherit. The effects cut both ways: If you are a male with a damaged IQ-linked gene on your X, you are going to suffer its effects much more obviously than a female, who can express the equivalent, undamaged gene from her second X chromosome. This in itself likely explains why there are more males than females with very high and very low IQs: males’ single X chromosome increases variance in IQ, simply because there is not a second, compensatory X chromosome.

If you are the son of a highly intelligent mother and there is indeed a major X chromosome contribution to IQ, you’re in luck.

The inheritance of intelligence is not limited to the influence of sex-linked genes. Non-sex-chromosome genes can also vary in their pattern of expression depending on which parent they come from (so-called genomic imprinting). One such gene on chromosome 6 (IGF2R) has been found to correlate with high IQ in some studies. The mouse version of this gene is expressed only from the maternal chromosome, and to that extent such genes resemble X chromosome ones in their maternal bias. Although it remains highly controversial to what extent the same is true of the human version of this gene, several syndromes that feature mental retardation are associated with imprinted genes on others of the 22 non-sex chromosomes.

The Case Against “Genius” Sperm Banks

IF INTELLIGENCE IS X-linked to the degree that some researchers speculate, there are important implications for our views of the heritability of talent—and even genius. The Repository for Germinal Choice was a California sperm bank that operated in the 1980s and 1990s and claimed that its donors reflected a range of Nobel laureates. (In fact the only confirmed Nobel Prize-winning donor was William Shockley, and most donors are now known not to have been laureates at all.) But beyond the actual composition of the sperm bank, there is a fundamental problem with an enterprise founded on the belief that Nobel Prize-winning talent might be heritable from the father, given the likely role of the X chromosome in intelligenc.

In the case of a “genius” sperm bank, only half the sperm donated would on average be carrying the Nobel laureate’s X chromosome, and any child resulting from such a fertilization would be female, and so would have a second X from the mother to dilute its effect. In the beginning, mothers receiving Nobel laureates’ sperm from the Repository for Germinal Choice had to be members of Mensa, and so would have had high IQs to pass on to their offspring of either sex via their X chromosomes. Indeed, this in itself might explain any apparent heritability of Nobel laureate “genius” via the Repository.

The other half of the preserved sperm would have a Y chromosome instead of an X. These sperm assuredly would produce sons, but there is no evidence that the Y is implicated in intelligence. On the contrary, the sole X of sons conceived this way would increase their vulnerability to intellectual impairment in the way that it does for all males, and would also mean that any “genius” seen in them most likely came from their single, undiluted maternal X.

Finally, there is the environmental factor in IQ. Clearly this too would be wholly attributable to the mothers in the case of a sperm bank, because the father provides only his genes.

Ironically then, mothers with children of “genius” sperm-bank fathers were probably laboring under something of a delusion. Any intellectual talent in their children was most likely predominantly attributable to them, both via their X chromosome genes and the home environment they provided. However, the single mothers who nowadays constitute the major clientele for sperm banks may not be too displeased to realize that, where heritability of intelligence is concerned, Mother Nature is something of a feminist.

X Expression in Autism

Autism spectrum disorder is yet another phenomenon that can be clarified through the prism of X chromosome inheritance and expression. Researchers have recently begun to suspect that autism is X-linked, in part because more males than females are affected by ASD, particularly at the high-functioning end of the spectrum—Asperger’s syndrome—where males outnumber females by at least 10 to 1. Asperger’s syndrome impairs pro-social behavior, peer relations, and verbal ability (among other deficits)—the very same traits that vary between identical female as opposed to identical male twins, and all of which are thought to have some linkage to the X chromosome. Because males have only a single X, they could be much more vulnerable to such X-linked deficits than are females, who normally have a second X chromosome to compensate and dilute the effect.

Indeed, women afflicted with autism spectrum disorders may be among the minority of females who disproportionately express one parent’s X. Women on the autism spectrum are probably among the 35 percent of women who have a greater than 70:30 skew in their pattern of X expression in favor of one rather than the other parent’s X. Indeed, 7 percent of women have more than a 90:10 skew. Such a hugely one-sided expression of one X would closely resemble the single X chromosome found in males. And if X expression peculiarities affect critical genes implicated in autism in the case of these women, Asperger’s would result, just as it does in males. Furthermore, the fact that only a small minority of females have such highly skewed X expression could explain why so many more males than females are affected. Most females have more equitable patterns of X expression and are therefore protected by their second X.

The peculiarities of X chromosome gene expression might even explain the often-remarked variability of the symptoms in Asperger’s. Classically heritable single-gene disorder like anhidrotic ectodermal dysplasia or Duchenne muscular dystrophy usually have strikingly consistent symptoms because only one gene is affected, often in the same way. But if variable expression of several X-linked genes is the norm in Asperger’s syndrome, the outcome in each case might be surprisingly different, and the combined effects highly variable—just as researchers find.

Female identical twins differ more than their male counterparts, because in each woman one of their two X chromosomes is normally silenced.

X Marks the Spot in the Brain

What light might this shed on Anna Freud’s eerie use of metaphors favored by her father? In her case, the woman who became a psychoanalyst just like her father might have been among the minority of women who disproportionately express one parent’s set of X-linked genes in the brain. We saw earlier that anhidrotic ectodermal dysplasia affects only some areas of a woman’s skin, depending on where the affected X is expressed. Both the skin and the brain develop from the same layer in the ball of cells (or blastocyst) from which the embryo first forms. We also saw that in females this can result in some cells expressing one parent’s X and some expressing the other’s, and if this can happen to the skin, then it could also occur in the brain: Some parts might express the father’s X and some parts the mother’s. Indeed, there is persuasive evidence that this occurs in mice, and circumstantial evidence that it also does in humans.

Given the possibility of an extreme skew in the pattern of X expression, such as likely occurs in women with Asperger’s syndrome, we can envisage a situation in which critical parts of a woman’s brain are built entirely by one parent’s genes. And if that parent is the father, then the same genes that constructed his brain would be expressed in his daughter’s brain. Theoretically, a woman could be an X chromosome clone of her father in that each and every X gene he has would be inherited and expressed by her, perhaps in exactly the same regions of the brain. This could result in a daughter’s mind being very like her father’s—and surprisingly dissimilar to her mother’s.

Freud emphasized the importance of the relationship between mothers and sons, but in my experience it pales in comparison to that between many fathers and daughters, who often seem to have a close emotional bond that intensifies with time.

Sigmund Freud’s own relationship with his daughter Anna certainly seems a case in point, as I was able to observe firsthand—at least in the daughter at the end of her life. At the time, I felt I was hearing the voice of Freud speaking from beyond the grave. But of course only a person’s DNA can survive his or her death, and even then it has to be packaged in a living descendant. So today I am more inclined to think that the words I heard may indeed have been those of Sigmund Freud, but expressed from his daughter’s paternal X chromosome.

Article 4 Unnatural Selection

MARA HVISTENDAHL

The gaping gender gap in Asia-the result of sex-selective abortion—has a burgeoning (and to some, equally alarming) counterpart here in the U.S.

New Delhi, India

For Dr. Puneet Bedi, the intensive care unit in Apollo Hospital’s maternity ward is a source of both pride and shame. The unit’s technology is among the best in Delhi—among the best, for that matter, in all of India. But as a specialist in high-risk births, he works hard so that babies can be born. The fact that the unit’s technology also contributes to India’s skewed sex ratio at birth gnaws at him. Seven out of 10 babies born in the maternity ward, Bedi says, are male. He delivers those boys knowing that many of them are replacements for aborted girls.

A tall, broad-shouldered man with a disarmingly gentle voice, Bedi stands in the unit’s control room, gazing into a sealed, temperature-controlled room lined with rows of cribs. He performs abortions himself. For sex-selective abortions, however, he reserves a contempt bordering on fury. To have his work negated by something as trifling as sex preference feels like a targeted insult. “You can choose whether to be a parent,” he says. “But once you choose to be a parent, you cannot choose whether it’s a boy or girl, black or white, tall or short.”

A broad interpretation of parental choice, indeed, is spreading throughout India—along with China, Taiwan, Vietnam, Georgia, Azerbaijan, and Albania. Preliminary results from India’s 2011 census show a sex ratio of only 914 girls for every 1,000 boys ages 6 and under, a decline from 2001. In some Chinese counties the sex ratio at birth has reached more than 150 boys for every 100 girls. “We are dealing with genocide,” Bedi says. Sex-selective abortion, he adds, is “probably the single most important issue in the next 50 years that India and China are going to face. If you’re going to wipe out 20 percent of your population, nature is not going to sit by and watch.”

If you’re going to wipe out 20 percent of your population, nature will not sit by and watch.

Bedi speaks with an immaculate British accent that hints at years spent studying at King’s College London. The accent helps in this part of Delhi, where breeding can trump all else. His patients are the sort who live in spacious homes tended by gardeners, belong to bucolic country clubs, and send their children to study in the United States. India’s wealthy are among the most frequent practitioners of sex selection, and in their quest to have a son Bedi is often an obstacle. His refusal to identify sex during ultrasound examinations disappoints many women, he says: “They think it’s just a waste of time and money if you don’t even know whether it’s a boy or a girl.”

India outlawed fetal sex identification and sex-selective abortion in 1994, but so many physicians and technicians break the law that women have little trouble finding one willing to scan fetal sex. Bedi says sex-selective abortion has caught on in Delhi because it bears the imprint of a scientific advance. “It’s sanitized,” he says. The fact that sex selection is a medical act, he adds, neatly divides the moral burden between two parties: Parents tell themselves their doctor knows best, while doctors point to overwhelming patient demand for the procedure.

Hospital administrators, for their part, have little incentive to do anything about the problem because maternity wards bring in substantial business. (At Apollo, a deluxe delivery suite outfitted with a bathtub, track lighting, a flat screen television, and a large window looking out onto landscaped grounds runs to $200 a night.) “When you confront the medical profession, there is a cowardly refusal to accept blame,” Bedi says. “They say, ‘We are doctors; it’s a noble profession.’ This is bullshit. When it comes to issues like ethics and morality, you can have an opinion, but there is a line which you do not cross, Everybody who [aborts for reasons of sex selection] knows it’s unethical. It’s a mass medical crime.”

For as long as they have counted births, demographers have found an average of 105 boys born for every 100 girls. This is our natural sex ratio at birth. (The small gap neatly makes up for the fact that males are more likely to die early in life.) If Asia had maintained that ratio over the past few decades, the continent would today have an additional 163 million women and girls.

For Westerners, such a gender gap may be difficult to fathom: 163 million is more than the entire female population of the United States. Walk around Delhi’s posh neighborhoods, or visit an elementary school in eastern China, and you can see the disparity: Boys far outnumber girls.

At first glance, the imbalance might seem to be the result of entrenched gender discrimination and local practices. Scholars and journalists typically look to the Indian convention of dowry, which makes daughters expensive, and to China’s one-child policy, which makes sons precious, to explain sex selection in Asia. (Sons have long been favored in China, as in many other parts of the world.) But this logic doesn’t account for why South Koreans also aborted female fetuses in large numbers until recently, or why a sex ratio imbalance has lately spread to the Caucasus countries—Azerbaijan, Georgia, and Armenia—and the Balkans, or why sex-selective abortion occurs among some immigrant communities in the United States.

What impact will hundreds of million of “surplus” men have on everything from health care to crime?

The world’s missing females are an apparent paradox: Sex selection is occurring at a time when women are better off than ever before. “More and more girls are going to school and getting educated,” says T.V. Sekher, a demographer at the International Institute for Population Studies in Mumbai. And in India, educated women are more likely to have a son than those with no degree. The women who select for sex include lawyers and doctors and businesspeople. Economic development has accompanied a drop in fertility rates, which decreases the chances of a couple getting the son they want without resorting to technology.

We might have seen this coming. Decades ago, Western hysteria over what many saw as an impending “population explosion” led American scholars and policymakers to scour the world for solutions to reducing the global birth rate. Studies from India and East Asia showed the major barrier to acceptance of contraception was that couples wanted at least one son. The advocates of population control saw that the barrier might be turned into an opportunity, however: If parents could be guaranteed a son the first time around, they might happily limit themselves to one or two children.

Beginning in the late 1960s, influential U.S. experts sounded their approval for sex selection everywhere from the pages of major scientific journals to the podiums at government sponsored seminars. “[I]f a simple method could be found to guarantee that first-born children were males,” Paul Ehrlich wrote in The Population Bomb in 1968, “then population control problems in many areas would be somewhat eased.”

Meanwhile, another group of scientists was figuring out how to determine fetal sex. These scientists’ efforts focused on amniocentesis, which entails inserting a needle through a pregnant women’s abdomen into the amniotic sac surrounding the fetus and removing a small amount of protective amniotic fluid, a substance rich with fetal cells that reveal its sex. They saw sex determination as a way to help women carrying sex-linked diseases like hemophilia have healthy children. But when amniocentesis, and later ultrasound, found their way to Asia decades later, it was their use as a population-control tool that stuck.

Sex selection’s proponents argued that discrimination against women and girls wouldn’t endure. As women became scarce, several prominent Western theorists proposed, they would also become more valuable, prompting couples to have daughters again. But in fact the opposite has happened. In their scarcity, women are being turned into commodities to be sold to and exploited by what demographers call “surplus men”: the ones left over in an imagined world in which everyone who can marry does so. Scholars have begun to calculate the impact hundreds of millions of such men will have on everything from health care to crime.

Suining County, China

In a village in eastern China’s agricultural belt, I meet Zhang Mei, a 37-year-old woman clad in men’s pants and a black-and-white polka-dot shirt that billows around her thin frame. Zhang is from distant Yunnan province, a poor mountain region near the border with Tibet. Her neighbors say she arrived 20 years ago, after a long journey in which a trafficker took her east to deliver her into marriage. She had no idea where she was headed beyond the vague promise that she would find work there, and yet she had some faith in the trafficker, for she hadn’t been kidnapped. Her parents had sold her.

The man who became her husband was gentle, but 15 years her senior, undeniably ugly, and one of the poorest residents of the village. Zhang learned that she had to work hard to make ends meet, and that she could not leave, even for a short trip home. Soon after she married, she found herself under pressure to have a son. One came on the third try, after two girls. But as the children grew, her husband complained it cost too much to educate their daughters, and since it is sons that matter in Suining, he sent one of the girls back to Yunnan to be raised by Zhang’s parents: a return, one generation later, of a lost girl.

Today Zhang copes with lifelong detention by gambling at raucous majiang games, burying herself in soap operas, and praying. (She is Christian.) “I carry some burdens,” she tells me, as we sit on the couch in her one-room home. “If I didn’t pray, I would keep them all in my heart.”

Zhang’s story is perhaps the most obvious way in which the gender imbalance is altering societies in Asia. The U.S. Department of State lists the dearth of women in Asia as one of the principal causes of sex trafficking in the region. Some of those women, like Zhang, are sold into marriage. Others become prostitutes. But what happens to the men who can’t find partners is significant as well.

Nothing can fully predict the effect of gathering tens of millions of young bachelors in one place for years on end. But preliminary conclusions can be drawn from places where the first generation touched by sex selection has reached adulthood. One line of speculation centers on testosterone, which occurs in high levels among young unmarried men. While testosterone does not directly cause violence in a young man, it can elevate existing aggressive tendencies, serving as a “facilitative effect” that predicts whether he will resort to violence. Gauging whether millions of high-testosterone men together spark more violence is complicated, particularly in China and India, which have experienced great social change in the past few decades. But some answers can be found through breaking down crime rates by region and time period.

In a 2007 study, Columbia University economist Lena Edlund and colleagues at Chinese University of Hong Kong used the fact that China’s sex ratio at birth spiked in some provinces earlier than others to explore a link between crime rates and a surplus of men. The researchers found a clear link, concluding a mere 1 percent increase in sex ratio at birth resulted in a 5-to 6-point increase in an area’s crime rate.

Other scholars speculate the gender imbalance is yielding depression and hopelessness among young men-which may explain why China has lately been hit with the sort of senseless violence that was once America’s domain. In 2004 and 2010 the country saw separate waves of attacks on elementary schools and child care centers in which murderers went on rampages and bludgeoned and stabbed children to death.

Eight out of the 10 killers (all male) lived in eastern Chinese provinces with high sex ratios at birth; several were unemployed. One man told neighbors, before he was arrested and summarily executed, that he was frustrated with his life and wanted revenge on the rich and powerful. Another apparently told police he was upset because his girlfriend had left him.

Los Angeles, U.S.

“Be certain your next child will be the gender you’re hoping for,” promises the Web site of L.A.’s Fertility Institutes. Dr. Jeffrey Steinberg founded the clinic in 1986, just as in-vitro fertilization was taking off.

Today 70 percent of his patients come to select the sex of their baby. Steinberg’s favored method is preimplantation genetic diagnosis, PGD, an add-on to in-vitro fertilization that allows parents to screen embryos before implanting them in the mother. Like amniocentesis and ultrasound before it, PGD was developed to test for defects or a propensity toward certain diseases.

But lab technicians working with eight-celled embryos can also separate XY embryos from XX ones, thus screening for sex-the first nonmedical condition to be turned into a choice. PGD thus attracts Americans who are perfectly capable of having babies the old-fashioned way but are hell-bent on having a child of a certain sex. So determined are they that they’re willing to submit to the diet of hormones necessary to stimulate ovulation, pay a price ranging from $12,000 to $18,000, and live with IVF’s low success rate. Decades after America’s elite introduced sex selection to the developing world, they have taken it up themselves.

High-tech sex selection has its critics. They point to a litany of ethical issues: that the technology is available only to the rich, that it gives parents a degree of control over their offspring they shouldn’t have, that it marks the advent of designer babies. But in surveys of prospective American parents over the past 10 years, 25 to 35 percent say they would use sex selection techniques if they were readily available; presumably that means more affordable and less invasive.

A squat, balding man who exudes a jovial confidence. Dr. Steinberg talks as if he has all the time in the world, peppering his stories with Hollywood gossip. (To wit: The producers of the show CSI once stopped by the clinic to evaluate a sperm cryopreservation tank’s potential as a weapon.) The patient response to his clinic offering sex selection, Steinberg tells me after ushering me into a spacious corner office, has been “crazy.”

The fertility doctors who perform preimplantation sex selection take care to distinguish it from sex-selective abortion. In America, they point out, patriarchy is dead, at least when it comes than the global balance of males to choosing the sex of our children. As late as the 1970s, psychologists and sociologists found that Americans were far more likely to prefer sons to daughters. Not anymore.

National figures are not available, but two of America’s leading clinics—HRC Fertility in Los Angeles and Genetics and IVF Institute in Fairfax, Virginia—independently report that between 75 and 80 percent of their patients want girls. The demand for daughters may explain why at Steinberg’s clinic everything from the entrance wall to the scrubs worn by the laboratory workers are pink.

For the most part, however, Americans don’t talk about gender preference. We say “family balancing,” a term that implies couples have an inherent right to an equal number of boys and girls. (Many patients seeking sex selection via PGD already have a child of the opposite sex.) We talk about “gender disappointment,” a deep grief arising from not getting what we want. The author of the reproductive technology guide Guarantee the Sex of Your Baby explains: “The pain that these mothers feel when they fail to bear a child of the ‘right’ sex is more than just emotional angst. The longing that they hold in their hearts can translate into real physical pain.”

Rhetorical differences aside, “family balancing” is not in fact all that different from what is happening in China and India. In Asia, too, most parents who select for sex do so for the second or third birth. And examining why American parents are set on girls suggests another similarity: Americans who want girls, like Asians who opt for boys, have preconceived notions of how a child of a certain gender will turn out.

Bioethicist Dena S. Davis writes that people who take pains to get a child of a certain sex “don’t want just the right chromosomes and the attendant anatomical characteristics, they want a set of characteristics that go with ‘girlness’ or ‘boyness.’ If parents want a girl badly enough to go to all the trouble of sperm sorting and artificial insemination, they are likely to make it more difficult for the actual child to resist their expectations and follow her own bent.”

When Dr. Sunita Puri surveyed Bay Area couples undergoing PGD for sex selection, most of them white, older, and affluent, 10 out of 12 wanted girls for reasons like “barrettes and pink dresses.”

Some mention that girls do better in school, and on this point the research backs them up: Girls are more likely to perform and less likely to misbehave, while boys have lately become the source of a good deal of cultural anxiety. Others mention more noble goals. They talk about raising strong daughters; women mention having the close relationship they had—or didn’t have—with their own mother.

But regardless of the reason, bioethicists points out, sex selection prioritizes the needs of one generation over another, making having children more about bringing parents satisfaction than about responsibly creating an independent human being.

At stake with preimplantation sex selection is much more than the global balance of males and females, as if that weren’t enough. If you believe in the slippery slope, then sex-selective embryo implantation definitely pushes us a little further down it.

In 2009 Jeffrey Steinberg announced that the clinic would soon offer selection for eye color, hair color, and skin color. The science behind trait selection is still developing, and some later doubted whether he in fact was capable of executing it. Still, Steinberg might have eventually gone through with the service had his advertisement not set off an uproar. The press descended, the Vatican issued a statement criticizing the “obsessive search for the perfect child,” and couples who had used PGD for medical reasons balked, fearing frivolous use of reproductive technology would turn public sentiment against cases like theirs. For the moment, at least, Americans had problems with selecting for physical traits, and Steinberg retreated.

Having children has become more about bringing parents satisfaction than creating independent human beings.

“The timing was off is all,” he tells me. “It was just premature. We were ahead of our time. So we said, ‘OK, fine. We’ll put it on the back burner.’” In the meantime, he says, couples obsessed with blue or green eyes continue to call the office. He keeps their names on a mailing list.

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