Lindsay Morris / INSTITUTE

At medical school, in the mid-’90s, my pediatric training took place in a Victorian hospital in Edinburgh called the “Sick Kids.” But it began before birth, so to speak, at the modern maternity unit a short stroll away across a park lined with elm trees. It was there in Edinburgh’s Royal Infirmary that I was obliged to deliver 20 babies and learned about the many perils that attend the first few minutes of life. When I’d been signed off as competent to assist births, the next stage in training followed the newborn babies into an adjoining neonatal unit.

The babies we admitted were often mortally ill and critically underweight, but one day there was an unusual admission: a perfectly healthy nine-pound newborn. In the moments after birth, when the newborn’s parents had cried out to ask if it was a boy or a girl, the midwife had gasped, “I don’t know!” The baby had ambiguous genitalia, a small penis as well as a vagina. He or she was robust and feeding well—it was quickly established that the baby suffered no metabolic or hormonal problems causing the ambiguity. The only reason to stay in the hospital was to figure out whether she really was a he, or vice versa. The importance the medics placed on the distinction was implicit even in the name bands we wrapped around the babies’ wrists. These were usually color-coded pink or blue, but the new baby was given one of white. The parents were anxious and bewildered, and only became more so when the attending neonatologist began to speak of blood tests, scans, gonadal biopsies.

Later that day I walked back through those boulevards of elms to the library at the Sick Kids. “Ambiguity of the external genitalia at the time of birth causes great distress,” I read. “Sensitive explanation is vital.” It was estimated that one in 2,000 babies manifest some degree of genital ambiguity, and as regards the tests: “Complete diagnostic evaluation requires special expertise as it has to consider the long-term functional role of the individual as well as the precise gender.” The book went on to explain that intersex babies could turn out to be genetic females (with two X chromosomes), whose clitorises had swelled to the size of small penises because of a hormonal condition generating unusually high levels of androgens (testosterone-like hormones) while still in the womb. But there were genetic males (with an X and a Y chromosome), whose developing genitalia had proven partially insensitive to testosterone, or who hadn’t been able to generate adequate amounts of the hormone to physically differentiate. As human beings, our default form is female—if the bodies of male babies don’t sense androgens in their blood, they develop short, blind-ended vaginas. These two broad groups described the vast majority of babies with ambiguous genitalia.

There was a third category in the textbook: “true hermaphrodites,” babies born with both testicular and ovarian tissue, and small penises as well as wombs and vaginas. Highly improbable events had to coincide for this to happen, and there were several ways it could come about. One is that a “male” sperm carrying a single “Y” chromosome, and a “female” sperm carrying a single “X” chromosome, can fertilize an egg that has just divided, then those fertilized eggs fuse together. The bodily tissues of these “true hermaphrodites” are often a tessellated patchwork of male and female cells, and are known in medical jargon as “mosaics.” Mosaicism has been known since at least the 1930s, but it wasn’t until the late ’50s that it was realized this phenomenon could lead to hermaphroditism.

The assumption implicit in my training was that, as regards gender, we are born neutral—all of our gender-typical behaviors, whether male or female, are socialized. The textbook also said in clear but insensitive style: “A genetic male with functioning testes but feminized external genitalia is better reared as a girl.” I wondered how they could be so sure.