Natalie Angier

Menstrual cycle is an alarming clock that cannot be stopped until nature wills it. Moon, month, menses: same word, same world

The image of the nested Russian dolls is used too often. I see it everywhere, particularly in descriptions of scientific mysteries (you open one mystery, you encounter another). But if there were ever an appropriate time to dust off the simile, it’s here, to describe the nested nature of the matriline. Consider, if you will, the ovoid shape of the doll and the compelling unpredictability and fluidity of dynasty. Open the ovoid mother and find the ovoid girl; open the child and the next egg grins up its invitation to crack it. You can never tell a priori how many iterations await you; you hope they continue forever. My daughter, my matryoshka

Yet by menopause, few if any eggs remain in the ovaries. The rest have vanished. The body has reclaimed them

that point a doctor may recommend donor eggs, combining the seeds of a younger woman with the sperm of the older woman’s husband (or lover or male donor) and then implanting the resulting embryo in said senior’s uterus. Using donor eggs can make a woman of forty act like a twenty-five-year-old, reproductively speaking. Who knows why? But it works, oh girl does it work, so well that suddenly you’re no longer in the teens of probability but instead have about a 40 percent chance of giving birth in a single cycle of in vitro maneuvers. That

Male twins share the totality of their maternal X chromosomes, as well as having all the other chromosomes in common, but female twins have a diverging patchwork of maternal and paternal X chromosomes operating in different parts of their bodies.)

Could brain mosaicism also explain why multiple personality disorder (assuming we give it the benefit of the doubt as a genuine psychiatric disorder) so often seems to strike women? Could sufferers indeed be afflicted with internal clashing commandos, mother-speak and father-speak, cacophonous enough to spin off other fragmentary characters? As Teresa Binstock, of the University of Colorado, pointed out to me, nobody can answer such questions yet, because the idea of brain mosaicism is so new “that most neurologists, neuroanatomists, and cognitive neuropsychologists have not yet thought about it.”

was told at the same time that I’d have to commence hormone replacement therapy, take estrogen. I was told that I would never have menstrual cycles, that I would never have children.”

She had what was then called testicular feminization and is now more commonly known as androgen insensitivity syndrome, or AIS. This is a fairly rare condition, affecting about one in 20,000 births. But in its rarity it has something to teach all of us, about how to think about the genetics of sex, and about the correspondence between our chromosomes—the readout from a fetal chromosome screen that will tell you, Ta da!, your baby is a girl or a boy—and our brains and our bodies

Yet if there’s one thing about the pink-blue dichotomy that annoys me, it’s the unidirectional manner in which we sometimes let it slide. It’s fine to dress a girl in blue, but think about pink on a boy. Think hard about subjecting your son to girl clothes. Think about dressing him in a pink T-shirt, and even you, my most rad-chic mother, will hesitate and, in compromise, reach instead for the yellow shirt with the duck on

but if a man puts on a skirt he’d better be ready to pick up a bagpipe and blow