The most mysterious cells in our bodies don’t belong to us
Katherine J. Wu writes: Some 24 years ago, Diana Bianchi peered into a microscope at a piece of human thyroid and saw something that instantly gave her goosebumps. The sample had come from a woman who was chromosomally XX. But through the lens, Bianchi saw the unmistakable glimmer of Y chromosomes—dozens and dozens of them. “Clearly,” Bianchi told me, “part of her thyroid was entirely male.” The reason, Bianchi suspected, was pregnancy. Years ago, the patient had carried a male…