An Awkward Evolutionary Theory for One of Pregnancy’s Biggest Complications

In the early 1990s, while studying preeclampsia in Guadeloupe, Pierre-Yves Robillard hit upon a realization that seemed to shake the foundations of his field. Preeclampsia, a pregnancy complication that causes some 500,000 fetal deaths and 70,000 maternal deaths around the world each year, had for decades been regarded as a condition most common among new mothers, whose bodies were mounting an inappropriate attack on a first baby. But Robillard, now a neonatologist and epidemiologist at Centre Hospitalier Universitaire de La Réunion, on Réunion Island in the Indian Ocean, kept seeing the condition crop up during second, third, or fourth pregnancies—a pattern that a few other studies had documented, but had yet to fully explain. Then, Robillard noticed something else. “These women had changed the father,” he told me. The catalyst in these cases of preeclampsia, he eventually surmised, wasn’t the newness of pregnancy. It was the newness of paternal genetic material that, maybe, the mother hadn’t had enough exposure to before.

Robillard’s idea was unconventional not only because it challenged the dogma of the time, but because it implied certain evolutionary consequences. Preeclampsia appears to) to humans, and may have arisen as a by-product of the particularly aggressive ways in which our fetuses pillage their mother’s body for resources. So, Robillard and his colleagues posited, maybe the dangers it poses then pressured humans into developing a bizarre trait: being rather inefficient at conceiving offspring. Maybe, if humans aren’t terribly fertile, they need to have a lot of sex; maybe having a lot of sex repeatedly exposes a mother to her partner’s semen, inuring her to the molecular makeup of future offspring. If preeclampsia is a kind of , then perhaps unprotected sex is the world’s most unconventional allergy shot.