"Any behavior you can think of," says Mark Kristal, a professor of psychology from the State University of New York at Buffalo, "somebody, somewhere, has done it." That includes placenta eating, though Kristal is pretty sure that it has never been a common practice in any extant human culture. But while I was working on a recent piece for Slate about patients taking home keepsakes from surgery, I kept coming across stories about the practice, known as placentophagy (Wikipedia).

Part the reason for the interest is the gross-out factor. The placenta is "one of the ugliest things to ever come out of the human body," says Kristal, the world's leading expert on the subject. "And not only is it unappetizing, but it's also reminiscent of cannibalism." Another factor is that the recent practitioners of placentophagy have mainly been Americans. During the 1960s and '70s, there were a few reports of the practice on hippie communes. Today, most of the adherents of placentophagy come from New Age groups who believe that ingesting the placenta could help stave off postpartum depression.

Weirdly, they might be on to something. Since his paper in Neuroscience & Biohehavioral Reviews over 25 years ago, Kristal has focused on the reasons behind placentophagy, a practice that is prevalent in many animals. Many of the females from these species seem desperate to ingest it, which led Kristal to believe they were getting a benefit above and beyond nutrition.

"In rats, it's easier to take pups away from [new mothers] than the placentas," he says. In fact, he notes, the rats often get sick if they don't ingest afterbirth. Kristal's studies have shown that amniotic fluid contains substances that dull pain by boosting the body's internal opioids. Humans used to receive some of this benefit, too, Kristal believes, though not necessarily from placentophagy. Instead, mothers used to kiss and lick their babies while the latter were still covered in amniotic fluid. Today, the sterile environment of hospitals means that babies are often washed and wrapped before being handed over to mom.

So while it may not be the cure for postpartum depression, placentophagy may offer some help in the postlabor recovery process. That's why Kristal is creating a medication by synthesizing the relevant placental chemicals.

Interestingly, though, he thinks that current versions of human placentophagy aren't useful in this regard. "They cook it," he says. "And there's a lot of evidence that [the useful organic materials] don't survive this. For them, it's more of a social bonding, placebo-type effect."