Why Do Women Menstruate?

Science News, April 12, 1997 by John Travis

This, says Ellison, means that the endometrial cells are committed to their fates before an embryo arrives and that they have a limited life span. That's why there's only a day or two during which embryos can successfully implant, he says. "The endometrium isn't good after that. You can't save it for later," contends Ellison. Consequently, women shed the outdated lining via menstruation each time they do not become pregnant.

Colin A. Finn, a researcher at the University of Liverpool Veterinary Field Station in Neston, England, independently offers a similar line of reasoning in an article on menstruation's evolution that appears in the December 1996 EUROPEAN JOURNAL OF OBSTETRICS AND GYNECOLOGY AND REPRODUCTIVE BIOLOGY.

Strassmann responds that the arguments of Ellison and Finn seem flawed. She says that anatomists have established that the cycle of endometrial growth and regression is found in all mammals, even those that lack invasive implantation.

The debate over menstruation is certainly far from over. Perhaps the key point about this academic dispute, however, is that it is occurring at all.

Hill says, "I think the most important contribution Margie Profet made, which will stand regardless of the utility of her idea, is bringing to light really clearly that we have to start thinking about the functional significance of things. We can't just take something like menstruation as a given."