A Woman's Best Defense

By Anastasia Toufexis

When I first learned about menstruation at age seven," says Margie Profet, "I couldn't believe it! Then when we watched these films when I was 10 or 11 -- remember those cartoons that showed the ovaries and the Fallopian tubes? -- I thought, This is really bizarre. And when they said, 'Well, the body gets rid of the uterine lining because it has nothing to do,' I thought that didn't make sense. It bugged me."

A quarter-century later, Profet, 35, thinks she has finally made sense of it all, and in a startling turnaround, it is her views that are bugging the experts. Writing in the current issue of the respected Quarterly Review of Biology, the evolutionary biologist from the University of California, Berkeley, has proposed a radical theory of menstruation that not only challenges accepted wisdom but stands it on its head. According to Profet, a woman's flow is not some incidental event in the reproductive process or just a sign of failed fertility. Instead, it is a mechanism that protects fertility by preventing sperm-borne bacteria from infecting the womb.

Profet argues that by unquestioningly accepting the traditional view of menstruation, physicians have unwittingly sabotaged a woman's natural defenses with inappropriate medical treatments in cases of uterine infection. "Imagine consulting a cardiologist who didn't understand that the function of the heart was to pump blood?" asks the maverick scientist. "How could he treat you? That was a fundamental question in the 1600s. The same is true today for women's reproductive systems."

Profet's many admirers in academia quickly lauded the new theory. "She has a brilliant hypothesis and substantial evidence. I'm curious to see if it holds up," says Dr. Randolph Nesse, a psychiatry professor at the University of Michigan. "It's the only serious contender for a plausible evolutionary explanation of menstruation," declares George Williams, an editor at the Quarterly Review of Biology, which is published by the University of Chicago Press. "It is extremely unlikely that her theory is seriously wrong. Her arguments are quite convincing."

Not to all M.D.s, however, who are befuddled by the attention Profet's work is getting, including a prominent story last week in the New York Times. That largely uncritical article included praise for Profet from anthropologist Donald Symonds of the University of California at Santa Barbara -- without mentioning that he is a close friend of the biologist's.

Medical experts complain that the glowing press coverage is not justified because Profet got her physiological facts wrong. "While Profet has done a lot of library work, she's not comfortable with all aspects of reproductive biology," says John Rasweiler, associate professor of reproductive biology at New York Hospital-Cornell Medical Center. "When you focus on some of her errors, many things seem to fall apart." Errors? "Every gynecologist knows the incidence of pelvic infections increases, not decreases, after the menstrual period," contends Dr. Charles Debrovner, associate professor of obstetrics and gynecology at New York University School of Medicine. "In fact, menstruation makes women more susceptible. Menstrual blood itself may even act as a vehicle for transporting infection." Counters Profet: "Saying uterine bleeding causes infections is like saying a fireman causes a fire."

The biologist concedes that she did not run her paper by practicing doctors. "Gynecologists have no training or background in analyzing evolutionary adaptations," she says. "This paper is not primarily a clinical work. The principal part of it is zoological."

Profet arrived at her controversial theory by posing an age-old question: Why do women menstruate at all? As a means of disposing of unfertilized eggs and a plumped-up uterine lining, a monthly flow seems peculiarly wasteful. Women shed a great deal of blood and tissue, as well as valuable nutrients, particularly iron. "If menstruation were both costly and functionless," reasons Profet, "natural selection surely would have eliminated it long ago." Its persistence suggests that it offers some advantage.

What that advantage is, says Profet, came to her five years ago when she was awakened from a sound sleep one night by a neighbor's cat. "I'm in the middle of a dream," she recalls. "And I'm seeing those cartoons about menstruation, but now I'm seeing these black triangles in the endometrial lining, and I go, 'Whoa, those triangles are pathogens.' "

That dream evolved, after plenty of thought and research, into a full-blown thesis. Profet's reasoning begins with the observation that potentially harmful bacteria can catch a ride into the womb and Fallopian tubes by attaching themselves to sperm. The microbes can come from the male or get picked up in the vagina during sex. Menstruation eliminates the threatening intruders in two ways: the sloughed-off uterine lining carries the microbes off, and the blood itself is rich in immune cells ready to gobble up any alien invaders.

But what about women who are pregnant or have gone through menopause? Since they don't menstruate, how do they ward off bacteria? Profet notes that in the first six months of pregnancy and in some cases after menopause, the cervical entryway to the uterus is covered by a mucous plug. The mucus makes it hard for sperm -- and their nasty hitchhikers -- to enter the uterus, and thus reduces the need for a monthly blood flow. Profet suspects that doctors may be making a serious mistake by routinely regarding irregular bleeding as an endocrine problem to be stopped with hormone therapy. "If there's an onset of bleeding, you should suspect infection," she maintains. Halting the flow with drugs could be counterproductive.

To back her theory, Profet relies on electron-microscopy studies that show bacteria attached to the heads and tails of wriggling sperm. She also cites the existence of spiral-shaped arteries in the uterus. These specialized blood vessels constrict and dilate in a sequence timed to induce menstruation. And, she claims, the blood that washes over the uterine walls differs from blood that circulates throughout the rest of the body. Menstrual blood lacks ingredients that cause clotting and is rich in special immune cells called macrophages. Even so, says Debrovner, "there is no reason to believe that blood, no matter what it contains, is going to wash away infection. It just doesn't work like that. It's not like blood gushes by an area and cleans it up."

Another debatable point is Profet's claim that menstruation is widespread in mammals. She acknowledges that this part of her theory is speculative, but she predicts she will eventually be proved right. "You can't say these animals don't menstruate just because you can't see it," she explains. "You have to dissect them to find it." Rasweiler agrees, but so far, he insists, there is little evidence that any more than a handful of species -- including primates, bats and elephant shrews -- menstruate. "If other species don't, that raises % the question of how they rid themselves of pathogens," says Rasweiler.

Taking a page from Profet's own method, some critics challenge her by citing history. Today's women can have 400 menstrual periods over a lifetime, but earlier women probably had only a few dozen. Without birth control, they spent most of their reproductive lives pregnant or nursing. "Women were never meant to menstruate on an ongoing basis," says Dr. David Olive, the head of endocrinology at Yale University medical school. If menstruation is supposed to be a rare phenomenon, then how can it be a primary defense against infection? In fact, it may turn out that menstruation is the most efficient way to start the reproductive cycle again, if pregnancy does not occur. Contends Rasweiler: "Menstruation is a marvelous way of recycling the uterus."

The debate Profet has started may not be easily resolved. If nothing else, though, she has provided a fresh way of looking at an old mystery. It's not enough, she says, to know what happens during menstruation. The more intriguing questions: Why does it happen, and how did it help humans survive to be among evolution's winners?