Hypothesis on evolution of PMS attracts hostility

Premenstrual syndrome, or PMS, can be a miserable experience. Women report over 200 symptoms in the days before menstruation occurs. The complaints run the gamut from irritable mood to bloating. PMS can be so slight you don’t even notice, or it can be so severe it has its own category — premenstrual dysphoric disorder. But to some, PMS is just a punchline, a joke featured in pop culture from Buffy the Vampire Slayer to Saturday Night Live.

Michael Gillings, who studies molecular evolution at Macquarie University in Sydney, thinks that PMS could have a purpose. In a perspective piece published August 11 in Evolutionary Adaptations, Gillings proposes that PMS confers an evolutionary advantage, increasing the likelihood that a woman will leave an infertile mate. He hopes that his idea could lead to more research and less stigma about the condition. But while his hypothesis certainly sparked a lot of discussion, whether it is likely, or even necessary, is in doubt.

Gillings first began to think about PMS when he found out that premenstrual dysphoric disorder was being added to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders. “I started to think that we have a normal distribution of PMS responses, where some people don’t get any symptoms, the majority gets mild symptoms, and some get severe symptoms,” he explains. Including PMDD in DSM-5 made a statement, he says, that “we were going to take one end of this normal curve, the extreme far right end, and we were going to draw a line and say, those people there have a disease we’re going to label in our book. But if 80 percent of women get some kind of premenstrual symptoms, then it’s normal. And I wondered, if it’s so normal, what could be the reason for it?”

Gillings began to read studies on PMS, fertility and genetics. He was especially inspired by work from Beverly Strassman, an anthropologist who wrote on the hunter-gatherer Dogon tribe in Mali. Dogon women go to a special hut during menstruation. But because they spend a large amount of their time pregnant or nursing, they don’t menstruate often. “She found the median number of menstrual cycles for the women in this tribe was two per year,” says Gillings. “So I thought, if you were a woman in that society, and you were bonded to an infertile male, you would be in the menstrual hut every month, you’d have a very different experience.”

Gillings hypothesized that when a woman had an infertile partner and menstruated monthly, the “hostility” associated with PMS could be evolutionarily advantageous: Women with PMS might direct anger at their partners, increasing the likelihood that the partnership will dissolve and leaving the woman free to find a better — and presumably more fertile — mate.

“Any behavior or any trait, any genetic tweaking that even raises the chance marginally that you will reproduce, is hugely advantageous,” he says. To support his hypothesis, he cites studies that associate certain genes with PMS symptoms. He also cites papers showing that women with PMS suffer from more marital dissatisfaction, and that women with PMS might be more impulsive, making the more inclined to jump relationships.

But the perspective is, as yet, only a hypothesis. And other scientists are not so thrilled with this PMS “just-so” story.

Mark Elgar, who studies evolutionary biology at the University of Melbourne in Australia, views the hypothesis as “rather fanciful.” He says that while symptoms of PMS might indeed be heritable, there’s no evidence that PMS is directly controlled by specific genes. But most importantly, he says, there’s no association between PMS symptoms and how many children a woman has. “In other words,” he explains, “there doesn’t seem to be a very compelling reason to construct an evolutionary explanation of PMS in the first place.”

Jane Ussher, a women’s health psychologist at the University of Western Sydney in Australia, says while she agrees PMS can “lead to or exacerbate relationship tension,” she does not see how this might drive away infertile males. “Women are fertile before the premenstrual phase of the cycle,” Ussher explains, “so any function of PMS in terms of repelling males would have no impact on fertility.” She notes that while PMS is associated with relationship problems, it may be more of a symptom of the problem than a cause. “Women who are unhappy premenstrually usually have something else to be unhappy about,” she explains. They may feel pressure from life responsibilities, on the job or from other issues in the relationship.

Susan Brown, an evolutionary psychologist at the University of Hawaii at Hilo, whose 2011 paper on women’s sexuality and the menstrual cycle was cited in Gillings’ piece, also says she did not find his arguments compelling. “The contention that PMS sufferers direct most of their ‘hostile’ behavior at their partners is also questionable,” she says. Further, some women with PMS do have increases in libido, but, Brown explains, “this does not imply, as Gillings does, that this sexual behavior is with non-partners. In fact, because this is the time of the cycle where conception is extremely unlikely, we feel that it is used to heighten rather than decrease pair bonding.”

Gillings emphasizes that his proposal is just a hypothesis, one that has not yet been tested.  “I’m not in the business of doing this kind of research. I can’t test any of the predictions. But I hope it will raise discussion about PMS in the scientific community and in the general public.” In particular, Gillings wants to decrease the stigma surrounding PMS. “At the moment it’s a cliché,” he notes. “It’s demeaning in a way, it’s a standard kind of joke and I don’t think it’s funny.”

But Elgar disagrees that the new hypothesis will decrease stigma, stating that “it will add fuel to the negative stereotype that women are emotional slaves to their hormones.” Indeed, some of the coverage has reacted to the study with comments about “crazy cave ladies,” which isn’t exactly a tolerant view.

The idea that PMS could make a woman leave an infertile coupling is one that could be attacked with scientific rigor.  Although the hypothesis might offer an explanation, there are many other hypotheses that could contribute, including surrounding stressors and cultural norms. “We don’t need to look for an evolutionary explanation for PMS,” Ussher says. “We simply need to look at the social context of women’s lives, and the gendered inequities in their relationships.” Ultimately, the explanation for distress from PMS might be from many other sources than just her genes.