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An unproductive story of reproductive success and PMS

Apparently, premenstrual syndrome could save ancestral women from evolutionarily disastrous reproductive failure by driving away infertile partners. Thomas Hawk/Flickr, CC BY-NC

It’s been a mixed week for women and their hormones.

When Maryam Mirzakhani became the first woman to win the prestigious Fields Medal for mathematics, a Cambridge mathematician suggested it would “put to bed many myths about women and mathematics”, one of which is the idea that females are not exposed to enough prenatal testosterone to excel in the field.

At the same time, other hormone-related myths were given fresh life by a new evolutionary story claiming to have uncovered the reason why women become “unbearable to live with” once a month, as one news report put it.

Michael Gillings, a population geneticist at Macquarie University, suggests in an article published in the journal Evolutionary Applications that premenstrual syndrome (PMS) evolved because it enabled women to repel men who failed to make them pregnant.

The fantastic past

In our ancestral past, the story goes, women would have had many fewer menstrual cycles due to greater numbers of pregnancies and extended breastfeeding. Being partnered with an infertile man would therefore have gone hand-in-hand with regular menstruation.

Premenstrual syndrome could save ancestral women from evolutionarily disastrous reproductive failure. Having successfully driven off an infertile partner by means of bad-temperedness administered on a monthly schedule, women would be at liberty to seek out a fresh victim.

A well-rehearsed criticism of this kind of fanciful evolutionary speculation is that many aspects of contemporary human conditions are not adaptations; they are not “for” anything.

Contrary to popular “paleofantasy”, which holds that we embody perfected design for a long-gone era, evolutionary change is a compromised, continuously jerry-rigged process that has to always act within the constraints of what’s already there. This means many of our characteristics, including some that are typical or universal, have no evolutionary purpose.

Often, speculating about what adaptive purpose is served by some feature of a pocket of contemporary life is to board the express train to Storyland.

But Gillings argues that the high frequency of the currently “maladaptive” condition of PMS, with “often … significant personal, social and economic costs”, points to an offsetting adaptive benefit from the past.

Not as bad as all that

However, the picture painted of the incapacitating effect on modern women of their reproductive system is far too bleak.

Only a small percentage of women (estimates have ranged from as low as 1.3% to around the 5% to 8% mark) have premenstrual symptoms that are genuinely debilitating and merit a diagnosis of premenstrual dysphoric disorder.

The picture painted of the incapacitating effect on modern women of their reproductive system is far too bleak. TipsTimesAdmin/Flickr, CC BY

And while 80% of women do indeed report experiencing what Gillings describes as PMS, what this actually means is that they’ve experienced potentially as little as one of a long and generic checklist of “symptoms”, such as abdominal bloating, tension, and poor sleep.

What’s more, a careful and comprehensive 2012 review of studies on mood and the menstrual cycle:

failed to provide clear evidence in support of the existence of a specific premenstrual negative mood syndrome in the general population.

Of the 47 studies identified as of being of adequate quality, only 15% found the expected link between negative mood and the premenstrual phase.

And when, in a different study, researchers looked directly for associations between moods and the ovarian steroid hormones (estrogen and progesterone) assumed to drive them, they mostly failed to find any links.

While there were a few significant correlations here and there, mood and hormones were mostly unrelated. In line with the review study, menstrual cycle phase was also largely unrelated to mood.

What did predict mood well, by contrast, was perceived stress and physical health, leading the researchers to conclude:

Taken together, our findings suggest that natural fluctuations of ovarian hormones do not contribute significantly to variations in the daily moods of healthy women.

Fertility fantasy

Another major derailment for Gillings’ story comes from closer examination of the implicit assumption that it’s very easy for a man to impregnate a fertile woman.

Indeed, the premise that a man can father vast crops of children by spreading his seed widely is treated as an axiom of evolutionary psychology, and serves as the foundation of claims about evolved sex differences in mating preferences.

But there are many reasons why conception might fail to take place following one single sexual act, even if both parties are fertile. It can take several months for a typical modern couple to achieve an intended pregnancy.

For women to have evolved relationship-curdling tendencies in such circumstances would hardly seem to be adaptive.

Remarkably, Gillings suggests the idea that women are maladaptively driven to corrode relationships with their irritability and mood swings will help to “depathologise” PMS.

That seems rather optimistic; attributing behaviour to internal, biological factors doesn’t neccessarily have destigmatising effects. It seems at least as likely that Gillings’ evolutionary story will instead reinforce and legitimate negative stereotypes of women as irrationally emotional.

And that should irritate everyone, no matter what day of the month it is.

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