Ovulatory overtures: do women’s preferences shift with their fertility cycle?

About a month ago, I stumbled across a paper that left me with the warm reinforcing glow that comes with being right. The rather artificial experiment played female subjects two pieces of music varying in complexity, and then asked each subject which of the male composers they preferred sexually.

All the subjects had to go on was the piece of music. Women at the fertile peak of their menstrual cycles preferred the composer of the more complex tune for a short-term thing. At other times, or if asked to rate the composers for suitability as a long-term mate, subjects showed no preference.

Does the attractiveness of musicians depend on the fertility of the beholder? Source: True British Metal/Flickr
Does the attractiveness of musicians depend on the fertility of the beholder?
Source: True British Metal/Flickr

My vindication was the paper’s support for the idea that music-making ability is preferred by those seeking mates. Such a preference is one possible way in which our ability to make and to appreciate music might have evolved, a position I happen to think is right. The paper’s test is pretty simplistic, but the addition of a new line of evidence gives the idea of sexually selected musicality another strand of support.

As a scientist I should be wary of my own reaction to the evidence. It is all too easy to count the “hits” that confirm one’s world view and ignore the “misses” that contradict it. Such confirmation biases build distorted and, left uncorrected, incorrect beliefs. They constitute the prime ingredient in religious faith and ideological zeal of all stripes. And science, done properly, is the only known antidote.

But what happens when science probes the most ideologically polarising questions themselves? Well, a very interesting case is unfolding right now concerning the science of how women’s fertility cycles shape their mating preferences.

Shifting cycles

The musical complexity paper builds on an idea in evolutionary psychology that women’s sexual preferences and desire “shift” at the time they are most likely to conceive, favouring men of superior genetic quality over the kinds of men likely to make good long-term partners and co-parents.

This “ovulatory shift” idea contains many moving parts, each of which has at least some support.

The best man to raise a child with is not necessarily the best available gene-donor. So women might profit, in evolutionary terms, from pairing up with a nice guy – hard-working and safe to be around – while discreetly also mating with a different, highly masculine, ridiculously good-looking paragon of genetic endowment.

Such liaisons come with risks, however, including being abandoned – or worse – by the cuckolded long-term partner. So it’s only worth “gene shopping” when you stand a good chance of conceiving.

The very idea makes many people squirm. But not everybody is squirming for the same reasons.

Mating preferences, and even how revealingly a person dresses may be influenced by where in her ovulatory cycle a woman is. This isn’t a popular idea with some ideologies and religions. Nathan Rupert/Flickr
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Social conservatives and religious traditionalists are often confronted by the sexual freedom and agency implicit to ideas like ovulatory shifts. It’s just too much to accept that some “good” women – wives even! – might play the odd away game for biologically rational reasons. Much easier to wash all that complicated evolutionary nuance away with a cleansing deluge of scriptural literalism.

Interestingly, evolutionary accounts of human behaviour come under equally heavy fire from the opposite end of the political spectrum, where biology can play no role in understanding society.

Cultural creationists, most of whom show no evidence of ever having attempted to understand evolution, prefer to flail at “biological determinism”. In their cartoon world, those wearing the white hats shoot from the hip at oppressive biological stereotypes, secure in the conviction that everything interesting about human behaviour arises as the results of learning, culture and social construction.

But here in the 21st century, serious academic research should be above the ancient laziness of pitting nature and nurture as competing alternative explanations. Unfortunately that habit remains too hard for some authors to break.

I’m certainly not claiming we shouldn’t be very careful about biological explanations. When it comes to women’s hormonal cycles, history shows the merit of treating biological claims sceptically. One can draw a straight line from Classical Greek ideas that the uterus wandered about the body causing all sorts of ailments to the popular diagnosis of “hysteria” for almost any psychological and many somatic complaints in 19th century Europe and America. The very word “hysteria” derives, after all, from the Ancient Greek for uterus.

Biological ideas are still widely used to confine and oppress women. Consider the recent controversial review of studies concerning mood and the menstrual cycle. Here at The Conversation, Jane Usher took that paper as reason to dismiss premenstrual moodiness as a myth. Jayashri Kulkarni responded that PMS is real and denying its existence harms women.

What about the evidence?

Whatever our political predispositions, surely we should be led by the evidence in deciding whether ovulatory shifts are real?

An impressive number of studies show that women in the “fertile phase” of their cycle express different preferences from those in less fertile phases and women on hormonal contraception. In particular, preferences for typically masculine male faces, behaviour, personality traits and health all peak in the fertile phase. And at peak fertility, women in long-term relationships more often report attraction to men other than their partners, and weaker attraction to their partners. Especially when those partners aren’t paragons of masculine attractiveness.

Many other studies, however, have found no evidence of ovulatory shifts. And who knows how many unpublished studies languish in researchers’ file drawers? This is just the job for a meta-analysis, the suite of statistical techniques for sifting a body of published results to extract the overall level of support for a hypothesis.

Recent months have seen not one, but two meta-analyses of the subject. One, led by Wendy Wood at the University of Southern California, concentrated only on preferences for high testosterone, masculine, dominant or highly symmetric men. Their meta-analysis of 45 published and 13 unpublished studies found no overall support for shifting preferences across the menstrual sample.

Across town at UCLA, Kelly Gildersleeve, Martie Haselton and Melissa Fales meta-analysed 134 effects from 38 published and 12 unpublished studies. In contrast with the USC paper, the UCLA team found robust cycle shifts when women were asked to assess men as short-term mates, but not when assessing long-term partners.

Two meta-analyses, published within months of each other, asking more-or-less the same questions, but getting different answers. That’s not how science – and meta-analysis in particular – is meant to work!

But, strangely, it’s not an unusual turn, particularly when the research concerns polarising issues. My good friend Michael Kasumovic pointed me to the following meta-analytic back-and-forth on the links between videogames and violence. His precis:

2001: Video games cause aggression.

2007: No, no, it’s a publication bias.

2007: See, it really is a publication bias.

2010: No! They really cause aggression!

2014: Actually, violent games increase aggression, and pro-social games increase prosocial behaviour …

… and so on it rolls. Meta-analyses of existing data do not provide the hoped-for panacea, much less change minds, particularly when the issues at stake are ideologically infused. At least not instantaneously.

This ovulatory shift story is far from done. The differences in sampling and analytic approaches between the two teams are still shaking out. I’ve been in touch with both groups and will shortly write another column trying to get to the bottom of how they reached such different conclusions. Before I do so, I’m waiting for one more paper to hit the presses, in order to be sure both teams have similar opportunities to present their cases.

Look who’s celebrating

For now, it remains worth asking what’s at stake. This rather intriguing business represents just the latest squall in the tempestuous relationship between the biological and social sciences. And it’s in danger of descending into rude tribalism.

Claims about ovulatory shifts are seen in some quarters as just another example of women’s cyclical biology being used to deny their agency and independence.
Wood’s meta-analysis invigorated anti-biology defenders of the faith. Consider Amanda Hess, whose Slate column often oozes thoughtful analysis. Whenever Hess strays near evolution, however, she becomes unwilling to weigh complex ideas on their merits. Her column on the Wood et al paper ran with a weak “patriarchal scientists don’t understand female bodies or the ineffability of culture” trope.

Her own biases confirmed, and making no mention of the earlier-published Gildersleeve meta-analysis, Hess rejoices that “a woman’s cultural conditioning is even more powerful than progesterone”. To pilfer an expression as hackneyed as Hess’ argument, 1975 called, and they want their false nature-nurture dichotomy back.

This kind of buy-in to outmoded all-biology-equals-determinism thinking seems so at odds with the way evolutionary psychologists and biologists really view behaviour. But look at what the journalists were working with. The press release USC put out quotes Wood:

A complete model of human reproduction needs to acknowledge women’s impressive capacity to regulate their own behavior and not fall into the trap of biological determinism […] Regardless of what might have been normative in ancestral history, with the advent of cultural roles and complex group living, women showed the capacity to tailor their reproductive activities to a variety of social roles.

Resistance to the notion of ovulatory shifts, then, springs from the fear that if hormones influence behaviour, then that robs women of their capacity to act independently and in their own interests. Claire Lehmann provides a scathing rebuttal of this argument, skewering wilful cultural creationist ignorance of how biology really shapes behaviour.

What fascinates me about this issue is how the anti-biology crowd are jumping at shadows. If evolutionary psychology conferences are secret gatherings of patriarchs out to perpetuate the status quo, then their cover is outstanding. What I see is a vibrant field concerned with the subtle ways in which women and men act in their own evolved interests.

Ovulatory shift research in particular, conducted by far more women than men, uncovers ever more intriguing nuances to women’s motives, actions and how they interact with deliberate and equally strategic behavioural self-regulation. Those most interested in gender equity and the liberation of female sexuality from that other – original – kind of creationism might well benefit by paying close attention to the field of evolutionary psychology.

Science is always done by people, and we all bring our own personal and scientific preferences and biases to the enterprise. What we do with those influences in the face of the evidence is what really matters.

The Conversation

Rob Brooks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

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Fred dives, Neymar scores, Brazil wins! Straight out of the textbook

The soccer World Cup (yes, I persist in calling it “soccer”) is the one time in every four years I pay any sustained attention to the round-ball game. There is so much to love about the world’s most popular sport, played by its best players, with fanatical but mostly benign national supporters.

And yet by tournaments’ end I cannot bear to watch another dive, any more theatrical writhing on the ground or another posse of 20-something millionaires heatedly admonishing an official. Perhaps it’s something in the water at my place or a consequence of being thrashed too frequently in high school, but I prefer the stoic deference to authority of rugby union, in which backchatting the referee automatically moves the penalty 10m closer to your goal line.

So, with all the bright-eyed hope in the world game, I rose this morning at six to watch Brazil’s inevitable dismantling of Croatia. But Croatia’s Portuguese interpreter clearly couldn’t understand the memo, written as it was in Português do Brasil. Unaware they were supposed to be dismantled, they had the temerity to go ahead in the 11th minute.

A cracking contest, then, made even when Neymar slipped one just inside the Croatian post in the 29th minute. Very little remonstrating, some robust challenges but not too much play-acting, and very few dives. Until the 71st minute.

This is why soccer players dive. “Scientifically proven” as they say in pseudoscientific advertisements for fast-moving consumer goods. In this case, Fred’s dive fits perfectly with a scientific analysis of soccer diving by Gwendolyn David in 2011 and a team of collaborators at the University of Queensland.

In order to understand the dynamics of who dives and when, David viewed 2,800 falls in 60 matches of soccer across 10 professional leagues. David’s PhD supervisor and collaborator on the paper, Robbie Wilson, and Amanda Niehaus wrote about the paper’s findings and implications for The Conversation when the paper was published. As they put it:

It turns out that diving is more common when there’s more to gain by it: in the offensive half of the field – specifically, in or near the penalty box – and when scores between the teams are tied.

That’s exactly what happened this morning. Fred dived in a part of the field where he had everything to gain and almost nothing to lose. And it isn’t just Croatian supporters who thought the decision to award a penalty – the penalty that broke the tie – diminished an exciting game of football.

I’ll probably get up most mornings to watch the games, but I’d rather see referees take a harsher line on the theatrics. Like those zero-tolerance rugby referees, I’m pretty sure a few more yellow cards would tone down the histrionics and improve the overall spectacle. In fact David’s analysis shows that in leagues where refs are tough on diving, players do it less often.

My daughter was born the night John Aloisi scored that goal to put Australia through to compete in Germany 2006. And all Australian supporters know where that campaign ended up. Two words: Fabio Grosso.

This article was originally published on The Conversation.
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What Makes Us Human?

What separates humans from other animals, including our closest relatives?

Thomas Henry Huxley was a dynamic chalk-and-talk lecturer and a fabulous anatomist. Here he is lecturing on the anatomy of the gorilla skull.
Thomas Henry Huxley was a dynamic chalk-and-talk lecturer and a fabulous anatomist. Here he is lecturing on the anatomy of the gorilla skull.

It’s one of those big questions perennially posed by the evo-curious public. But until recently I seldom gave it much thought. Mostly because the answers tend to get hung up on one trait that differs from our closest great ape relatives: our upright stance, the shape of our toes, the size of our brains.

Millions of years of separate evolution has, of course, resulted in considerable divergence in all manner of traits. It makes no sense to elevate one particular one to some kind of special status – the one thing that makes humans … human.

Questions about what separates us from other animals also carry some unfortunate baggage. The belief that there is something inherently special about humans and the way we arose is more suited to creation mythologies and religious doctrine than to a scientific, testable view of the world. The notion of special creation, and those perversions of evolutionary thinking that defend humans as exceptions, tend to come pre-fitted with taxonomic chauvinism of the following sort:

Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.

Victorian clash of minds

The shard of evolutionary thought that most gets under the skin of religion is the notion that humans are not created special, are not made in any divine image. Darwin’s contemporary, the great anatomist Richard Owen, fiercely defended humanity’s paragon status and the Victorian English status quo from transmutationalism (as evolutionary thought was then known) and the bestialisation of man.

When the first pelts and skulls of a large newly discovered “indescribably fierce” African ape (the gorilla) sensationalised 1850’s London, they piqued the curiosity of a working class then challenging ideas of human uniqueness and a divine social order. Owen lectured the British Association in 1854 that human brains bore special structures – such as the hippocampus minor – lacking in apes. Here, Owen claimed, lay the evidence for human uniqueness.

A young Thomas Henry Huxley located the gorilla’s hippocampus minor (remember they were working with skulls) in March 1858 (months before the Darwin-Wallace paper on natural selection), showing himself the better anatomist. More important, Huxley’s interpretation that chimps, gorillas and humans are at least as similar to one another as any is to baboons – now common knowledge – devastated Owen’s claims to human uniqueness.

One by one, all claims to human uniqueness have similarly fallen aside. For example, in 1960 Jane Goodall, refuted the idea that human tool use set us apart from our closest relatives. Perhaps the entire enterprise of looking for traits that distinguish us from other apes is misguided and the differences are more quantitative than qualitative?

Mind the gap

Last month I enjoyed the pleasure of discussing this topic with UQ’s Professor Thomas Suddendorf at the Sydney Writers Festival. Suddendorf was at the festival to talk about his book The Gap: The science of what separates us from other animals (Basic Books) recently published to enthusiastic reviews.

The Gap tackles the difficult question of what separates humans from other animals, but part of its genius is the way it begins by putting humans into a biological context. Only by viewing humans as organisms can we begin to test the idea that humans differ from other organisms, and what those differences might be.

Professor Thomas Suddendorf talking at TEDxUQ about the evolution of human minds and some of the science he writes about in The Gap

A psychologist, Suddendorf works with both human children and other primates to understand mental evolution and the development of those mental capacities in childhood. The Gap considers in detail the mental traits most likely to have effected the ecological success of humans relative to our great ape relatives. Where orangutans, gorillas and chimpanzees languish in ever-shrinking patches of rainforest, he points out, humans now make up more than seven times the biomass of all other wild mammals combined. Something sets us apart, ecologically at least, from our closest relatives.

After reviewing the current scientific evidence of human and ape capacities in the areas of language, mental time travel (the capacity to imagine the past and the future), theory of mind, intelligence, culture and morality, Suddendorf arrives at the conclusion that across these domains, two major features set humans apart:

Our open-ended ability to imagine and reflect on different situations, and our deep-seated drive to link our scenario-building minds together.

That’s as good an answer to the questions about human uniqueness as I have ever encountered. What is more, the answer, and Suddendorf’s fascinating path to that answer has made the very question of human uniqueness interesting again.


Couldn’t resist this 1988 Pixies performance of ‘Where is My Mind?’ Science has unequivocally answered the ‘Where’ question as well as resolving many of the evolved differences between our human minds and those of our surviving relatives.

The Conversation

Rob Brooks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

This article was originally published on The Conversation.
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