Do Hormones Really Influence What Women Find Attractive?

Recent replication studies torpedo earlier research on hormones and mate choice.

Posted Jun 05, 2018

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It’s no secret that psychology is in the midst of a replication crisis. Research findings previously thought to be solid and reliable have proven anything but, as teams of independent researchers have tried — and failed — to reproduce the results of dozens of experiments.

Why might this be? Well, scientists are under pressure to publish their research in prestigious academic journals. The editors of these journals often favor exciting and groundbreaking new findings, rather than the dull but necessary work of verifying the results of past endeavors.

I too might be guilty of focusing too much on the most eye-catching results: the results I think you will want to read about, but which may or may not be supported by later research. So today we’ll look at a few recent replication studies that have called into question some of the effects that I’ve written about before.

We’ll look specifically at research on how hormones influence women’s mate preferences and mate choice, partly because I personally find research in this area to be interesting, and partly because many of the results of these studies have been hyped in the media (and on this blog).

So, is women’s mating psychology affected by their menstrual cycle or their hormonal contraceptives? Let’s find out.

Hormonal contraceptives and relationship quality

Hormonal contraceptives, such as the pill or patch, are designed to reduce the likelihood that a woman will conceive a child after having sex with a man. But hormones have psychological as well as physiological effects, and so it’s reasonable to hypothesize that popping a daily pill chock-full of estrogen and progesterone — hormones that govern processes related to reproduction— might influence the way a woman feels about relationships and sex.

One idea that has received some support is the “congruency hypothesis”. The hypothesis goes like this: women enter into relationships while using or not using the pill; afterwards, some of the women who were using the pill stop using it, while some who weren’t using the pill start; if the pill affects sexual psychology, changes in pill use may cause a woman to be less attracted to her partner; conversely, women who haven’t started or stopped taking the pill since their relationship began should find their partner’s allure undiminished.

A woman who starts or stops taking the pill after her relationship begins is classed as “incongruent”, while a woman who sticks with the same regime (taking the pill or not taking the pill) is described as “congruent”.

A team of researchers led by Patrick Jern of Åbo Akademi University in Turku, Finland, recruited almost 1000 women who were in a relationship with a man. The women answered questions about the quality of their relationship and their sexual satisfaction with their partner, their jealousy, and their partner’s physical attractiveness.

Jern found that women who had used the pill when they met their partner, and women who were currently using the pill, tended to report higher sexual satisfaction. Current pill users were also more jealous. However, the key findings relating to the congruency hypothesis were not supported: women were no more or less satisfied with their relationship or attracted to their partner if their pill regime had changed or remained the same.

Jern, recognizing that there are different ways to be congruent or incongruent (women could start or stop taking the pill, or remain on or off the pill), tested for differences between these four groups of women. Consistent pill users tended to be higher than consistent non-users in sexual satisfaction and jealousy.

Jern and his team speculate that one of the reasons why previous researchers have found support for the congruency hypothesis is that the numbers of women in the different groups tend to be unequal. More women stop using the pill after their relationship begins than start using the pill, meaning that non-users are often over-represented in the incongruent group.

Hormones and macho men

Hormonal contraceptives are also thought to influence the type of man a woman finds most attractive.

In the interests of full disclosure, I should point out that a few years ago I co-authored a research paper showing that the pill might affect women’s preference for male masculinity. My colleagues and I found that women who used the pill when they started their current relationship tended to be paired with a man whose face was more feminine (a Ryan Gosling type), while women who hadn’t used the pill were partnered with men who were facially more masculine (think Dwayne “The Rock” Johnson).

Other psychologists have found that using the pill reduces women’s attraction to male facial masculinity, which may help to explain our results.

Recently, however, Ula Marcinkowska of Jagiellonian University in Kraków, Poland, repeated that research and (spoiler alert) blew it out of the water.

She had over 6000 heterosexual women report their pill use. The women then saw pairs of faces that had been manipulated using computer graphics software to appear more masculine or more feminine, and indicated which faces they found most attractive (click here for an interactive demo).

The experiment showed that women were no more or less likely to prefer masculine male faces if they were pill users than non-users (although, oddly, pill-using women did prefer feminine female faces to a greater degree than non-users).

It’s possible that women who use the pill end up in relationships with masculine men despite not finding them more physically attractive. Perhaps masculine-faced men have some other attractive trait that non-pill users find alluring, or are better able to compete with one another for access to non-pill using women. Marcinkowska’s findings don’t mean my own research will end up in the trashcan (phew!), but they do incentivize further work on the question of hormones and masculinity preference.

The menstrual cycle and mate preferences

Talking of which, you may have heard about the much publicized effects of the menstrual cycle on women’s preferences for various male traits, including masculinity. These findings emerged in the mid 1990s, and were explained using the “dual mating strategy hypothesis”, which suggests that women vary in their attraction to so-called “cads” and “dads”.

“Cads” are sexy bad boys who tend to appear sexy and masculine, but are less committed and generous. Based on the now increasingly shaky assumption that masculinity is related to heritable healthiness, a masculine man might make a good genetic fathers, but his personality might make him a poor bet for a long-term partner. “Dads”, on the other hand, make up for what they lack in sex appeal by committing to their relationships, and generally being friendly and nice. Seeing as women only have a good shot at conceiving with a “cad” when they are most fertile, a heightened preference for masculinity around ovulation might be useful. A preference for femininity at other times might lead women to benefit from relationships with a “dad” type.

A flurry of studies in the early 2000s provided evidence for the link between cycle phase and a preference for masculinity, showing that women do indeed find macho men more appealing at the most fertile time of the month. But more recent studies (and a series of technical research papers suggesting that the methods of earlier experiments were not sufficiently rigorous) have thrown these exciting discoveries into doubt.

Ben Jones of Glasgow University in Scotland recently led a team of researchers in an ambitious long-term study of the face preferences of over 500 women. These women reported to Jones’ lab every week for several months. On each occasion they provided saliva samples, and these were tested for hormones (the menstrual cycle is associated with relatively predictable changes in estrogen, progesterone, and luteinizing hormone).

The women also completed masculinity preference tasks that were similar to those used by Marcinkowska. The women judged which face — the masculine or feminine — was most attractive for a long-term and a short-term relationship, because past research has indicated that the cycle effect is strongest when women judge men for flings.

Analyses revealed that women generally preferred masculine to feminine faces, an effect that was stronger for judgments for short-term relationships. However, the fabled cycle effect failed to emerge. Women are no more likely to prefer masculine faced men when they are most fertile than at other times of the month.

Another recent study, headed by Julia Jünger of the University of Göttingen in Germany, investigated the effects of the ovulatory cycle on women’s preferences for masculinity in men’s bodies. This means it’s time for another disclaimer: I was a co-author on the original paper showing that women prefer buff men when they’re ovulating. In that study we recruited women over the internet and, based on their self-reported cycle phase, we estimated whether they were likely to be at peak fertility at the time they rated the images. Jünger’s method was substantially more robust: she tracked the same women over two cycles and, like Jones, collected saliva for hormone testing.

The results of this newer study show that, when fertile, women rate male bodies as more attractive. But the change in attractiveness is general across all male body types: both feminine and masculine male bodies are more attractive to a woman in the fertile phase of her cycle.

And (because she clearly likes keeping busy) Jünger has also conducted a study of cycle effects on women’s preferences for masculine male voices. Several research teams have shown that, when most fertile, women prefer a man with a deeper voice. However, some of those teams estimated women’s cycle phase based on when her most recent period began, rather than by checking her hormone levels.

Just as facial photographs can be made to appear more masculine or feminine, recordings of voices can also be manipulated to sound deeper or higher. Jünger also had her volunteers rate the attractiveness of recordings of men that had been shifted up or down, as well as recordings of men whose voices naturally varied in pitch (this more naturalistic experiment can demonstrate whether an effect is likely to persist in real-world situations).

At this stage it should come as no surprise to you that Jünger found no effect of the cycle on women’s preference for men’s vocal masculinity. However, deeper voices were rated as more attractive than higher voices, and women generally rated men’s voices as more attractive when they were in their fertile phase.

In another paper that was published just as I was putting the finishing touches to this blog, Ula Marcinkowska (busy busy busy) confirmed once more that masculinity preferences do not vary with cycling hormones. However, she did find that a woman’s average level of hormones across the cycle were important: higher average levels of progesterone were associated with a stronger preference for masculine men, but only among partnered women — for single women, the pattern was reversed.

The results of both of Jünger’s studies suggest that there is likely something happening over the menstrual cycle — women are perhaps more sexually motivated when fertile — but interest in masculinity appears to be unchanged. Marcinkowska’s study suggests that hormones are related to masculinity preferences, but not in a cyclical fashion, and that it’s important to account for other variables, such as relationship status.

Either way, the evidence for the dual mating strategy hypothesis is considerably weaker than it once was.

One step back, two steps forward

You might now be wondering whether you should take every psychology article with a pinch of salt. How can we trust the results of any study?

Science works by a process of incremental advances. Psychologists who develop novel hypotheses are often at a disadvantage: as they stride out into the unknown, they might be unaware of the tools and methods that are necessary for robustly testing their theories. Only later, with the benefit of hindsight, can other researchers see where improvements can be made.

Also, all psychologists have to decide how best to invest their time, effort, and funding. When an idea is new and has little or no data to support it, it can be difficult to justify investing heavily in it. Afterwards, when an idea has the weight of evidence behind it, psychologists may find it easier to argue for re-testing the hypothesis with a bigger sample of volunteers, more expensive methods (such as hormonal tests), and for establishing international collaborations to recruit culturally diverse volunteers.

There will always be findings that, after the initial exciting phase of the investigation is through, prove difficult to replicate. This is why we should never take the results of one study as definitive and unshakable evidence of some underlying truth, and why all of us — professional psychologists and interested laypersons alike — should be supportive of the efforts of those who are willing to look beyond the headlines.

References

Jern, P., Kärnä, A., Hujanen, J., Erlin, T., Gunst, A., Rautaheimo, H., . . . Zietsch, B. P. (in press). A high-powered replication study finds no effect of starting or stopping hormonal contraceptive use on relationship quality. Evolution and Human Behavior. doi:10.1016/j.evolhumbehav.2018.02.008

Jones, B. C., Hahn, A. C., Fisher, A. D., Wang, H., Kandrik, M., Han, C., . . . DeBruine, L. M. (2017). No compelling evidence that preferences for facial masculinity track changes in women’s hormonal status. bioRxiv. Retrieved from https://www.biorxiv.org/content/early/2017/12/29/136549

Jünger, J., Kordsmeyer, T. L., Gerlach, T. M., & Penke, L. (2018). Fertile women evaluate male bodies as more attractive, regardless of masculinity. PsyArXiv. Retrieved from https://psyarxiv.com/nyba6/

Jünger, J., Motta-Mena, N. V., Cárdenas, R. A., Bailey, D. H., Rosenfeld, K., Schild, C., . . . Puts, D. (2018). Do women’s preferences for masculine voices shift across the ovulatory cycle? PsyArXiv. Retrieved from https://psyarxiv.com/k9y7s

Marcinkowska, U., Hahn, A. C., Little, A. C., DeBruine, L. M., & Jones, B. C. (2018). No evidence that women using oral contraceptives have weaker preferences for masculine characteristics in men’s faces. Retrieved from https://osf.io/2n74d/

Marcinkowska, U., Kaminski, G., Little, A. C., & Jasienska, G. (2018). Average ovarian hormone levels, rather than daily values and their fluctuations, are related to facial preferences among women. Hormones and Behavior, 102, 114–119. doi:10.1016/j.yhbeh.2018.05.013

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