Women are usually fertile in the days around ovulation. Do you behave differently in this phase than usual? Recent studies contradict the popular theory that mid-cycle women prefer a different type of man, reports psychologist Lars Penke of the University of Göttingen. But he and his team were able to observe cyclical changes in the female psyche.
“Spektrum.de”: Professor Penke, could you briefly explain what happens in a woman’s body during a menstrual cycle?
Lars Penke: The woman’s menstrual cycle is controlled by sex hormones. The body releases the hormones in a specific sequence over a period of about 28 days. This hormonal cycle ensures that an egg cell matures and women are fertile for a short time. If the egg cell is not fertilized, it is broken down again with the uterine lining and menstrual bleeding occurs.
Why are psychologists interested in this?
We explore how experience and behavior change over the menstrual cycle. The messenger substances that control the cycle reach all parts of the body via the blood, including the brain. They bind to receptors there and thus influence our experience and behavior. Above all, the level of estradiol and progesterone, an estrogen and a progestin, fluctuates. These are sex hormones that are found in significantly higher doses in women than in men. The special thing about this research is that with the hormones we have a physiological substrate that triggers the psychological effects and that we can measure.
How do you do that? How do you determine what cycle phase women are in?
The most direct way is to measure hormones in the blood. However, this is quite time-consuming, partly because the free, bioactive parts of the hormones first have to be separated from the protein-bound parts in the laboratory. We therefore work a lot with saliva samples. The values that are obtained there are delayed by a quarter of an hour, but for most studies this makes no difference. Of course, you can also ask the women to monitor their cycle themselves, as long as they don’t take hormones and have a regular cycle. The standard cycle is 28 days and usually varies between 24 and 32 days, although there are larger outliers. Ovulation is calculated backwards based on the following menstruation because the phase after ovulation is more constant than the phase before: if the cycle fluctuates, it is more likely in the period between menstruation and ovulation. Nevertheless, this method is comparatively imprecise. The gold standard would be to measure the luteinizing hormone, which triggers ovulation, in the morning urine. It rises rapidly about a day before and falls just as quickly afterwards.
Is it also possible to observe ovulation directly?
This would be possible using ultrasound, but it is too complex and invasive for our research. Some women even notice ovulation themselves. This is because the ova are the largest cells in the body, so the cellular processes may be noticeable.
Is it possible to see from the outside of a woman whether she is currently fertile?
In many species, the females are only intermittently fertile and sexually active, so they make that clear. For example, in our closest relatives, the chimpanzee and bonobo, there are clearly visible changes such as rectal swelling at this stage. An entire branch of research has therefore searched for such cues in humans – in vain. It has long been thought that ovulation in women is hidden so that men cannot know exactly which offspring are their own. Our babies need care for a very long time, and fatherly support helps with that. But if men knew exactly when a woman is fertile, it would be easier to keep looking for a fertile woman. If they don’t know this, it is wiser tactically for passing on one’s genes to focus on one female and her offspring.
And there is actually no recognizable indication?
There may be minimal effects in terms of facial skin redness, but so subtle that they are not visible to the human eye. Everything was examined: the appearance, the smell, the pitch of the voice, the behavior. For example, do mid-cycle women tend to wear red clothes? There were initial indications, but the findings were not confirmed. Much has been reviewed in the past seven years. The menstrual cycle does something to women psychologically, but it’s not what it’s supposed to be.
Perhaps the most discussed question was whether mate choice preferences are changing: do women around ovulation find a more masculine type of man more attractive? There were studies on this in well-known journals such as »Nature«. Images of men were computer altered so that the facial features or body type were more or less masculine, and the female subjects were asked to indicate which image they liked better. In a similar way, one also searched for preferences for deep voices or dominant behavior. There was a meta-analysis on this in 2014; it confirmed the idea of a woman’s »dual sexuality«.
What do you mean with that?
According to this theory, women’s sexuality is more reproductive on the fertile days, and women tend to prefer men with the “best genes.” The rest of the time, sexuality is increasingly geared towards the social function, i.e. towards the bond in the couple relationship. So a woman with a caring partner would find masculine men more attractive around ovulation. And men should be able to recognize these phases and then make a special effort. Various working groups, including ours, have tested these assumptions with extensive studies over the past few years. Almost nothing could be confirmed. The idea of dual sexuality has been refuted, the burden of proof is overwhelming.
But you also found cyclical changes?
Yes. The most robust effect relates to sexual interest: women are more interested in sex around ovulation. But her taste in men remains the same. In a study, we tested whether their preferences change over the course of the cycle. The result was: Close to ovulation, women find all male bodies a little more attractive. So it’s about sexual interest in general, called “libido” or “sexual drive” after Freud.
How about women’s bodies?
In general, straight women can also find women attractive; they are not as fixated on the opposite sex as straight men are. However, the effect described, the increasing attraction in the middle of the cycle, only applies to male bodies. Unfortunately, there is almost no psychological menstrual cycle research for homosexual women. On the one hand, because the theories are about evolutionary advantage, on the other hand, because it is difficult to recruit larger homosexual samples, especially for the rather laborious cycle studies.
What happens when women take the pill?
The changes in the middle of the cycle are not found in them. Roughly speaking, hormonal contraceptives prevent ovulation by keeping the hormones more constant; so the psychological changes do not occur. However, there are effects that have to do with the physical discomfort during menstruation: In this phase, sexual interest tends to decrease, even in women who take the pill. Psychological effects such as premenstrual syndrome can of course also be found in them.
Back to the women who do not use hormonal contraception. Do the fertile days show up in any other way than increasing sexual interest?
In any case, the biggest effect is that they become more interested in sex around ovulation, with their own partner as well as potentially with other men. In addition, women also find themselves more attractive around ovulation. According to new findings, this is also reflected in self-confidence, so that women can become more dominant and researcher. And another effect is quite robust: In the second half of the cycle, between ovulation and menstruation, women report that they eat more. There is even evidence that the weight varies around 200, 300 grams. This could also be due to increased water retention. But increased appetite is also found in other species, such as rhesus monkeys. If you offer them cookies, they will eat more in the second half of their cycle.
Are the psychological changes expressed in social behavior, for example with a greater desire to party?
Yes, but much weaker than the increase in sexual interest. And that doesn’t go down to the level of clothing. Whether looking at photos or having women draw what outfit they would like to wear if they went out today, we found no differences between cycle stages.
Is there no truth to the myth that waitresses get more tips around ovulation?
I’ve read about it in the press, but as far as I know there hasn’t been a scientific study on it. However, there was a similar study by Geoffrey Miller in New Mexico involving lap dancers, women who make money dancing in front of single men in light clothing. In an online diary, they noted how much tip they had earned in one shift and when their last menstrual period was. Women who did not use hormonal contraception received significantly more tips around ovulation. The sample wasn’t large, but the study attracted a lot of attention. To my knowledge, however, the result has not yet been replicated.
All of these findings relate to women who are able to have children. What happens after that?
The findings described are limited to the reproductive lifespan up to menopause, i.e. the last menstrual period. Then the hormone cycle stops and with it the psychological effects. Incidentally, there are few other species that have an ovulation cycle and menopause like us, belugas and narwhals for example. Evolution has established that women cannot have children until old age. On the one hand, there is an increased risk that they will no longer be able to raise their children; on the other hand, it helps the grandchildren if they are available as grandmothers. The effects triggered by hormones are also expensive, only a healthy body can afford it. This is why sick and malnourished women release fewer hormones. But even regardless of age and fitness, there are big differences between women. Some experience very clear psychological effects around ovulation, others none at all.
According to traditional ideas, the cycle is more a woman’s affair. Does it happen that other people find it strange that you, as a man, are so concerned with it?
No, the subject interests many, and it is seen as emancipated that I, as a man, am familiar with it. But I don’t just deal with the menstrual cycle, but with hormones and their effects in general, such as testosterone in men.
What fascinates you so much about hormones?
They have a very broad effect on the body and psyche. They put us in a kind of different mode, just like emotions. For example, when we’re feeling fear, everything else becomes unimportant – even physiology works differently. It’s similar with hormones: When men have high testosterone levels, they tend to be more dominant, competitive, less nurturing. What interests me most is what it’s actually good for. We have been optimized by evolution. It is no coincidence that our bodies are the way they are.
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The original of this article “Myth refuted: “Cycle does something to women, but not as expected”” comes from Spektrum.de.