#1284 Lars Penke: Do Women's Mate Preferences Change During Ovulation?

00:00 Ricardo Lopes: Hello everyone. Welcome to a new episode of the Dissenter. I'm your host, as always, Ricardo Lobs, and today I'm joined by a returned guest, Doctor Lars Penke. He's full professor of biological personality Psychology at the University of Gottingen, and today we're going to explore the evolutory shift hypothesis, what it is and Uh, studies that Dr. Pene and his collaborators have been doing over the past few years to test this hypothesis and the several different predictions that come out of it. So, Doctor Pena, welcome back to the show. It's great to see you again.

00:37 Lars Penke: It's a pleasure to be here again.

00:40 Ricardo Lopes: So let's start. I mean, I think that we've touched at least briefly on these hypotheses in our first conversation, but I mean just for people who might not be familiar with it and perhaps to update. Some of what's been going on surrounding these hypothesis in recent years. What is it really about and what are the main predictions that people have been putting forth that supposedly derived from it?

01:14 Lars Penke: Yeah, so the ovulatory cycle shift hypothesis uh concerns the female ovulatory cycle. So women emit steroid hormones cyclically across their monthly ovulatory cycle, and that is primarily related to reproductive functioning. So it's related to Uh, the ripening and the release of the ovum of the eel and, uh, its implementation, so it's preparing for conception and pregnancy, and hormones are extremely interesting molecules because they usually don't only have a local effect but have effects all over the body and that includes our brain and our psychology. And therefore, there is a huge field of behavioral endocrinology that is concerned with how hormones affect behavior and that intersects very much with evolutionary psychology because always when something is related to reproduction, then it is close to biological functions related to evolution. The ovulatory cycle shift hypothesis in particular is concerned with how female psychology changes across the ovulatory cycle. And um it's a plausible idea that it does, and there have been over the years, many ideas what exactly shifts. So in the very early days, there were ideas, for example, that uh how women categorize people into male and female and how much attention they pay to whether somebody is male or female shifts across the ovulatory cycle. There have been studies about uh spatial perception across the ovulatory cycle and so on. But The version of the ovulatory shift hypothesis that steered so much debate over the last 10 years or 15 years almost. Um, IS a version that assumes that female mating behavior changes in a way that we could almost say there are two kinds of female sexuality, one related to ovulation and one related to sexual activity outside of the ovulatory window, and that has been called the dual sexuality hypothesis. And The original propositions that have been put forward in that regard is that women only can get pregnant during ovulation, whereas in our species, women are sexually active. All around the ovulatory cycle and also even when they are not ovulating, uh, and so that there's a sexuality that is related to adaptive problems of conception and whom they become pregnant from, and there is a psychology related to sexual activity when uh pregnancy risk is very low. So what has been put forward in this regard is that female mate choice has two goals, two components. One is regarding direct benefits of mate choice, and that is everything that directly helps the woman getting pregnant and uh. Yeah, raising children, so there are male preferences for things like male resources, male support, male protection, also simply male fertility. And on the other hand, there might be made preferences for indirect benefits that include everything that the sire passes on to the offspring and therefore benefits the offspring and not directly the mother with her pregnancy. And these indirect benefits would be anything that genetically is transmitted from the father to the offspring. Now, the idea here is that some Potential sires, some potential partners might have genetic qualities that they can pass on to offsprings that are only relevant during sexual activity when conception is likely, and these have been termed good genes in the literature, although in genetics, people cringe a little bit when you call it good genes because there is no intrinsic good or bad value to genes. But you could translate it to something like new, uh, like low mutational load, so few rare events in the genome that disrupt anything in the genome, you could translate it to, uh, genetic endowments that fit very well the environment or that are very compatible with the mother and all of that together, we could call good genes. And This idea which we often call the good genes ovulatory cycle shift hypothesis in the literature is concerned with whether women prefer different partners, different partner qualities for sexual partners when conception is likely. Now, the interesting bit of this hypothesis is that we are a long-term binding species, so we tend to have long-term relationships, not only meeting up for sexual activity as some other species do, but forming long-term bonds. And if you form a long-term bond, you have a trade-off between these different kinds of qualities potentially. You might be lucky and find somebody who Uh, entails all these qualities, but you might face trade-offs, and in this case, it might be that female preferences for partners shift over her cycle and that she would prefer a different partner when she's ovulating and when she's in different phases of the menstrual cycle or when she's pregnant or lactating or whatever, so non-ovulating. And so a consequence of this idea of the good genes ovulatory cycle shift hypothesis is that within one long-term relationship, a woman might prefer different partners, different uh um uh qualities, different traits of sexual partners when she's ovulating. Than when she's not, and if she is so unlucky and doesn't find a perfect partner that entails everything, she might even be motivated to um be sexually unfaithful during ovulation and because of this very provocative uh. Yeah, consequence of this hypothesis, uh, there's been a lot of debate about around it.

08:17 Ricardo Lopes: So, uh, uh, that's the hypothesis and the several different predictions that stem from it. But how have you been, uh, you and your collaborators have been evaluated, uh, have been evaluating it in your recent studies, and, uh, I mean, what would you say are perhaps the best study designs to properly test the predictions that stem from the ovulatory shift hypothesis?

08:46 Lars Penke: Yeah, it is a very complex hypothesis and that's why study designs are quite important. And there have been a huge amount of studies, dozens of studies already around 2010, up to 2010, so this hypothesis came up in the late 19990s. And then it has been studied very intensely, and there have been a whole array of studies that try to test it, usually with asking women in which phase of the menstrual cycle they are and then presenting them different kinds of stimuli, faces, voices, videos with behaviors, with dense behavior with competitive behavior, or, or simply uh vignettes with descriptions of partners and so on. Um, AND there have been studies that looked at sexual interest that women have for their partner versus potential partners outside of their relationships, which are then based on self-reports basically. There were so many studies on that, that there have been not one but even two meta-analysis, both published in 2014, which came to astonishingly quite different conclusions with regard to if these ovulatory cycle shifts existed and that was around the time when there was a lot of debate in science in general and especially in psychology about the replicability of findings. So this. Debates really started with uh exactly the same point as the replication crisis in psychology, so. Our lab was one of several who said we need the sizes of studies there and I actually, full disclosure was a huge proponent of this whole ideas of uh cues to uh genetic quality of uh ovulatory cycle shifts. I was actually. Thinking or or or aiming for confirmatory studies because I was theoretically completely convinced by this hypothesis. So what, what we originally did, we started off with a large online diary study where we recruited both women with natural cycles, ovulating women. And women uh on hormonal contraception, which could be used as a quasi-control group because hormonal contraception basically, um, Yeah, takes ovulation away and, and evens out the hormone profile across the cycle. And we asked these women more or less on a daily basis, several things, but we Primarily asked them about their sexual interest in a potential partner, in uh, if they had a partner in their partner, uh also in uh other men, and we asked a lot of detailed questions that we're getting at these predictions of the um good genes ovulatory cycle shift hypothesis. And by far and large, we didn't find much in that study with regard to the specific predictions. We did find a lot with regard to shifts in general sexual interest and everything that could be related to that, so that women felt more attractive themselves when they were ovulating, that they had more sexual interest, that they had more masturbation interests, that they had. Uh, MORE interest in being social and interacting with men and so on that they perceived more flirting attempts and so on. So there was a lot going on which is in line with the greater, uh, yeah, presence of a, of a sexual mindset, so to speak, but the specific predictions by the good genes ovulatory cycle shift hypothesis, um. Were not very well confirmed and then we went on to do other studies that included multiple testings of women in the lab that included detailed hormonal measurements based on saliva hormones and on urine tests. And we presented them with all kinds of stimuli for which it has been proposed that these preference shifts should happen. These included. 3D scans, rotating 3D scans of male bodies, which could entail information about masculinity and all kinds of other traits that have been proposed to be related to male-made quality, uh, and also to genetic quality. We, uh, used voice samples that, uh, should. Include information about how deep the voice is, so about the fundamental frequency of the voice, which has been very much discussed as an indicator of uh male quality and especially also genetic quality, and we also used videotapes, for example, um, of uh male courtship behavior, flirting behavior. And We had rather strong designs both in terms of sample sizes, in terms of direct hormone measurements of longitudinal assessments as opposed to cross-sectional assessments of uh female fertility, but also in terms of statistical. Analysis and also in terms of how carefully we tested our analysis against potential uh um yeah, decisions that could be debated, so different forms of determining uh ovulation status, different forms of uh analyzing the hormones, different uh forms of uh control variables, and so on. And by far and large, we didn't find much there as well, so it didn't seem to be the case that preferences for voices, bodies, behaviors, and so on. Shifted very much. Other labs at that time uh studied other traits, for example, faces and all the detail, and there wasn't much evidence there either. The only thing we found in some studies, it's not a huge effect, but it is a fact that uh occurred in some of these analysis is that women preferred all kinds of men more when. Ovulating when around the ovulatory point in their cycle, indicating that the general preference for men, these were all heterosexual women by the way, but the general preference for men was higher, but the rank order of men was completely conserved, so that means even the least attractive. Men as rated by these women were still rated a little bit more attractive when they were ovulating, so no preference shifts but a general attraction effect.

16:07 Ricardo Lopes: Oh, OK, so, uh, but, but if there's really this, um, shift in terms of their, uh, sexual, in terms of their sexuality in the sense that, as you said, they are more interested in just all kinds of men, men in general, when, when they're going through ovulation, uh, what would be, or, or would there be an evolutionary rationale for that in any way, um. I mean, and, and does it link, uh because we tend to think from, at least from an evolutionary perspective, uh, as women, women, because, I mean, they have to bear the costs of uh pregnancy and usually. Also, the costs of child rearing and all of that, and I mean they can only get pregnant once at a time. I mean we tend to think of women as being choosier than men. I mean, does that relate In any way to this shift in terms of their sexuality at all and and would it in any way invalidate that idea that women are really pickier than men or not or am I or am I just perhaps mixing things here that shouldn't be mixed.

17:38 Lars Penke: I, I think these are two different aspects. So there's a lot of studies on human-made choice that show that women generally are pickier, but not necessarily, it doesn't necessarily entail that anything about that changes across the menstrual cycle. The phenomenon that is behind all of this in a way is the idea of estrus. Estras is the term that is used in the animal literature, usually in the non-human, uh, animal literature. Describing that in many species, the period around ovulation is accompanied by clear behavioral changes. I mean, the ovulatory cycle is a very evolutionary old phenomenon. It is certainly changed uh uh shared by all mammalian species, and in many species you see that. Receptiveness, so the acceptance of copulation attempts by females is limited to the time of ovulation. In some species it's even more pronounced in the sense that females actively. Uh, ACTIVELY, uh, Uh, approach copulation attempts or advertise themselves, for example, in, in rats and mice, there's this, uh, phenomenon of low doses that they present their back basically, um, because they are willing to copulate, um, uh, under these circumstances. In some species, it's even called heat because it's such an obvious phenomenon. And in some species you even have changes in female attractiveness with ovulation, even in our closer relatives in the primates in some. You have, uh, sexual swellings even in our closest, uh, relatives like uh chimpanzees and bonobos. In other species like some, uh, baboon species, you have, uh, vocal callings, uh, when female, uh, are ovulating and some marmosets, you have clear chemical cues that they smell differently to the males and all these phenomena together are usually called estrus and the Idea that was also discussed around the ovulatory cycle shift a lot is, is there something resembling an asterisk in human females as well, so could it be that. Well, it's, it's certainly not as obvious as, for example, in chimpanzees or bonobos where behavior changes dramatically and also visible changes are dramatically there that even humans can easily see them. But could it be that some aspects of Eros are also there and our species are probably evolutionarily conserved and Our findings and also the findings of others including some of these large scale replication attempts around this literature clearly indicate that that is the case. Female sexual interest seems to be the one robust thing that changes with ovulation and that is highest during ovulation. So, um, that makes a lot of evolut uh uh evolutionary sense because. If evolution in the end in sexual species is about reproduction, then when conception is likely, sexual interest should be highest and sexual opportunities uh should be seized that way. That makes a lot of sense. The question is, is it related to mate choice, and that is what you were alluding to. On the other hand, that, yeah, I mean the old mantra in evolutionary sciences is, um, males compete, females choose, of course, there are many exceptions to that rule, but female pickiness, female choosiness is a widespread phenomenon. But humans are a species that. Usually Uh, reproduces in pair bonds. So pair bonding is a widespread human phenomenon as far as we know it exists in all human societies and it's probably the ancestral state as well. We don't need necessarily to talk about lifelong monogamy. That is, of course, a modern cultural invention that might. Have, uh, a long religious history and cultural history, but that humans form longer term bonds, especially around rep reproduction is a widespread phenomenon. And the key moment when mate choice is important is the long-term partner choice. Now the ovulatory cycle shift hypothesis, the good genes ovulatory cycle shift hypo hypothesis, moved that away from that a little bit and said, yeah, well, there might be long-term partner choice, but, Genetic sire choice whom to copulate with when conception is most likely might be different from that, and that is at the core of this dual sexuality hypothesis. And that is the part that has been put very much in question by the recent literature, so, uh, of course, women are choosy when it comes. Uh, WITH regard to long-term sexual partners, it's probably also are choosy when it comes to, uh, short term mates with whom they might have affairs or one night stands, but that doesn't need to be tied to the ovulatory cycle or at least that, that is a specific hypothesis that can be tested and that has happened in the last. 10 years.

23:34 Ricardo Lopes: OK, great. It's very important to clarify that point. So, and how about preferences for men's behaviors, like, for example, competitive or courtship behaviors, because I imagine that that would be an issue that is separate from just their. Uh, REFERENCE, their made preferences in terms of, uh, uh, having good genes or not, not, not so good genes or other physical traits. So are there, is there any shift in terms of, uh, preference for these kinds of behaviors during ovulation?

24:17 Lars Penke: Well, the question is, what do these behaviors transmit in terms of information, so what information is there for the women to decode from these behaviors and. Many predictions have been floating around in the literature. The original good genes ovulatory cycle shift hypothesis has discussed all kinds of male behaviors as indicators of genetic quality as well that included some ideas about uh male dense behavior indicating uh a well-built and even symmetrical body and so on, so that a well put together body. Is able to show better dance moves, that was an idea that was around there, but most of them really related to masculine behavior that is probably related to testosterone and that elicits uh intra-sexual competition or male male competition, so confident uh appearance, um. Yeah, uh, daring behavior, risky behavior, or maybe even, um, uh, um, direct approach behavior and so on. And that is all related to the same predictions, um, that, that, or, or to the same ideas that are also behind, uh, other, uh, made preference shifts that have been predicted in the literature, namely that individuals with male individuals with higher testosterone. Are preferred during ovulation because it ties back in one way or another to genetic quality, so either, High testosterone is directly linked to higher genetic quality and that has often been linked to it via the immunocompetence handicap hypothesis that testosterone lowers uh immunocompetence and that therefore only genetically fit individuals could allow that, that hypothesis has all kinds of problems and has been. Uh, EVEN on a theoretical ground when challenged a lot. And the other idea is that only men with high genetic quality are in such a position that they have competitive advantages that they can allow themselves to show daring behavior, competitive behavior. I don't know, even aggressive behavior or, or, um. Even in the presence of other men. It all boils down basically back to this idea is testosterone related to genetic quality and are testosterone linked traits, be it facial or bodily masculinity, deep voices, or some parts of behavior, are these indicators of genetic quality, because otherwise I mean women might just like confident men because. They get things done. They are good providers of resources. They might prefer stronger or high status men because they are better at providing protection and so on. So there are a lot of testosterone linked traits that would entail direct benefits that are not necessarily tied to conception risk to the ovulatory phase of the cycle. These kinds of Traits of qualities women should prefer. Uh, AT any time, but not only at specific parts of the cycle, but only if you link these behaviors in one way or the other back to genetic quality, the ovulatory cycle shift hypothesis even makes theoretical sense. And this whole link between testosterone and genetic quality is sounded pretty convincing around the 2000s, but uh it's probably not the strongest candidate anymore. So if we would really be serious about the good genes ovulatory cycle shift hypothesis, we should actually move towards traits where we now, after 20 years, 25 years of genomic research since the human genome was decoded, where we now know that these are traits that are tightly linked to. Genetic quality as it has been defined in the evolutionary literature, so for example, mutation load, and that would rather be traits like. Absence of psychopathologies, probably intelligence. Maybe some other aspects of physical appearance, but especially traits like intelligence or absence of psychop pathologies like schizophrenia, autism, uh, um, epilepsy or so on where the evidence is pretty strong that they are related to mutational events. These traits have rarely been studied with regard to links to cycle shifts, and if they have been studied, they usually didn't show much of an effect. So the absence, for example, of a cycle shift for preferences for intelligence is actually also something that doesn't sit very well with the good genes ovulatory shift hypothesis.

30:07 Ricardo Lopes: Right, so I would like to ask you now about some of the predictions that have been made when it comes to changes in women's behaviors during ovulation or even cues to fertility. So is there any evidence to support the idea of an increase in women's general attraction during evolution? I mean, I do. Or do they appear more attractive to men when they are ovulating or not?

30:43 Lars Penke: Yeah, yeah, that was another part of ovulatory shifts that has been discussed a lot. It's not necessarily tied to the good genes ovulatory shift hypothesis, but it is tied to this idea of an asterisk. So if we look at Female chimpanzees or female bonobos during ovulation, we see these rectal swellings that are extremely visible and so the most direct idea would be that hormones have a direct effect on the female body that translates to a higher attractiveness and it's certainly not as obvious as the. Primate shifts because women simply don't have these kinds of swellings and if anyone should be able to see these changes if they happen, then it is males of the same species, so us. But there has been this idea that, yeah, well, there might be leaky cues that are still there and showed a little bit or there might be vestigial cues that have been more relevant in the past and uh are still perceivable now and so things like changes in the female face have been studied, like coloration of the female face. Symmetry of the breasts, uh, changes in the voices, changes in the smell, changes in the gait or in the uh dancing behavior or, or movement behavior of women and so on. Again, there have been some studies early on that seem to show these effects, but they were still of the kind that usually didn't have the strongest designs and the stronger replications usually didn't find much. So for example, if we take changes in facial coloration, which would be a very obvious one because we know that hormones that change across the ovulatory cycle like estradiol have effects on the blood vessels and could actually change facial coloring, so for example, facial reddening. These changes are not immediately obvious. In some studies, when you directly put photos of women from different ovulatory faces next to each other, they found some effects and others didn't find any effects, and it doesn't seem to be obviously perceivable at all. There was one study that directly tested for the red coloration of the faces and found that there was a tiny effect. But that effect was so small that it was below the visible detection level of the human eye. And that basically disqualifies it as any kind of evolved signal or even as a perceivable leaky cue and that brings us to a very interesting point because sometimes these studies try to squeeze out statistical significance in one way or another, but for. Something to be evolutionarily relevant, it should have a sizable effect so that even in the long run across generations, it could make an evolutionary difference. And so what we need really is for these kinds of effects the smallest effect size of interest. There are now statistical tests. That you can test if an effect, even if you find it statistically significant, is big enough to make a difference, but for that you have to define, and that's something you can only do theoretically. You have to define how small an effect can be to still make a difference. But if something is not detectable by the human eye anymore, it will certainly fall below this threshold of the smallest effect size of interest and for red coloration in the face. That is certainly the case. Now, this whole literature also moved beyond that and thought, well, maybe, uh, may may maybe let me add in something that hasn't been studied a lot but that would make for a very interesting and, and plausible cue of ovulation is smell. So olfaction studies are rare in humans because they are complicated to do. And they are often not very promising because we are not a very olfactory-driven species, so compared to a lot of other species, including a lot of primates, we are way, way more dependent on our visual and auditory senses and not so much on our olfactory senses, on our sense of smell. But it would still be plausible that hormones change female scans over the cycle so that males would be able to perceive that. If that's relevant in everyday life situations, it's a different thing because we have high standards of body hygiene and uh we usually use perfumes and uh other bits, but it could still be that there are detectable changes there. Um, WHAT we did in the last few years is we did a big study on females across the ovulatory cycle, including longitudinal hormonal measurements and including samples of both their axillary and their vaginal smell. So we had women wear basically cotton pads under their arms and in their pubic region. Over a cycle and we collected them and gave them male participants to evaluate regarding the smell, regarding the intensity and the pleasantness of the smell, but also directly regarding the attractiveness of the smell and. By far and large we found nothing, so there were no changes in male ratings of these cotton pets, these smell samples, but we also did gas chromatography analysis of the chemical compositions of the smells to see if anything changes with regard to the chemicals in the smell across the cycle, because if there are some. LEFTOVER products from physiological processes that end up as detectable molecules in these samples, then they should be there on these cotton pads and they should be analyzable and even that didn't. YIELD any convincing results, so there isn't even a chemical change that could potentially be detected. So we can basically cross off chemical cues as something to change over the ovulatory cycle as well. Now if I might add to that bigger part of the literature in humans is do women present themselves differently because we are a species that. Does not evaluate others simply based on their physical or on the bodily uh um appearance, but that also looks at how we present ourselves in terms of clothing, in terms of grooming and all these kinds of aspects. And there have been studies in the literature that proposed that women dress differently, for example, uh, wear more revealing clothes, show more skin, wear more conventionally, uh, uh, attractive clothing, choose different colors for their clothing, or for example, for their makeup, and there was also this idea that similarly to the sexual swellings and other primate species. And pink should be the colors that we are evolutionarily adapted to, to react to in the sexual context. So people looked at red lips lipstick and uh red uh nail polishing or red or pink clothing and so on. There were some studies that found these effects and, and discussed them as pretty relevant, but then bigger replication studies came, including some of ours and we, we, we published a paper, Julia Stern and um Sabio Ostermann and I published a paper a few years ago where we replicated all kinds of ideas that have been proposed in that regard in the literature in 5 studies. And we basically found nothing at all. To the contrary, some of the effects were in the opposite direction that women apparently uh wore more sexy clothes, if you want to put it that way, when they're in the, when they were in the non-fertile phase of the cycle. So by far and large we again see a huge Null finding there and that at least puts a big question mark to uh a lot of ideas that have been proposed originally.

40:01 Ricardo Lopes: OK, so I, I mean, at this point in time, what can we say about the possibility of there being any cues to fertility in women during ovulation? I mean, are there any cues at all that have been supported by the scientific evidence?

40:23 Lars Penke: Well, if there are any cues at all, there are in the female behavior, and that is something that we found in our online diary studies that women have different behavioral tendencies when they are ovulating and that might be rather directly linked to that shift in sexual motivation. So the sexual desire effect is there, it is pretty robust. And we found that women It's another thing that we found very robustly across several samples is that women perceive themselves as more attractive. So women feel more attractive when ovulating. It's not a general self-esteem effect, it's not a general positive affectivity effect, so they are not simply more happy when ovulating, but they specifically feel more attractive when ovulating and. Our diary studies also point to the fact that they are behaving differently based on that. They are more social, they are more flirty and all uh um uh things like that. One big study that we did with my former PhD student, uh, Lara Schleiffenbaum was a couple diary study where we had 384 heterosexual romantic couples that were in steady romantic relationships. And we had both the men and the woman in that relationship answer a couple diary, and we asked them questions about themselves, but we also asked both of them questions about their partner, how they perceived the partner that day. We actually framed it a little bit as a couple quiz that on a daily basis, they should say how they feel and how the other partner feels, and we had all kinds of items. A lot of them were also regarding uh sexual interest. And in that study, again, we showed very clearly that women had higher sexual interest when in the ovulating phase of their cycle, there was even some tendencies that they initiated sexual contact more or try to initiate sexual contact more. But the funny thing was the male partners didn't seem to notice any of that. So when you look at how these men rated on the same day, how much sexual interest they perceived uh from their partner, these were usually even cohabiting couples, so they had plenty of time to see something, uh, what was going on in their partner. They didn't seem to pick up on anything there. And I mean the. Evolutionary psychological literature made more specific predictions with regard that men should pick up this heightened sexual interest in women and react to it not only by sexual interest but also by, for example, be potentially more jealous because if these women feel more attractive and behave more attractive and behave more flirty and more social and so on. And men really picked up on that, then they might get more jealous or they might be more interested in occupying the time of that woman, which is sometimes called mate retention or mate guarding behavior in the literature. And we asked for these kinds of behaviors as well, and there was no effect of the female cycle status on these kinds of behaviors as well. So it doesn't seem to be the case that men really perceive something there and. So yes, women feel differently, are differently motivated when ovulating, and might actually show related behaviors, but if they are not even translating to different behaviors in the male partners, then it's very unlikely that they. Change behaviors and, and other men that only briefly observe the women either.

44:23 Ricardo Lopes: Uh LET me just ask you, and this is more of a theoretical question, but uh do you think that if, for example, women uh behave differently, I, I mean, they express in terms of their behavior, more sexual interest or more sexual availability during ovulation, uh, should we Interpret that as a cue to fertility or as simply a cue to sexual availability or sexual interest. I mean, do you think that it would be important to establish such a distinction or not, since it happens during ovulation?

45:02 Lars Penke: Well, most directly it's an cue to sexual interest, but I think it makes good adaptive sense that it is coupled to fertility. So I think it is our old evolutionary heritage that the same hormones that Basically, uh, um, determine female reproductive functioning at the same time regulate sexual interest, and there is really good evidence all across the, uh, mammalian spectrum and even in other species that these links exist in other species, so that is really something that we share with other species, uh, very obviously. And that makes a lot of sense. Why should, uh, I mean, sexual interest as sexuality has a lot of functions in our species. We are a species with a, an extended sexuality that achieves different things with our sexual activity, but that sexually, sexual motivation should be highest at the time when it serves its most direct biological evolutionary function, namely potential conception. Uh, MAKES perfect sense, and um I, I think that's the key of the message here.

46:26 Ricardo Lopes: Mhm. OK, so when it comes to the evolution of concealed ovulation as we have in human females, I mean, and particularly since when we look at our phylogenetically closest relatives like chimpanzees and bonobos, I mean they have tras, I mean females from both species have tras. So I mean what. Uh, Among the different hypo hypotheses that people might have been putting forth, uh, recently or, yeah, I, I mean, not, not, not necessarily just recently, but that people have been suggesting, uh, ever since we've been studying, studying that topic. Uh, I, I mean, is there any one of them that you think is has most support in terms of explaining the evolution of concealed ovulation in humans?

47:29 Lars Penke: Yeah, that's a really complicated topic and one that you really need to study phylogenetically, um, and it's, it's really different, uh, difficult to, to tease, uh, different hypotheses apart in that regard. But what I often hear from my primatologist colleagues is that As far as the evidence goes, the last common ancestors of Homo and Pan, so of us and the chimpanzees and bonobos, did actually not have advertised ovulation. So it is not a question of why humans lost science to ovulation, why. Ovulation got concealed in the homo lineage, but it seems to be a question of why there was selective pressure on advertised ovulation in the palm line for the chimpanzees and the bonobos, and that has probably to do with their very promiscuous mating system. Now, I mean, there are different explanations in the literature related to parental investment and pair bonding that concealed ovulation basically. Is an evolutionary route to secure long-term pair bonding by basically making it less obvious when copulation leads to conceptions for the male so that the male needs to stick around with females for longer periods of time to ensure. To reproduce at all and actually there are phylogenetic analysis across the whole mammalian spectrum that indicate that uh concealed ovulation often precedes the evolution of pair bonding, which is rare in mammals but exists in some species. Some other analysis point towards reduction of infanticide as a very important aspect of the evolution of concealed ovulation across primate species because often males tend to kill offspring of other males so that the women become available, uh, the women, females become available for um. Um, Uh, FOR copulation and for, for reproduction earlier. Um, AND there might be some truth to the reduction of infanticide hypothesis as well. There might be some aspects of human concealed ovulation that is related to the complexity of our social groups, of our social societies, because concealed ovulation reduces. Intersexual competition both between uh males and females in the species and if you want to have large groups of, of unrelated collaborating individuals as we have in humans and as is very important for our um yeah, ability for culture and, and um division of labor and so on which are huge, huge assets in human evolution. Then concealed uh concealed ovulation is certainly an asset. Um, IT is really difficult to completely distinguish between all these hypotheses and I'm not sure if the current data, uh, completely allows that and maybe all of them, uh, uh, are true to some degree, but my perspective is that it's not so much a puzzle why Ovulation is concealed in humans, but more a question of why other species have so clearly advertised ovulation. And that, that would be evolution towards signals of fertility where there's an active evolutionary process to make uh ovulation more visible to other members of the species. What is even more discussed is if there are indirect cues of lost estros that still indicate ovulation and so on, but that would usually be something like the reddening of the face or the smell, especially of the vaginal area or so on, and. Even those kinds of cues don't really seem to exist in humans, at least there's no strong convincing evidence, and so our baseline null hypothesis uh should just be that there simply are no signs of or even cues of ovulation.

52:28 Ricardo Lopes: Mhm. OK, so, uh, uh, I, I have 3 more questions. Two of them are more general, and the last one will be more about, uh, uh, more of a theoretical question regarding evolutionary psychology more broadly. But at, at this point in time, what can we tell about the cycle shift theories then? I mean, uh what can we tell as to whether We should still take some, at least some of the predictions predictions seriously, scientifically, and to what extent they have been supported or not by the most rigorous evidence that we have.

53:19 Lars Penke: By far and large, so I, I still think it's very interesting to study these hormones across the cycle because these hormones definitely act in the whole body and they also act on the brain and It is still extremely plausible that something about the psychology changes across the cycle as well, not only the reproductive functioning and some other physiological aspects, and I think the general sexual desire, sexual motivation aspect is rather well proven. And I regard changes in self-perceived attractiveness and some behavioral tendencies that women show uh across the cycle basically as a downstream effect of that. And that I'm pretty sure about. Then, then there are other bits that have been tied to the ovulatory cycle that I think are also interesting that are not that well supported, but have reasonable support and are certainly interesting to study further. For example, James Roney uh has this hypothesis that during the second half of the ovulatory cycle, during the luteal phase. Um, UNDER the influence of progesterone, uh, appetite changes, and women tend to eat more and that, that is also an adaptive, um, mechanism that potentially prepares for pregnancy or at least for somatic investment in life history terms. Uh, I find that a rather interesting hypothesis in some of our studies, we have some evidence for that as well. I don't regard it as, as well supported as a Uh, sexual preference, uh, sexual motivation shift. But all these way more specific hypotheses. They were super interesting and they were super compelling even from a theoretical perspective, but my understanding of the literature is that by now they are. Have been so often disproven that it's not very likely that they exist. I'm not saying that it can't be that they exist at all. Some things haven't been tested at all. Some things haven't been tested very well. So if people want to, I am very open to see. New studies on this topic and if people can show that on very specific aspects there are still preference shifts or there are still uh shifts in specific aspects of sexual motivation that really point towards uh sexual attraction to non-primary partner, uh, partners when ovulating also on. I'm still open to that, but. As the literature stands right now, my. Basic tenet would be to say these effects are not there and it requires really strong good evidence to show them. That, that is my current take on the literature.

56:34 Ricardo Lopes: OK, so because the ovulatory shift hypothesis, or at least part of it, as we've already talked about here, is based on the idea or the hypothesis of good gene sexual selection in humans, what about that? Hypothesis specifically, I mean, at this point in time, what, um, how do you interpret or what, what do you have to say about the general evidence that we have for sexual selection in humans being based at least in part, of course, on good genes.

57:16 Lars Penke: So from an evolutionary genetic perspective based on the available molecular genetic and genomic evidence, it seems to be that quite a few human traits are under mutation selection balance, meaning mutations occur, mutations increase the variance in traits, and selection is part of the mechanism that. Uh Limits that this variation doesn't increase over time more and more. So there is pretty direct molecular genetic evidence that for all kinds of human traits, uh, mutation selection balance seems to operate to some degree and uh. The question is what are the mechanisms here? This has partly been taken as evidence that sexual selection plays a role here, but it could simply be that if mutations occur that are too far outside of. The standard human range that, that simply leads to uh uh uh um lethal birth, so basically to a stillbirth or that, that leads to infertility or that, that leads to uh a shortened lifespan and so on, and then that alone. Is what selects uh against this variants, but it could very well be that there's sexual selection for these traits as well, but curiously enough, it seems to encompass all kinds of human traits, not only the ones that are mostly discussed in the evolutionary literature as indicators of uh mate quality or or even uh genetic quality. Um And the other bit is that the question is in what range is a trait neutral in that regard and at which point is it really selected against and I think what is happening with the whole attractiveness literature that of course has been influenced a lot by uh evolutionary psychology. Is that we are focusing on differences between individuals that are in a range where they don't really matter. So if we have our standard student sample, which are still our white mice in psychology in terms of that it is the most studied population, it might be that in a standard student sample, phenotypic differences that might reflect. Uh, GENETIC variation are in a range where Mutational load, mutational uh incidence don't really matter. So it could be that only at the extremes of the distribution when we are really talking about limiting uh mutations that uh uh lead to uh uh limited capabilities or so on. um. That there are the differences are also so visible to other individuals that uh in one way or another, they uh affect made choice decisions. Um, THERE is an interesting uh hypothesis in the attractiveness literature called the uh overgeneralization hypothesis, and that is basically that. We are adapted to pick up certain cues and we use them to distinguish in our judgments of attractiveness and of mate quality, but When the stimulus material that we see is very limited in the range of these traits, then we try to make distinctions where these distinctions don't really have any informational value. And so we might even be able to pick up. Minuscule differences in skin quality or face symmetry or uh averageness of the face, and we might use that for our attractiveness judgments and same with all other forms of attractiveness, but. These cues only matter in the very extremes, and these extremes we usually don't even see in our samples. So, um, by far and large, I still think that. Mutations contribute a lot to genetic variants in humans and that a lot of traits in humans are under mutation selection balance, but I'm doubtful that in the samples we usually study something like made preferences or made decisions that these differences really point to differences in genetic quality.

1:02:25 Ricardo Lopes: Uh, OK, so, uh, before I ask you my last question, there's something that you mentioned there that I really want to ask you a little bit more about. So, uh, do you think that perhaps, uh, in evolutionary psychology specifically, we could talk about psychology more broadly, but do you think that The fact that there are still many studies where the sample of people are basically used are basically university students that we are not looking, we, and by we I mean people in Uh, evolutionary psychology are not looking at diverse enough samples of people to really study some of these phenomena as being part of our evolved psychology.

1:03:19 Lars Penke: Oh definitely, definitely. I mean, I don't think it is worthless to study convenient sample, but if we find something we should show that it holds more broadly. So my whole career, I always tried to at least recruit samples from the general population in studies where I could afford it in one way or another and not only the student samples that come cheap because we can give them uh course credit for participation. Um, BUT of course, even if I find something in a general population like Germany or any other country, uh, doesn't mean that I can. Immediately generalize to the whole human species, and I think, uh, anthropological work is invaluable in that regard and that we should definitely, if we propose that something is a universal human adaptation or as part of the universal adaptive design of humans, we definitely need to show that it uh exists in other samples. Um. And that is especially true for um this whole um ovulatory literature as well because if you look to natural fertility populations like small scale uh societies that anthropologists usually study. Then you see that women usually have few ovulatory cycles during their adult life because they tend to be pregnant or lactating or in some cases malnourished and uh therefore not healthy uh and therefore uh uh not ovulating so. It is actually a viable hypothesis to say in our environment of evolutionary adaptiveness. Ovulatory cycles didn't happen very often during a female lifespan, so that these very specific effects that ovulation should have these very specific conditions where um behavior then would have to make a difference in terms of fitness that they simply didn't occur often enough, so. Yes, I think the fact that basically all of the uh ovulatory shift literature has been studied in the typical Western educated, industrialized, rich and democratic societies, the weird societies, uh is a big limitation in that regard.

1:05:55 Ricardo Lopes: Mhm. Yeah, yeah, and if I may, uh, I mean, of course, anthropological, the anthropological literature is very important, and I think that collaboration with anthropologists more generally, but I think that in this case, for example, when it comes to ovulation, taking into account the, those specific circumstances where Where women might be pregnant more of the time or might suffer from malnutrition. I think that in those cases specifically, it's very important for us to also study the impact or the influence of ecological factors and perhaps look into, look into human behavioral ecology, for example.

1:06:38 Lars Penke: That's where um behavioral endocrinology becomes very interesting because I mean what hormones generally do is keep the body in balance and keep the body in balance in terms of the challenges that we are experiencing from our surroundings. So I often compare. Uh, HORMONES to emotions and that they put us in a different adaptive mode that helps us to face the challenges that we are facing right now more effectively with the end result to keep the body. Imbalance and we know that steroid hormones and ovulatory cycles are very responsive to, for example, physical condition of the body, health status, uh, nutrition status, uh, body mass index, so basically caloric status, and This is very important because the body has to decide, is it a good idea to reproduce right now or would it increase my fitness if I postpone reproduction to a later point in time, and that is why there is a phenomenon of amenorrhea, which is basically the. Stopping of the ovulatory cycle in response to these kinds of conditions, and that tells us that the ovulatory cycle is adaptively attuned in a very, Fine manner to these kinds of challenges, so there is a lot of. Evolutionarily interesting things going on with the menstrual cycle, but probably not everything that has ever been proposed in the literature.

1:08:24 Ricardo Lopes: Right. So to get into my final question then, um, how do you look at uh the general role of falsification in evolutionary psychology? I mean, uh, uh, and I'm also asking you this because Sometimes, uh, I might worry that perhaps at least when it comes to certain hypotheses like the evolutory shift hypothesis that we've explored here today, maybe, uh, Uh, some, I, I, I don't want to say all, but at least some evolutionary psychologists and perhaps the ones that are more invested in this hypothesis specifically and other hypotheses as well, um, perhaps they, they do not take falsification as seriously as they should. And I, I mean, if I may say so, sometimes perhaps there's there's a risk or they're putting themselves at risk of really being accused and there being some, at least some grain of truth to those kinds of accusation of accusations of promoting um so-called uh. Uh, I mean, just so, uh, stories are just so storytelling, storytelling when it comes to, uh, hypothesis developed by evolutionary psychologists. I mean, uh, do you agree with that and what do you think about this

1:09:57 Lars Penke: more broadly? Well, I think that the whole development of the ovulatory cycle uh literature is actually something that helped the field by showing that it is a falsifiable field. I mean, I still regard myself and I always have regard myself as an evolutionary psychologist and I have no doubt about the theory of evolution and I have no doubt that the theory of evolution is probably the most important unifying theory for the whole life sciences including psychology and psychology is a field that in general lacks theoretical support and It used to have a lot of theories that didn't really hold up like psychoanalysis, and now it is often in a theoretical void or theories are just proposed on a fly based on uh everyday life intuitions or so on, and I think that it is a huge problem of psychology in general at the moment. So I think it is really important to take evolutionary theory. Serious and to use it for hypothesis generation in psychology, but that doesn't mean that every hypothesis that is in line with evolutionary thinking. Has to be right and hypotheses have to be translated into testable predictions. We have to develop paradigms to make these predictions testable and then we should test them from all kinds of angles and of course. Individual negative studies don't disprove a prediction, but if enough evidence amounts at some point, we should say this prediction is highly unlikely and we should probably move on. And as I observe it, the field of evolutionary psychology mostly has moved on from the evolutionary, uh, from, from the ovulatory shift hypothesis. And I think it's a good thing to show. That this is an example of falsifiable evolutionary psychology. I mean, falsification basically entails that you are precise enough in terms of your predictions, your methods, your operationalization of variables, and so on, that you can run empirical tests that can be supportive or not supportive of the prediction, and that is really what has happened here, I mean. The whole debate has sparked so much uh conversations about how to really conceptualize ovulation. Do you use windows? Do you use continuous measurements? It has sparked a lot of debate about measurement of hormones. Can you really measure steroid hormones well from saliva samples? Do you need other media? Um, Is it really sufficient if you use standard immuno essays or do you uh use something like mass spectrometry, which we have been using in our studies and so on. So there has been a lot of method development, design development around this debate, and I think that was good and healthy for evolutionary psychology. And of course a hypothesis can never be completely disproven, but we are at a point. Where it looks in a way that at least some of these more complex hypotheses are unlike me and that puts out a nice challenge to people who still want to stick to these hypotheses to come forward with better designs, better tests, better samples, and so on, and I'm completely open to change my mind again, as I've done before, uh, when the evidence points in a different direction, and that is healthy for the field and it doesn't mean that. Broad ideas of sexual selection or of uh parental investment theory or of uh made choice or so are wrong as well because it is only one specific hypothesis and some very specific predictions that don't seem to be that likely anymore and I mean this. Old accusation of just so storytelling that dates back to uh Gould and Levantin was made at a time when the empirical literature was scarce and thin and didn't. Uh, STAND on, on, on very solid ground, and I think that has changed tremendously. And I don't think we are completely there. There's still quite a bit of weak research in evolutionary psychology, and I think it is still worthwhile to tidy that up and to move on to more direct evidence, for example, not only talking about good genes, but really looking at genomic evidence for mutation load and uh similar things. But, um, I think we are, are on a good path there and this was an important step in that direction. And by the way, just soul storytelling is not limited to evolutionary psychology. There's a lot of just soul storytelling and standard psychology, social psychology, developmental psychology, and so on as well, um, where These kinds of accusations haven't really sparked that much of development.

1:15:47 Ricardo Lopes: Mhm. Great. So, uh, Doctor Pinke, would you like to tell people where they can find your work on the internet?

1:15:56 Lars Penke: Yeah, well, they can just Google me. I think I'm easily Googleable. Um, uh, MY homepage is Laspeel.u but you can also find me at the University of Gotting Psychology department. Uh, OTHERWISE, I'm on all kinds of standard, uh, social networks, Blue Sky, LinkedIn, uh, X, whatever. So, if you want to get in touch, please get in touch.

1:16:22 Ricardo Lopes: OK, great. So thank you so much for taking the time to come on the show. It's been a fascinating conversation.

1:16:30 Lars Penke: Thank you very much. It was a pleasure.

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