UNM Connections; 206; Science of Sex Appeal

. . . . Hello and welcome to UNM Connections. I'm Valerie Santiannis. UNM biologists are trying to understand what it is that makes us attractive to the opposite sex. Using studies in body and facial symmetry, these researchers have some biological and evolutionary theories about how humans choose their make. Joining us to talk about their controversial and interesting work on the science of sex appeal are ecologist Randy Thornhill and Steve Gangstead of the UNM Biology Department. All coming up next on UNM Connections.

. Hi Randy and welcome to the show. Randy I understand that you have a theory about attraction and attractiveness. What is that theory? Our theory of attraction and attractiveness is a biological or evolutionary theory of how attractiveness has come to be, how beauty has come to be, physical beauty, and how our perception and evaluation and judgment of beauty has also come to be. And an evolutionary approach to these issues focuses on the ancient selective pressures in the evolutionary history of our species that has produced beauty on the one hand and the preference for beauty on the other.

Randy why have you focused on symmetry as a central theory of attractiveness? There are three main characteristics that define physical attractiveness. Age is one, symmetry is another, and what we call the hormone markers is a third. And these three components of physical attractiveness have all evolved because they are markers of an individual's health. And in our evolutionary history individuals who preferred markers of health on the body would have obtained mates with high survivorship, that is healthy mates will survive longer, and will have obtained mates with high genetic quality, resulting in the offspring with those mates that will survive. So how does facial and body symmetry denote health? How is that a more important health?

Well the three characteristics of beauty, age, symmetry, and the hormone markers each relate to health in the following ways. Age is an indicator of health because as we age we senes, our body begins to fall apart. So all else equal, youth is associated with greater health. And so a preference for young mates, and this is especially a preference that men show, but it's a preference that both sexes show to an important extent. All else equal, both sexes like young partners, young mates. So with regard to the hormone markers, the hormone markers that are important in our beauty judgments are indicators of hormonal health, specifically the reproductive hormones. And thus our preference for them is a preference for reproductively healthy mates and mates that will survive long, that will produce offspring that are reproductively healthy.

The preference for symmetry is specifically a preference for developmental health, and animals that are bilaterally symmetric, that is, roughly the same on both sides of the body, during their development there are two categories of things that disrupt that development and create asymmetry in normally bilaterally symmetric traits. And these two categories of things are environmental insults, various sorts, disease organisms can throw off the development of symmetry, toxins in the environment can throw off the development of symmetry, and food quality, food quantity, all these environmental insults, disrupt development leading to asymmetry. The second major category of factors affecting the development of asymmetry are bad genes, we all possess mutations to varying degrees, but these mutations throw off development leading to asymmetry.

The preference for a symmetric mate is indeed a preference for an individual that is developmentally healthy, specifically developmentally healthy in terms of ability to achieve bilateral symmetry in the body. The preference for a symmetric mate is a preference for an individual who has relatively few of these development disrupting genes, and an individual who is succeeded in dealing effectively with environmental insults during development, so it makes a lot of sense for animals to use symmetry in mate choice. We measure a number of body traits, and we measure these traits on both sides. We measure the ears, measure ear length and ear width, we measure elbows, we measure wrists, fingers, ankles, and feet.

Each of these traits is measured on both sides, and from the measures on both sides we can get an asymmetry, a difference in size on the two sides. We can find these traits into an index that gives us a measure of the individual's developmental stability as we call it, which reflects the individual's developmental health. So how does symmetry affect human behavior? In humans, symmetry of the face, symmetry of the body are related to various kinds of performance, and we've done a lot of work on facial symmetry, and there we analyze the symmetry of the face. We look at the relationship between facial symmetry and attractiveness ratings over the face. So facial symmetry relates positively to attractiveness of the face, so symmetric people are more attractive. Does this mean that someone who has a crooked smile is going to be seen as less attractive than someone whose smile exactly matches up on either side of the face?

Any facial expression actually creates some asymmetry in the face, and that's somewhat different. The expressive asymmetry in the face is different than this kind of asymmetry that is a marker of developmental health. Crooked smiles probably indicate more about the individual is not genuinely concerned about another. It's kind of a fake smile more than an indicator of lack of developmental health. But the symmetry in humans relates to performance in various areas of health, for example. Many, many studies have looked at the relationship between developmental stability of the body, basically symmetry of the body, and mental health. And these studies show that individuals who are relatively asymmetric have more mental health problems, and these problems range from attention deficit disorder and hyperactivity in children and those kinds of problems to actually mental retardation.

So symmetry is related to mental health in humans, and we've done studies of UNM undergraduates, a couple of studies looking at the relationship between symmetry and IQ. So this is in normal students, not I mean normal humans, not clinical populations of mental patients, and we find that more symmetric men and women have scored higher on standard IQ tests. And this is what we expect, because symmetry on the outside, so you measure the body symmetry of these subjects. And symmetry on the outside we anticipated in this study would be a marker of developmental health on the inside, so developmental stability on the inside, including in the nervous system itself. And that is implied in our results on the relationship between body symmetry and higher IQ. So individuals that are developmentally stable on the outside, which we can measure as body symmetry, are developmentally stable in the nervous system, which gives higher IQ, it gives more studies indicate more emotional stability and so forth.

And it really is more than skin deep. Absolutely, it goes all the way to the core of the individual and across the nervous system, how well the brain functions, and IQ and emotional stability, we think our markers that we pay a lot of attention to, in assessment of others, obviously we do pay much attention to IQ and emotional stability and so forth. But there are actual markers of the developmental integrity of the nervous system itself, and that's why we have evolved to pay attention to these features. I'm placing points on the face, and from these points we can determine facial symmetry, and we can determine the hormone markers, the size of the hormone markers in human faces, and symmetry and the hormone markers are both of interest to us because they're both involved in our beauty judgments.

We place points on the face, as I'm doing here, corresponding points on the two sides of the face, this is for her cheekbones, the nose, edges of the mouth, inner eye points, outer eye points, chin, and from these we can determine the size of the hormone markers as well as the symmetry of the face. To study symmetry, we use a series of lines across the face represented here by this technique, and these lines connect the corresponding points on the two sides of the face. And then we calculate the midpoint of each of these lines, and on a perfectly symmetric face, all the midpoints will lie on the same vertical line. We subtract the midpoints, and that's our measure of facial asymmetry.

We have found that symmetry in men is related to many aspects of men's sexual behavior, and symmetry in men, body symmetry in men is correlated with men's aspects of men's sex lines, basically. So that symmetric men begin sexual behavior earlier in their life history, so they lose virginity earlier, symmetric men have more sex partners in a lifetime. Symmetric men also stimulate more orgasms in their mates, specifically during mating. So our studies of romantically involved couples, these studies I'm describing now, cut across over a thousand research subjects, and our studies of romantically involved couples involve 200 romantically involved couples. And so we ask these people, we ask the man and the woman in the couple about the orgasmic behavior of the female during copulation, frequency of orgasm, we ask the man and the woman, the woman gives a report, the man gives a report.

And then we combine these reports, and that gives us an estimate of the female's orgasmic frequency during copulation. And we find that more symmetric men stimulate more copulatory orgasms, and this is of interest to us, because other research indicates that female orgasm is an adaptation that pulls sperm from the vagina to the cervix. And thus puts it in a place where it has more fertilization potential. And so if a woman orgasms with one male, but not another, say a woman in a multiple male mating situation, she has two sexual partners, if she orgasms with one male, but not the other, then she would be saving the sperm of the male that she orgasms with, but not the sperm of the male that she does an orgasm with. So it's like a mate choice mechanism, basically, or a sire choice mechanism, as we call it. She's mating with both males, but she's behaving through orgasm in a way that differentially favors this sperm of symmetric males.

So this is how she may choose who she has children with. That's right. This is one of the ways. How does this theory apply to species other than humans? In many species now, probably close to a hundred have been looked at across birds, across insects, fish, mammals other than humans, and so forth. These species that have been looked at by biologists, especially in the last ten years since this symmetry phenomenon has been discovered. And biological research is focused on looking at the relationship between symmetry of animals' bodies and various performance variables like survivorship, like mating success, like attractiveness to the opposite sex. And these studies have been reviewed recently by myself. And in general, in many, many, many species, you get the relationship between symmetry and attractiveness to the opposite sex.

Also, in many species, symmetry is related to growth rate of the individual, so symmetric offspring, growth faster, symmetric individuals of both sex is survive better, and so forth. Randy, thank you so much for joining us today. This is a fascinating subject, and we sure appreciate your being here. Thanks. Hi, my name is Melissa Franklin. I'm a researcher here at the UNM Biology Department, and we're currently doing research on facial perception. We're using a computer program that morphs from a hypermale to a hyperfemale face, and seeing how these features are perceived by different people. We're finding that the most extreme dimorphic features, that is the most extremely feminine face, has been perceived as the most attractive and most appealing face to all people. And what we're trying to determine now is why the most masculine face is not perceived all the time as the most appealing face.

And determining why the most extreme masculine features are not always perceived as the most physically appealing may give us a clue into whether people are perceiving these features as health cues, or whether they're perceiving these features as cues of personality, or finding that women at different points in their menstrual cycle, for example, when their most fertile, prefer the most masculine faces, but women in the nonfertil part of their menstrual cycle do not prefer the most masculine faces. With me in the studio now is Steve Gangstedt. Steve, welcome to the show. Thanks. So Steve, we've learned that it's very possible that men with the most symmetrical features have the best luck when it comes to mating. What kind of mates do these men make? Well, we've looked at that in study of college students and their romantic partners. What we did is we had men and women come in together and fill out questionnaires on each other in separate rooms.

And what we found is that the symmetrical men actually don't make perfect mates across the board. They seem to be more preferred because they're health, but in fact, they're partners and then report that they're less honest to their partners. They sexualize other women more. They have more romantic relationships behind their partner's backs, and they are less giving of time. There are some benefits that they seem to give. They're seen as being able to provide more physical protection, but not more willing to. So overall, it seems that there is a trade-off that comes with these partners that they do give certain benefits, but they're not across the board better mates. So why do you think that that is something that hasn't been taken out of our systems that desire or that need for this symmetrical man? You would think that with being able to intellectualize and say, here's what I want compared to, here's what my biology is telling me I want, why haven't we been able to separate those?

Well, I think overall, again, there's sort of a trade-off. Yes, there are certain downsides to being with symmetrical men, but then we once again have to remember the upsides. Presumably, these men, again, are healthier even though these are very subtle signs of health. They may give better genes to the offspring of their own offspring and their mates offspring. And those benefits may offset the downsides in the actual material benefits and support they give to their partners. Now, you've also done some research on the role scent plays in how we choose our partners. Can you tell us a little bit about that?

Yeah, we've looked at how the preferences of a scent that women have. And it's interesting to look at women in particular because it turns out that women claim that scent makes a bigger difference to their own sex desire than it does for men. What we've done is we've had men come in and they wear t-shirts for two consecutive nights and they bring the t-shirts back. Women come in that day on the next day, smell the t-shirts in bags, and what we do is we look at the relationship between the women's ratings and the symmetry of the men. So, the women are smelling these shirts and then saying, I like this one. They're rating them on two dimensions. One is pleasantness and one of them is sexiness. And that's put together into an overall attractiveness rating. So, those are two different things. Pleasant odor, sexy odor.

Yeah, it turns out, however, that with these shirts at least are highly related. They almost perfectly correlate. Now, do you find that some women find one smell very sexy and another woman would not find this sexy? Well, there are some differences across women. There's not perfect correlation between women's ratings. Overall, however, there is some positive correlation. So, women tend to agree on what are the sexy shirts and what are the least sexy shirts. So, what makes it sexy? What's going on there? Well, we don't exactly know. I mean, what we have looked at with regard to symmetry is we've looked at the relationship between symmetry and the ratings. So, what we find is that women prefer the scent of the symmetrical men, but there's an interesting detail. They prefer it only near ovulation. They have no preference for it in the luteal phase, which is after ovulation where there's really no chance that they could become pregnant. They also have no preference for it very early in the menstrual cycle when they have really very little chance of getting pregnant.

So, it's only when there's a conception risk that they have a preference for the scent of the symmetrical men. That's fascinating. That's great. Well, we think that this relates to your previous line of questioning with regard to the benefits and the downsides of being with symmetrical men. The downsides, again, is that they don't give as much support and care. However, the upsides is that potentially they can give genetic benefits to offspring. And we think that, ancestrally, women were selected to particularly prefer men for their genetic benefits, and hence particularly prefer them during these days in which there's conceptual risk. So, there's no particular benefit or outside of, at least in terms of genetic benefits, outside of those days of conception risk. Now, you've also been doing some research in the West Indies. What have you been working on there? Well, we've been working on an island called Dominica, which is a very mountainous island there. It's not really well developed.

We've been working in a small village or a rural village there. There's a road that that ends in this village, but I think that it was paved just in the last decade. And really, this is a pretty remote village. What we've been doing is looking in that village, whether we find the same sort of relationships between symmetry and men's partner number. And attractiveness as we find in the U.S. in a college sample. Does doing the research there take out the factors of the urban environment and education? It's a very rural environment there. Now, they do have fairly reasonable education and so on. Not many of these people are going on the college, but they do generally go through high school. But it certainly is a place where they get much less exposure to western ideals of attractiveness and the media and so on.

They do see some of it. The anthropologists we work with brought down a VCR and so they see some movies and so on, but overall pretty limited exposure. So, do we see a big difference between the way people make there and the way people make in the U.S.? Well, we haven't found a whole lot of difference. What we found is that, as with here, the more symmetrical men are claimed to have more partners. Now, here we didn't use a self-report. We used reports of other villagers, basically, ratings. It's part of what's known through the gossip network, but also what would be acknowledged by the people themselves in terms of what partners they have and so on. And there's pretty good agreement between our Raiders, so we can trust our information pretty well. And once again, the symmetrical men are particularly, they have the largest number of partners. Interestingly, there we also asked about how good a partner they'd be as an investing mate, as a marriage mate.

And it's interesting. There, they often don't marriage or marry immediately. They will, oftentimes, women will have a child or two without being married to the man. So marriage really, I mean, it means something, sometimes it comes quite late in a woman's reproductive career and so on. But there, the symmetrical men are somewhat preferred as investing mates, but the relationship is not nearly so strong as with partner number. We think that once this is sort of similar to the findings we find here, where men, the symmetrical men, have a lot of partners, but in fact, they don't necessarily make the best investing mates. So what should women out there watching this show take away from this research? Well, I'm not, I think they can probably get some insight into their own behavior, but in fact, really part of what we're looking at is sort of the wisdom that our evolution has given us, even if we don't necessarily think that it's wise and gets us into trouble. So in fact, it's more women can sort of reflect upon their own reactions and so on. I don't know that they'll necessarily, they may understand them better, whether or not they actually affect their choices.

They actually affect their choices, I don't know. Okay, that was really great. Thank you so much, Steve. We sure appreciate you're coming out to the show. Music Music Music

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