https://youtubetranscript.com/?v=egiaqRh2Js4
You did some work on the perception of attractiveness, bilateral symmetry, averageness, and sexual selection. Can you outline what you found and why? Yes, I did work some years ago now in human attractiveness, and that turned out to be very productive about attractiveness in general in animals. One of the key traits that animals look at in judging physical attractiveness of partners, of mates, is bilateral symmetry. A colleague and I in the early 90s came up with a way to measure facial symmetry in humans. It had been worked on before, but the measurements that they used didn’t work, so we came up with a method that did work measuring bilateral symmetry in the face. So that is the symmetry of the two sides of the face. Why is that important and why is it a marker for attractiveness? It turns out that bilateral symmetry is a measure of developmental health, and so the organism, when it starts developing, it’s designed by evolution, by selection, to achieve a bilaterally symmetric form. You can think of that, this is the case, when I say organisms, I mean all forward-moving organisms. All forward-moving organisms have adaptations, developmental adaptations, to achieve a bilaterally symmetric body, because first of all, that reduces drag. So if you’re moving forward and you’re bilaterally symmetric, you don’t have any drag in your movement. You can think about a person with a leg a bit shorter than the other, and there’s drag in the forward movement. The more of that asymmetry, the more drag. So you lose efficiency and movement. That’s fundamental to what bilateral symmetry is about. But next, bilateral symmetry is very hard, perfect bilateral symmetry is very hard to achieve by development. So it’s a marker of quality of the individual pertaining to its developmental health. We see in many things that human beings design to move forward bilateral symmetry. Cars or automobiles are bilaterally symmetrical, airplanes are bilaterally symmetrical. So we like our world to be that way. Yeah, we like to be that way actually, it turns out. And well, we’re associating it with the same principle. If you had one side of the car asymmetric compared to the other side of the car, then there’d be more drag. It’s not an efficient, you’d use more gas. Think about it that way, in driving down the road with an asymmetric car. But so this is one component of physical attractiveness, bilateral symmetry. And we looked first, we developed this way to measure facial symmetry. That became a very hot research topic. We did the first and then others followed very quickly. Lots and lots of research has been done now. But there’s symmetry of movement that’s important in how fluid one’s movement is. And how attractive therefore one’s movement is. You’re not dragging your foot or whatever. And all that is really a component of the importance of health in physical attractiveness. So physical attractiveness fundamentally is a health certification. That’s how we judge people’s attractiveness. We don’t think about it consciously. It’s an unconscious calculation of the traits important in health. And developmental health as bilateral symmetry is one of these. So you measure the symmetry of the two sides of the face. And we showed in our first study of this way back now, that that measurement relates to how attractive faces are perceived. Try faces of the same sex or opposite sex. And then that research went on to look at kids looking at faces and different ethnic groups looking at faces. It works like a charm wherever you do it. Lots and lots of research. And so does it mean that if you show people symmetrical or asymmetrical faces that they obviously have a preference for the symmetrical faces? Will they look longer at the symmetrical faces? Will infants look longer at symmetrical faces? Yes they do. Yeah, that’s the way the infant beauty research is done. You just look at whether the baby, and they got it down now to almost newborns, you know, looking at faces and judging these faces basically on the basis of interest, how long they look at the face versus getting distracted to something else. And symmetry is one part of the beauty, whether you’re talking about babies or kids or old people or young people or whatever, facial symmetry is very important. It’s not the only beauty marker in the face we look at. We can talk about that in a moment too because that gets us into some other research we’ve done. But symmetry is a very important one. That research went on to look at how symmetry plays out in the everyday lives of people. And we did the initial studies on that, but again that research boomed and lots of people have done it and still it’s an active part of research. But the first thing we did, not just attractiveness, we did a bunch of that in relation to symmetry, but we looked at sex lives of people, romantically paired people, studies of couples and looked at reports by men and women of sex partner numbers they’ve had in their lifetime. That was one component of them because that’s a measure in men in particular of what biologists call mating success. So a number of sexual partners one has. And that research showed that for men, the more symmetric the man, the more sex partners he had. And a technical tale there, after we initially started with facial symmetry, but then we moved to the body of people. We came up with a metric for body symmetry measuring 11 traits on both sides of the body. These traits are ear length and ear width. And then we measure elbow, there’s an elbow anatomy there that we measure, some bones, wrists, fingers, all those men measure of course on both sides, measure foot width, ankle width, traits like that. And we put that together in a composite as a measure of body bilateral symmetry. That correlates highly with facial symmetry because the symmetry is a developmental health measure throughout the body. And that correlates with mating success of men. More symmetric men are physically more attractive and they have more sex partners. We also got into looking at men’s infidelities in their relationships and found that more symmetric men engage in more matings outside the pair bond as well. So that’s part of their mating success. We did the first study of kind of modern study, we would call it, of female orgasm in copulatory orgasm. So in part looking at women, 200 romantically paired couples and asking the women about their orgasm patterns during mating with their partner and separately asking the men. And we found that the men’s reports and the women’s reports of frequency of copulatory orgasm by the women were very highly correlated. So men are paying attention to this phenomenon of whether the female is sexually aroused to the zenith level of orgasm of course. And more symmetric men were firing more copulatory orgasms too. That was a very classic study in human sex. So I have a specific question about that. I’ve always wanted to ask a biologist interested in sexual behavior but I know that there’s been a lot of discussion about the hypothetical evolutionary purpose of female orgasm. And I was wondering if female orgasm is disproportionately likely to trigger male orgasm? Because it could be an adaptation that’s used to elicit pregnancy essentially. Yeah, I don’t think it is. There’s no evidence that females that orgasm very infrequently have fewer babies. And actually women who don’t ever orgasm can be quite fertile. So I don’t think it’s fundamentally that. I think what it is, is it’s part of female mate choice and more basically sire choice of the female. Let me explain. So when a female has an orgasm, she has uterine contraction of course. And that pull, it works like a suction. It pulls the content of the vagina up to the cervix. So it puts the content of the vagina in a good place. And if that content includes the male’s ejaculate, then she’s pulling the male’s ejaculate up to the cervix where it’s easier for him to get, you know, easier for the ejaculate to get into the right place to conceive. So if she, imagine a female who has two mating partners, she orgasms with one, pulling his ejaculate up to the cervix. And she skips orgasm with the other partner. So she in effect is mated with both men. So that is, you know, same mating success of the two men, if you just look at mating success. But she’s doing something more subtle that is differentially affecting the fertilizing capacity of the ejaculate of the two men. The ejaculate she pulls up has more potential for fertilization. And that’s a component of cryptic female choice. So in the 80s, I discovered what I labeled as cryptic female choice first in insects. And then it applied to female orgasm too in humans. As cryptic female choice is just the kind of female choice that is invisible if you’re only measuring mating success. So in the example we talked about, the two guys mating with this female had the same mating success they both mated with. But one was preferred over the other by the female’s orgasmic capacity with him that pulled his ejaculate up.