 Hi, my name is Michael Jenians and I'm from the Australian National University and today I'm going to tell you in 10 minutes or so about a study we've done looking at the effect of human penis size on male attractiveness. Now this study was led by Dr. Brian Moutz, who is a former PhD student in my group. So modern Western culture is obsessed with penis size. You don't have to go very far to discover this. If you go down to your local news agent and look at Cosmopolitan, you'll soon discover articles asking, does size matter? Is a larger penis better than a smaller one? And if you go to the men's side of things, you'll see an obsession with penis size, which is reflected in jokes and the way males interact with each other, which seems to imply that penis size is a highly advantageous character and with a larger penis is better. But there's a little bit of a contradiction between the two. There's emphasis on large penis size. And at the same time, studies saying maybe penis size doesn't matter. For example, maybe having kind eyes or a good sense of humor is more important. So what is the truth? What is the reality? Does penis size matter or not? Now, this is not just a question that obsesses modern Western society. It's been part of many cultures and for a long time. So for example, if we look at medieval times, we have a feature such as cod pieces, which are clearly designed to emphasize this part of the male anatomy. Similarly, across cultures, here we have a gentleman from New Guinea wearing a penis cord rather optimistic looking. So this interest in penis size has been around for quite a while and spans a range of cultures. It's also a valid scientific question. So reputable scientists such as Jared Diamond and Geoffrey Miller, bestselling authors and as I say, reputable scientists have asked, why is penis size so large in humans relative to other primates? So for our body size, we appear to have a large of an expected penis size. Why is that? Well, we wanted to answer this question scientifically using an objective method. We wanted to try and get around all the problems with questionnaires. Questionnaires have problems because people lie or unintentionally lie because they self-deceive. So we wanted a more objective way to reach the answer. So what Brian, my colleague, did is to create a whole bunch of male humanoid figures, a bunch of naked guys, computer animations, and these varied in three parameters. Height, how tall they were, body shape, which was basically the shoulder to hip ratio going from V shaped to pair shaped and crucially in penis size. Now the range of values we use, these seven values for each character, was such that 95% of men in the standard Western sample would fall within this range. So we didn't go to the absolute extremes, but most men are covered by this range. And one thing I want to emphasize to you here is that we know from previous studies that body shape is important, females generally prefer V shaped men, broader shouldered, and height matters, females generally prefer taller men. So that allows us to calibrate and say, well, in that context, how important is penis size? We need some kind of benchmark. Now here you can see the extremes of the figures that were generated. So the figure over there on the far side is the most pair shaped, the shortest with the smallest penis. The individual here on the right is the tallest, the most broad-shouldered, narrow-hipped with the largest penis. So those are the extremes. Now these figures were presented at life size to the subjects, and in addition, we arranged for them to move like that. And as you can see, that's in a fairly subtle way, increases the ability of the subjects to perceive the penis size as the individual moves around. Okay, so how did we collect the data? Well, we asked 105 women to view full life-size video images. We thought it was important they were fully life-sized because your response to size properties, whether someone's tall or short, for example, whether a penis is large or small, is quite a visceral response. If you look up, you know someone's tall. If you look down, you know that they're short. And that could give a very different answer than to the more traditional approach of simply asking women to assess figures that are presented on a piece of paper or maybe on a small computer screen. All right. We then asked the women to rank these characters from one to seven for their attractiveness as sexual partners. The women responded very quickly. On average, it took them about three seconds to respond to each video they saw. They saw the video sequentially one at a time, three seconds. Now, to give you an analogy, imagine if you wanted to buy a house and you were interested in three properties of the house. How big it was, how many bedrooms, how much money it cost, and how far it was from the city center. And I presented you with a whole bunch of houses that varied for these three parameters and gave you three seconds to choose. It will be difficult for you to consciously single out any specific character. But overall, the decision you made as to which house was most desirable would eventually reflect the relative importance you placed on these different characters. And effectively, that's what we've done in this study. We then used a standard evolutionary selection analysis to analyze the results. I won't say any more about that except that it's uncontroversial and is used for all kinds of studies of other animals. I'm a biologist myself. I don't usually work on humans. And we use this approach in crickets and fish and many other animals. We wanted to apply it to humans. So what traits mattered? Well, firstly, we found there was linear or directional selection on body shape. It explained about 80% of the variation in how attractive a figure was. Linear selection simply means the bigger's better. So females preferred a more V-shaped male. That fits with our previous result, but with previous studies, that's great. Secondly, height was also a significant, highly significant predictor of attractiveness. Again, that fits with what we've known previously that taller men are more attractive. Finally, the bit you've been waiting for, I hope, penis size. It also was under linear directional selection. A larger penis was more attractive. But what I want to emphasize is that height and penis size were equally important. And that was, to be honest, a somewhat unexpected result because we know that height is very important and yet height and penis size had an equally strong effect in our study. So your next question is, well, how big is best? Funnily enough, we don't actually know the answer. Why is that? Well, it turns out that the most attractive penis size was not in our test range. Penis size increasing here, attractiveness score going up there. You can see small penis unattractive, attractiveness increases with penis size and starts to diminish over some sort of non-linear effect. It starts plateauing out. But we never actually reach the peak because we don't see a decline. We don't see a penis size that's too large that it becomes unattractive. So the simple summary of that would be the most attractive penis size is outside our test range, which means it's larger than that found in 95% of men. Another little interesting fact is that we found that females took a far shorter time to rank males with a smaller than large penis. Again, they weren't consciously doing this. It simply happened. Simply put, a small penis, females very quickly said no unattractive and moved on to the next figure. Now, in this final little bit, I want to simply summarize the relationship between the characters, how interactions between different characters affect each other. And what you have here on the x-axis is the height. Short individual, tall individual. On the y-axis penis size, small penis, large penis. You can think of this map like a contour map that you would use when you go hiking. And it's joining up. Lines are joining up values that have the same level attractiveness. Red is high ground. Red is sexy. So the redder the coloration at a point, the more attractive. So for example here, a very tall individual with a very large penis is the most attractive. Conversely, a short individual with a small penis is the least attractive, blue unattractive. Now what I want you to notice here, however, is the interaction between the characters. If you look at a short individual, simply and bluntly put, no matter how much the penis size increased, there was very little change in their attractiveness. They remained blue and crossed fairly few contour lines as though staying on flat ground, flat low ground. In contrast, for a tall individual, as penis size increased, they crossed many contour lines, going up a hill, heading to higher ground, more attractive, redder. So in sum, there's an interaction such that penis size matters more for a tall male than it does for a short male. And we found exactly the same thing when it came to body size, or body shape, should I say, the V shaped pair shaped has a very similar relationship. So just to summarize what we found, some of our results support previous studies. For example, the taller men are more attractive. Similarly, the broader shoulders and narrow hips are more attractive. That's great. It means that our method that we used works. What about our new results? Well, we showed this diminishing returns on higher values. It's not simply the case that an ever-increasing V-shapedness is better. There's clearly diminishing returns, although we don't know where the peaks lie. Also, we showed that traits interact. You can't look at a single trait in isolation. You need to consider the interactions between them, as I just showed you, between penis size and height. And finally, and perhaps most importantly, we've been able to answer the age-old question. Penis size does matter, no matter what they say. Thank you for listening. Goodbye.