I have to confess, when I saw a global map of average penis size flying around twitter, I was like a eighth grade boy finding his first nudie magazine – I couldn’t help but take a peek. After a brief heart attack (it’s in cm, not inches), my inner scientist started asking silly questions. You know, the kind of things that would only occur to a scientist when looking at a map of penis size like, “is this just a stochastic distribution?” “is there any reason why this pattern would occur?” and of course, “does penis size even matter from an evolutionary perspective?!”
Turns out that inner scientist of mine is quite the nag. I couldn’t get through the weekend without investigating her questions a little bit, just to shut her up.
There’s no doubt that people seem to think size matters. Men certainly do. Culturally, penis length is intrinsically linked to a man’s sexual prowess and masculinity. After all, it’s entirely common to hear a man’s penis referred to as his “manhood.” Men are much more likely than women to report caring about their size. They also tend to sell themselves short compared to other men – most men who think they are small are actually average size1.
Women, on the other hand, seem to be more ambivalent. After all, less than 1/4 of women in one study reported caring about the length2. This might be partly due to the fact that women have a positively skewed view of penis length. One study, for example, found that only 6% of women thought their man’s penis was below average, while 24% thought they had a well-endowed beau1. Statistically speaking, ladies, that’s just not true. (But hey, what matters is that they’re satisfied, right? Because the vast majority of those women – 84% – are.)
Of course, what people say and what they really feel aren’t always synonymous. While many women say that’s it’s not ‘the size of the boat’ but instead ‘the motion of the ocean’ that counts, empirical studies have called them out on their bluff. For example, a study in China found that women found images of men more attractive if they were altered to have a 22%-33% increase in length3. Furthermore, the more partners a woman has had, the more likely she is to think length matters (and those with experience would know best, wouldn’t they?)4.
But is bigger really better?
Well, that is the question, now isn’t it? When I say “better”, I’m really referring to one of two possibilities: 1) that size correlates strongly to pleasure experienced by the woman or 2) that increased size enhances reproductive success for the man. The two aren’t entirely unrelated, as one might expect a highly talented man to have many willing partners. But in the latter, I’m more interested in a direct effect, as in length correlating to how much sperm is deposited, or the depth into the vagina somehow leading to higher chance of fertilization.
But first things first: does how long your schlong is matter in bed? The short answer is yes, but bigger isn’t always better. Think about it: at a certain point, you’d expect length would become… well, to put it bluntly, a big problem. After all, a woman’s vagina is only so deep. Studies tend to agree. Women almost unanimously report being able to feel the difference between men, but only 5% felt length correlated with pleasure (girth, on the other hand…)5. Furthermore, while empirical studies have found modest enhancements of length are preferred, the largest extensions were seen as less favorable3.
There’s good reason to think that penis size might matter from an evolutionary standpoint, too. After all, human males carry around a penis that is substantially larger than other primates6. There are several theories on why longer might be better. For example, it is thought that the deeper the placement of sperm, the more likely a woman is to get pregnant. There is also some postulating that a longer penis leads to increased frequency of orgasm for the woman during intercourse, which is also thought to lead to an increased likelihood of pregnancy (e.g. this, by Scicurious).
However, surprisingly scant evidence can be found which supports any theory of penis length and reproductive fitness. No study has correlated penis length with fertilization or even orgasm frequency. The only study I could find, in fact, looked at a completely different hypothesis. Gallup et al.7 attempted to determine if the human penis might function as both as a semen delivery and a semen removal device. Scicurious did a great breakdown if you’re interested, but to quickly summarize, their theory was that if a man penetrated a woman soon after another had finished, his penis would “scoop out” the semen left by the woman’s previous lover. They did find that the deeper the penetration, the more semen was displaced during simulated intercourse. However, they failed to take into account that their model penises were not representative of an uncircumcised man, and thus may not be as relevant to evolutionary history.
Really, there’s very little evidence to suggest that size matters much at all. Certainly, men who are less than the global average reproduce effectively – the rapidly expanding populations in China and India are proof of that. So what does explain the pattern of penis size across the globe?
Well, you certainly can’t rule out chance. When populations of a species are separated for a long enough amount of time, genetic changes that have nothing to do with selection accumulate – a principle which is known as genetic drift. The variation we see in penis size across the globe might simply reflect random shifts between ancestral populations.
Of course, it’s also important to note that the penis lengths reported in the global chart aren’t normalized in any way. Let’s think of a different trait – weight, for example. If I said one person weighed more than another, the first thing you’d probably wonder is if they’re the same height. Well, here’s the same world graph, but this time looking at average male height:
It’s not surprising that some of the shortest countries are short in many ways. Previous studies have found that penis size does correlate with overall height8,9. There are plenty of other environmental variables that could be in play, too. Diet, nutritional status, and many other factors affect growth of the human body in general, and could certainly affect growth ‘down there’.
It’s also important to note that the lengths weren’t all measured in the same way – some were self-reported size, which scientists have found tends to be larger than the size measured clinically1. Nor are they from the same year – it’s well established that average heights of people are shifting continually. Furthermore the weights of the men examined, whether they were from an urban or rural environment, and even the participants’ age range vary between the studies. All of these variables are correlated with penis length. Without accounting for these factors, it’s hard to compare the country averages in the first place.
All and all, while we might pass around such a map and giggle with our friends, the actual data involved aren’t that informative scientifically. We simply can’t determine if any pattern is occurring in penis length globally, and if it is, whether it is genetic drift or selection of some kind without a lot more information.
But feel free to giggle and pass it on anyway… I did!
1. Lever, J., Frederick, D., & Peplau, L. (2006). Does Size Matter? Men’s and Women’s Views on Penis Size Across the Lifespan. Psychology of Men & Masculinity, 7 (3), 129-143 DOI: 10.1037/1524-9184.108.40.206
2. Francken, A. (2002). What Importance Do Women Attribute to the Size of the Penis? European Urology, 42 (5), 426-431 DOI: 10.1016/S0302-2838(02)00396-2
3. Dixson, B., Dixson, A., Li, B., & Anderson, M. (2007). Studies of human physique and sexual attractiveness: Sexual preferences of men and women in China American Journal of Human Biology, 19 (1), 88-95 DOI: 10.1002/ajhb.20584
4. Štulhofer, A. (2006). How (Un)Important Is Penis Size for Women with Heterosexual Experience? Archives of Sexual Behavior, 35 (1), 5-6 DOI: 10.1007/s10508-006-8989-7
5. Eisenman, R. (2001). Penis size: Survey of female perceptions of sexual satisfaction BMC Women’s Health, 1 (1) DOI: 10.1186/1472-6874-1-1
6. Small, Meredith F. (1995). What’s Love Got to Do With It? The Evolution of Human Mating. Anchor Books. ISBN 0385477023.
7. Gallup, G. (2003). The human penis as a semen displacement device Evolution and Human Behavior, 24 (4), 277-289 DOI: 10.1016/S1090-5138(03)00016-3
8. Edwards, R. (1998). The deﬁnitive penis size survey
results (6th ed.). Retrieved March 27, 2010, from
9. Ponchietti R, Mondaini N, Bonafè M, Di Loro F, Biscioni S, & Masieri L (2001). Penile length and circumference: a study on 3,300 young Italian males. European urology, 39 (2), 183-6 PMID: 11223678