National Geographic News
A muscular man lifts his arms.

Women rate greater shoulder-to-hip ratios as more attractive in addition to larger penises.

Photograph by Patrik Giardino, Getty Images

Christine Dell'Amore

National Geographic News

Published April 8, 2013

Bigger is better—at least when it comes to a woman's penis preferences, a new study says. The findings suggest that female choice may have driven the evolution of larger penises in humans.

Past psychology studies that have asked women about their preferences for penis size have produced mixed opinions, with some saying they don't care about the size, while others say they prefer larger penises. (Also see "Why Human Penises Lost Their Spines.")

But those women may have felt pressured to say the politically correct thing: That size doesn't matter, said study leader Brian Mautz, a biologist at the University of Ottawa, Canada.

So his team set up an experiment in which 105 Australian women—averaging 26 years old—each looked at 53 life-size images of various computer-generated male silhouettes projected onto a screen.

The gray, homogenous-looking men had different heights, shoulder-to-hip ratios (or body shapes), and flaccid-penis lengths. In past studies, women have generally perceived tall men with greater shoulder-to-hip ratios as more alluring, making these factors important in how a woman judges attractiveness.

The women in the current study were then asked to rate the men on an attractiveness scale of 1-7, with 1 being least attractive and 7 being most attractive.

Although body shape was the most important factor in whether or not women rated a male shape as attractive or not, penis size also significantly influenced attraction.

However, the relationship wasn't necessarily linear—i.e., "as you get a larger and larger penis, it doesn't necessarily mean you're getting more and more attractive," Mautz noted. (Read about the barnacle, which has the longest penis relative to body size in the animal kingdom.)

For example, the rate at which women rated the men as attractive fell when flaccid penises were longer than 2.99 inches (7.6 centimeters).

What's more, height was also a factor: "Tall guys with really large penises ended up being most attractive relative to other figures," Mautz said.

It's not totally clear why women prefer bigger penises, but studies have shown that women prefer larger sizes because they can increase sexual satisfaction, Mautz said.

The Evolving Penis

Since early humans didn't wear clothes, male penises were obvious to women. So if women chose their mates based on the size of their genitalia, it's possible that these decisions influenced the evolution of bigger penises, according to the study, which was published in the journal Proceedings of the National Academy of Sciences. (Explore an interactive of the human body.)

"We can't say for sure that female choice is what drove the evolution of penis size," but "at this point in time, penis size has an effect on attractiveness," said Mautz.

But evolutionary psychologist Gordon Gallup, Jr. said in an email that there are some limitations to the team's theory that female choice played a role in penis evolution.

For one, previous studies have shown that "the flaccid human penis is an imperfect indicator of the size of the erect penis," said Gallup, of the State University of New York at Albany, who was not involved in the study.

Theoretically, women in the early days of human evolution would have seen most penises in a flaccid state.

What's more, the results show that women paid more attention to shoulder-and-hip ratios than penis size when rating an image as attractive, he said.

Gallup has done his own research on penis evolution, which he said has been shaped by a man's competition with other males to fertilize a woman's egg.

Gallup's research has found that the penis's arrow-like shape is able to scoop rival male semen out of the female's reproductive tract. (Also see "Sperm Works Best in the Winter.")

What's more, studies using models of human genitalia have shown that deeper thrusting displaces more semen from a woman's reproductive tract than shallow thrusting. Therefore, "long penises may have also evolved to deposit semen in the deepest and more remote parts of the vagina to promote more effective sperm retention," he said.

Whatever the reason for large penises, this field of study addresses a question that some will find humorous, study leader Mautz acknowledged.

"It's important that you are serious in science, and our results are solid—but it doesn't necessarily mean you can't have fun with it."

John Peter
John Peter

I agree with you bigger is better but how we can enlarge our penis.I tell you that i was suffering this problem.My friend told me about a capsule named SIKENDER-E-AZAM PLUS.I used this capsule and my penis increased four inches.You can search it on net for getting all information.

Dwayne LaGrou
Dwayne LaGrou

Aw nuts! I forgot what I was going to say.

Ha Ha !!!

Nick Constantini
Nick Constantini

It's true, size does matter. Ask any "small" guy how it's being rejected over and over because of the penis size. I can tell that from my own experience.  If you're well endowed by the nature, be thankful. If you had 4.2" pecker like me, you'd be equally unhappy and desperate and when you're desperate you'll try anything. I tried pills, pumps and extenders, but nothing worked. Extender gave me 0.2" tho, and a hairy penis. After that, I've been reading about hand exercises performed at home, and I found a program called BuildPenis, offering week to week workouts and video explanations for each exercise, so I decided to give it a shot. I'm almost 7 months into it and I've gained almost 1.4" in length. Circumference is also bigger, not much, but for me it's a huge improvement. Sex is much better for me and my partner now. So, I'd recommend anyone who wants bigger penis, to forget about expensive pills, gadgets and methods and go straight to natural hand exercises. You won't see overnight results tho, but if you're patient and hard worker, in few months you'll see the progress. Also, you must have realistic goals. You won't get 3 inches in 4 weeks as many advertise. Hand exercises are the best method but they require time and patience, and of course good instructions.

Mike Blain
Mike Blain

As a general rule in evolution, differences between contemporary species are caused either by natural selection (in the case of any survival trait) or by mate selection (any attraction trait).  Attraction traits are very often not optimal for survival, eg. bright bird plumage makes males easier targets for predators.  More importantly they have to be hard to fake, otherwise they cannot be relied on for creating attraction, so if a bird is unhealthy or has poor genes its plumage will not be as bright.  Good example in humans is a sense of humour, you can't fake that, and that's why its a common trait we look for in a potential mate.

Penis size is a more complex attraction indicator in humans than in other primates, possibly because we are fully bipedal and its on display.  More interesting to me is the fact that humans no longer have the penis bone, which other primates have.  To speculate on why that is... it cannot be a survival advantage, otherwise all primates would have also lost it.  The bone supports an erection, but has the effect of making the flaccid penis larger as well.

Instead of actual size, could it be that the greater difference between flaccid size and erect size in humans is the real attraction trait?  The difference being more prominent when the flaccid penis is smaller, causing mate selection pressure against having a penis bone.  I would really like to see a research study on that question, though it could be difficult to do using simple images like this article described.  It could be that the attraction a woman feels is partly some pleasure that the size change is a direct response to her being present, in other words she is the stimulus that caused it.  As a man, I can't answer that.

So there's a challenge for all you psychologists out there.  How could that be measured scientifically?

Babu Ranganathan
Babu Ranganathan

All real evolution in nature is within limits. The genes already exist for micro-evolution (variations within a biological kind such as varieties of dogs, cats, horses, cows, etc.), but not for macro-evolution (variations across biological kinds such as from sea sponge to human). The unthinking environment has no ability to design or program entirely new genes. Only variations of already existing genes and traits are possible. A dog will always be a dog no matter how many varieties come into being. 

Evolutionists hope and assume that, over millions of years, random mutations (accidental changes) in the genetic code caused by radiation from the environment will produce entirely new genes for entirely new traits in species for natural selection to use, so that macro-evolution occurs.  It’s much like hoping that, if given enough time, randomly changing the sequence of letters in a cook book will turn the book into a romance novel, or a book on astronomy!
Another problem for macro-evolution is the issue of survival of the fittest. How can a partially evolved species be fit for survival? A partially evolved trait or organ that is not complete and fully functioning from the start will be a liability to a species, not a survival asset. Plants and animals in the process of macro-evolution would be unfit for survival. 

Imagine an evolving fish having part fins and part feet, with the fins evolving into feet. Where’s the survival advantage? It can't use either fins or feet efficiently. These fish exist only on automobile bumper stickers!

In fact, how could species have survived at all while their vital organs were supposedly evolving? Survival of the fittest (aka natural selection) may explain how species survive, due to minor variations and adaptations to the environment, but not how they originated. Natural selection doesn't produce biological traits or variations. It can only “select” from biological variations that are possible. The real issue is what biological variations are possible, not natural selection.

Genetic and biological similarities between species are no proof of common ancestry. Such similarities are better and more logically explained due to a common Genetic Engineer or Designer (yes, God) who designed similar functions for similar purposes in various species. Genetic information, like other forms of information, cannot arise by chance, so it's more rational to believe that DNA or genetic similarities between species are due to intelligent design.

What about "Junk" DNA? The latest science shows that "Junk DNA" isn't junk after all! It's we who were ignorant of how useful these segments of DNA really are. Recent scientific research published in scientific journals such as Nature and RNA has revealed that the "non-coding" segments of DNA are essential in regulating gene expression (i.e. how, when, and where genes are expressed in the body).
All the fossils that have been used to support human evolution have ultimately been found to be either hoaxes, non-human, or human, but not human and non-human.
All species in the fossil record and living are complete, fully-formed, and fully functional. There's no macro-evolution in nature.
Visit my newest Internet sites, THE SCIENCE SUPPORTING CREATION and WAR AMONG EVOLUTIONISTS (2nd Edition)
Babu G. Ranganathan
(B.A. Bible/Biology)

*I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I've been privileged to be recognized in the 24th edition of Marquis "Who's Who in The East" for my writings on religion and science.

Ian Murdock
Ian Murdock

Talk about bone-headed science. It is no more logical to assume that women were driven by political correctness to lie in previous surveys than it is to assume that they were socially conditioned to rate a larger penis higher. In addition, claims made in this article, such as "Bigger is better—at least when it comes to a woman's penis preferences" are gross generalizations that could be extrapolated from the survey only if ALL of the 105 women rated the figures with larger penises higher. It's simple math that said figures would be rated higher in aggregate even if only a fraction of the women showed a size preference. Do I really have to explain this to National Geographic? In trumpeting this balderdash of prurient and fanciful conclusions gleaned from a small study with untested morphology, you have done humanity a disservice.

Lara McKusky Taylor
Lara McKusky Taylor

I don't see the connection. 

Women were given silhouettes and asked to rate them on attractiveness on a scale of 1-7.  Did it specify that they were to look at the size of the penis?  Because it sounds like, from the information provided, the scientists are drawing conclusions (or rather, jumping to them).  For example, they are assuming that if a woman rated a man at a 7 and he happens to have a certain size penis, then it must be because of penis size.  When in reality, maybe he had longer hair and she liked that?  Or he was tall.  Or had broad shoulders.  Unless they specifically asked about penis size, I don't think this study is terribly accurate; the scientists are drawing a lot of conclusions here when the study parameters are not tight enough.  Furthermore, nowadays, if you haven't noticed, men ARE clothed, so penis size is not a factor in initial attraction.  Most women I know (and yes, we talk) are either intimidated by a large penis and/or find a large penis uncomfortable, especially if you're a smaller woman.  Additionally, other factors, like smile, eyes, skin and hair, which can be hugely important, were all left off.  What did they leave the subjects with?  Height, body proportion and penis size.  Huh. 

Kiara Ashanti
Kiara Ashanti

this is news to people? I thought everyone knew this/

Allie S.
Allie S.

I find it interesting that they're theorizing a female's interest in a partner was based off a male's penis size, considering many cultures - both current and non - operate with the male choosing the female, not vice versa.

I think penis size is more appropriately proportioned to work with the species' female anatomy. Looking at nature, every animal's penis size is unique to them, while most species average a certain size. Being a horse owner for many years, you notice one gelding or stallion may be better endowed than another. Horses haven't developed larger penises over the ages to win more mares..and I feel it's a pretty logical argument for humans, too - some are bigger than others, but to no real benefit; it completes the task it was designed for.

I can't say I agree evolution has caused men's penis sizes to increase. There's no reason for it, really. While we're one of few species that actually enjoys intercourse, I can't justify saying a man's penis evolved to be larger to enjoy it more. Seems a little silly to me.

Samantha Masters
Samantha Masters

I do not believe that penis size was affected by the female preference and that it affected the evolution of penises. Honestly I think it most rational to say that each penis is different and varies in size as there is still a significant number of men with small penises

Micky Harrison
Micky Harrison

@Sage RamosI tried it really works if you follow the method strictly.

Mike Blain
Mike Blain

Babu, I think the problem with your eloquent reasoning is the imprecise term "macro-evolution".  Your interpretation was... "Evolution By Big Steps", making it a whole invented concept different from real evolution.

Big steps never happen, and macro-evolution is not actually a process, it is only an "emergent property" of many many small changes.

Imagine this.  If you use very small tools for many years on a large boulder, breaking off a grain of sand with each blow, you eventually end up with a heap of sand.  Someone else (after you finished) can mistakenly suggest a special macro-process converting a boulder into a heap of sand, but in reality only the gradual chipping has ever happened.  More importantly, the actual chipping process is now invisible to the new observer.

Also, you refer to a "partly evolved" creature, which is not possible.  At any moment (including today) the genetic line is always intermediate between what it was long ago and what it will be far into the future.  Whenever you observe the gene pool it is always "fully evolved" for that specific time period, and for that specific environment. Partly evolved is a hindsight illusion.

You are perfectly correct on some points...
"unthinking environment has no ability to design", correct, and no design is even necessary for evolution to be working, today and always.
"biological similarities ... no proof of common ancestry", correct, its not proof of anything its just an observation.
"natural selection ... not a creative force", correct, it simply happens, making some individuals marginally more likely than others to survive and breed.

Regards, Mike

Crystal Witten
Crystal Witten

@Ian Murdock  I agree this is a flawed study. They seem to be making some leaps in logic, especially in the way the results have been framed. 

La Tavia
La Tavia

@Allie S. I agree with most of what you said. However there are two points I disagree with. First, the male do not simply choose the female, they compete for them. Second, on a much more important note, be careful with your use of species and variations of penis size. Yes horses and monkeys have different sizes but I am not sure how you apply that to the differences within homo sapiens. 

John Dugan
John Dugan

@Samantha Masters Size has an impact, but in the long run it's not as important as many think; the health of the tool has a greater importance long term, and that is something many men ignore. More guys should be using a quality penis health cream (health professionals recommend Man1 Man Oil) that can help address issues like dry or flaky organ skin, loss of sensation, unwanted odor, blood flow, etc.

Digital Shaman
Digital Shaman

@Mike Blain Thanks for taking the time to respond tactfully and on behalf of science!


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