Science has spoken and, yes, gentlemen, size does matter.

A newly published study by a University of Ottawa researcher has concluded penis length exerts a measurable sway on females evaluating potential sexual partners.

"We found that flaccid penis size had a significant influence on male attractiveness," concludes the study that was published Monday in the Proceedings of the National Academy of Science.

"Males with a larger penis were rated relatively more attractive."

Biologist Brian Mautz said he came to the study through curiosity over the evolution of male genitalia. Compared to other male primates, human endowment is generous.

"This observation has generated suggestions by evolutionary biologists that the comparatively larger human penis evolved under premating sexual selection," says his paper. "Novels, magazines and popular articles often allude to the existence of a relationship between penis size and sexual attractiveness or masculinity."

Nor is the effect limited to pop culture.

"Another project I was on, looking at female preferences in genital size in fish, showed that females actually do discriminate in males before copulation even begins," Mautz said. "That potentially influences genital evolution."

Previous studies have attempted to discern what women like by, for example, asking them to choose between a series of drawings of men that vary only in the size of the anatomy in question. Mautz believes those conclusions are probably limited by self-censorship.

"When you directly ask someone about a sensitive topic, you're likely to get some bias in responses," he said. "Penis size isn't supposed to matter."

His study tried to mask its intent by introducing three variations on male appearance: body shape (shoulder-to-hip ratio), height and penis size. Those variables were presented in seven gradients, small to large, and intermixed until there were 343 combinations.

Each variation was represented in a computer-generated, life-sized picture of a naked male, which could be rotated to allow an examination of the image in profile. A study group of 105 heterosexual women were then asked which picture they found most sexually attractive.

Perhaps unsurprisingly, they preferred men who were tall, long and V-shaped. Overall, body shape accounted for about 80 per cent of the variation in attractiveness scores, penis size about six per cent and height about five per cent.

"The finding suggests that selection on penis size is potentially as strong as selection on stature."

That finding was reinforced by slower response times for some pictures.

"We found a significantly positive, albeit small, correlation between penis size and response time," the study says. "This finding is consistent with a pattern in adults whereby attractive stimuli are viewed for longer periods."

That attraction, however, wasn't a simple formula of bigger is better.

"Attractiveness increases rapidly until you reach around average for each of the three traits," said Mautz. "Then, although the attractiveness continues to increase, it doesn't increase as much."

What was truly interesting was the interaction between the three traits, Mautz said.

"If you look at how penis size interacts with male height, it has a differential effect at the lower height sizes. Take the tall men — you get a really big impact (in attractiveness) of how large your penis is relative to your height.

"An increase in penis size if you're of average height does influence your attractiveness. It doesn't do quite as much as it does at the upper end of the height spectrum.

"If you're short, it doesn't matter what size your penis is."

Statistically, 185-cm tall men get about twice the boost in attractiveness that their 165-cm friends do as length increases from six to 10 cm.

If that doesn't seem fair, Mautz hastens to point out his study only considered three male traits.

Characteristics such as musculature — not to mention a pleasant smile or great hair — were not considered.

Still, he said, his results do suggest that male gentalia factor into sexual selection and are therefore subject to evolutionary pressure.

"It shows that females can exert a choice and influence genital evolution, which is a relatively understudied area."

His conclusions also have considerable intrinsic interest.

"You're my first interview," Mautz told The Canadian Press. "I'm watching emails roll into my account as we speak."

Related on HuffPost:

Loading Slideshow...
  • Average Penis Size Isn't 9 Inches

    The average size of an erect penis is about 5 to 7 inches; when it’s not erect, it measures just 1 to 4 inches. So what’s the answer to that age-old question — does size really matter? It depends on whom you’re asking. In a study of more than 52,000 men and women, which was published in the journal Psychology of Men and Masculinity, 45 per cent of men revealed that they were unsatisfied with their penis size. However, 84 per cent of women said they were completely content with the size of their partner.

  • Marathon Sex Is Not the Norm

    It’s time to cut the average guy some slack: Having sex that lasts for hours is not typical. In fact, a survey of certified sex therapists in Canada and the United States, done by Penn State University, found that the most desirable duration from penetration to orgasm is 7 to 13 minutes.

  • Guys Fake Orgasms, Too

    Do men ever bluff in the bedroom? Sure they do. A recent study in the Journal of Sexual Research found that <a href="">67 per cent of women and 28 per cent of men admitted to faking an orgasm</a> — at least once. Reasons ranged from wanting to please their partner to hoping to conceal premature ejaculation to just wanting the lovemaking to be over with already. How’d they fake it? These men reported using a combination of moaning, vocalizations, and changes in physical movements.

  • You Can Break Your Penis

    It's not easy to do — but if you’re in the middle of over-the-top, acrobatic sex (especially if the woman’s on top), you could be at risk for a penile fracture. A fracture of the penis occurs when one of the membranes surrounding a blood-filled penile chamber breaks (perhaps because a woman brings her body weight down at the wrong angle, bending the penis in such a way that causes a painful rupture). Needless to say, this causes rapid deflation of an erection and pain. And if a fractured penis is not properly treated (by calling your doctor or going to an emergency room), it can actually cause scarring, deformity, or erectile dysfunction.

  • Circumcised Or Uncircumcised? Depends Where You Live

    In the United States, the majority of males are circumcised as babies — but that’s not the case around the globe. According to the World Health Organization, only about 30 per cent of penises worldwide are circumcised. Even in America, the percentage is falling (the CDC recently reported that circumcision is slightly less common than it was a decade ago, dropping to about 57 per cent from 63 per cent). And the American Academy of Pediatrics no longer recommends routine circumcision, citing health reasons.

  • Bikes Can Be Bad for Your Sex Life

    Here’s a little-known fact: Riding a bicycle with a skinny seat can put enough pressure on a male’s anatomy that it causes erectile dysfunction. Those narrow seats may make men look like road racers, but all their body weight is riding right on the part of the pelvis that supplies blood vessels and nerves to the penis. The solution is to opt for a fat, padded seat that supports the bottom. It may not look cool, but your sex life will thank you.

  • Smoking Can Cause Erectile Dysfunction

    Just in case you need one more reason to kick your cigarette habit, consider this: Smoking has been shown to double the risk for erectile dysfunction. That's because nicotine causes blood vessels to constrict, decreasing blood flow to the penis — which can be deadly for an erection. Other studies have shown that smoking decreases the number of sperm in a man's semen and that non-smokers (who tend to be healthier overall) have a better sex life.

  • It's Not Just Down Below: Men's Brains Are Wired Differently, Too

    Research has proven what most of us have thought all along: A man's brain works differently than a woman's. Males start to fantasize about sex by age 11, and according to recent research published in the Journal of Sex Research, most men think about sex about 19 times per day (dispelling that whole “every seven seconds” rumour). Women, on the other hand, think sexy thoughts about 10 times a day.

  • Male Anatomy Has a Long Shelf Life

    Women experience a rapid loss of fertility during menopause, but men go on making sperm for decades. And while erectile dysfunction rates do increase with age (4 per cent of men in their fifties are affected by ED, 17 per cent in their 60s, and 47 per cent of those over 75, according to the National Institutes of Health), many older men are still able to get erections, enjoy sex, and even father children.