Nipple Size Study Challenges Theory On How Our Bodies Have Evolved

NEW YORK — The human nipple may be an anomaly when it comes to evolution. Researchers have long theorized that organs and body parts which show little variation in size stayed that way through time because they serve specific purposes. But a new study that examines nipples of both men and women proves that theory wrong — because nipple size varies significantly on women, but not men.

Whether it’s debating if women should be allowed to walk around topless legally like men or simply putting thought to the age-old question of why men have them to begin with, nipples have long been a controversial and, for many, awkward topic. Of course, they do come many shapes and sizes, so researchers from the University of Queensland in Australia sought to better understand whether nipple size actually served any significance. The male nipple has been decidedly viewed as an evolutionary byproduct — a useless version of the female nipple, which is highly functional and serves a great importance after birth.

Shirtless man
A new study that examines nipples of both men and women proves a theory of evolutionary biology wrong — because nipple size varies significantly on women, but not men.

What they learned calls into question years of prior research when it comes to evolutionary biology. Experts say the field serves to determine how the body has changed — or remain unchanged — to adapt to conditions throughout history. Physical features that are similar between beings have likely remained unchanged because of the importance of their functionality, scientists have argued. Or they’re the result of strong evolutionary selection. Conversely, features that appear one way on a body and completely different on others must serve little purpose and result from weak evolutionary selection.

The authors specifically point to a 2008 study in the journal Evolution & Development that concluded the female orgasm was a “functionless developmental byproduct of the functional male orgasm” — because the female clitoris was found to have greater variation in length among women compared to penis size among men.

But this new study, led by Ashleigh Kelly, a researcher at the university, throws a wrench into that theory. Kelly and her team studied the nipples of 33 men and 30 women enrolled at the university, scanning the participants’ chests and taking nipple measurements. They also took measurements of the individuals’ height and chest circumference.


Researchers found that male nipples tended to be mostly uniform between men and were on average about 36 percent the size of the female nipple. Women on the other hand, tended to have greater variation in their nipple area size. They found these results to be true even when things like height, weight, bust size or chest circumference were taken into account.

“We found that female nipples were significantly more variable than male nipples,” Kelly says in a release. “Female nipples are functional as they are used in breastfeeding. Therefore, the finding that females nipples are highly variable discredits previous studies that indicate variation in a specific feature indicates a lack of functionality.”

Their findings, they say, should lead scientists to disregard the earlier study that concluded the female orgasm evolved for no other reason than the fact that men have them too.

The study by Kelly and her research team was published in the journal Adaptive Human Behavior and Physiology.