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.


  1. men have nipples because in fetal development, the default body type is female. Until around the 4th or 5th month of gestation when the mother’s body delivers an “androgen wash” which triggers the development of male genitalia. If the XY baby is deprived of that androgen wash, they continue to develop as females in body type yet still with XY. Women have orgasms to make sex desirable to them. why would they pursue sex EVER if there was nothing in it for them. God is smart

    1. ANNJET, Exactly — in addition to which I subscribe to the theory that the “necessary” social body parts are the parts that change, because it depends on the selection by the oposite sex. Zulu men are tall because the Zulu women prefered tall men. period. I happen to like smaller women with smaller nipples. Other men are exactly the oposite. Seems to me un-necessary external body parts are equal – because the other sex doesn’t care. I lived in west China for a while, the women have small feet (not from binding) because the men like small feet. Seems these researchers prefer to be precicely wrong than more or less correct.– waste of money.

    2. NO it is not. There is no such thing as “default” in embryonic development. If that were so, the default would produce humans incapable of sexual reproduction; nature is not that stupid.

      If the embryo is XY to begin with it undergoes androgynous development until certain triggers kick in, based on the presence of the X chromosome.

      You offer unsupported assertion about an “androgen wash”; where does this term appear in the literature?

      1. you’re a moron dude – the Primal blueprint is X… all mammalian fetuses begin life with FEMALE genitalia – and when a few months old the XY fetus begins the androgen-wash when the outer labia grow longer and fuse down the middle creating the scrotum (pull down your pants and you can SEE where they fused if you’re not too obese in addition to being obtuse)… the developing ovaries become the testes, and the developing clitoris grows longer and becomes the penis… basic high school biology you apparently didn’t get when you dropped out…

  2. Orgasms are the incentive nature installed to move humans into procreative behavior and thus applies to both sexes.

  3. I wonder whether the authors considered male sexual proclivities for nipple size. Perhaps different men are attracted to different nipple sizes. Thus, men who monopolize women will be attracted to a specific female nipple shape, thereby greater opportunities for the women with the non-preferred nipple size.

    Consider nipple size as a genetic adaptation of women to have a greater gene pool to select from.

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