What nipple size means for evolutionary biology

June 26, 2018, Springer

Nipple size varies markedly from woman to woman, whereas male nipples are more uniform. This finding goes against a common assumption of evolutionary biology, say Ashleigh Kelly and her colleagues from the University of Queensland in Australia in a study published in Springer's journal Adaptive Human Behavior and Physiology.

A major goal in has been to understand whether specific features of the body have adapted to serve a purpose, or have merely developed randomly, and to what degree these features are functional. Some evolutionary researchers say that little variety in the size of specific biological features are an indication that these have a very specific purpose or are the result of strong evolutionary selection. Features that are highly variable, therefore, result from weak .

To test this assumption, Kelly and her team investigated human nipples. Male nipples are regarded as a prototypical evolutionary by-product, a non-functional version of the functional female nipple.

Kelly and her team enrolled 63 consenting Australian undergraduate students in their study. Participants' nipple areas were scanned and later measured. The researchers also measured such as participants' height and chest circumference.

Male nipples were on average 36 per cent the size of female nipples. There was also a greater variation in the nipple area size of women, even after taking into account the size difference.

"We found that female nipples were significantly more variable than male nipples," says Kelly, who notes that aspects such as participants' body mass index, the temperature of the room in which the tests were conducted, and differences in the bust size of women, and the chest size of men were all taken into account.

"Female nipples are functional as they are used in breastfeeding," explains Kelly. "Therefore, the finding that females nipples are highly variable discredits previous studies that indicate variation in a specific feature indicates a lack of functionality."

Other researchers have, for instance, claimed that the greater variation in the length of clitorises compared to penises means that the female orgasm is a non-functional by-product of the male orgasm. Based on the current findings, Kelly says that this evidence should be disregarded because the analogy of male and female nipples shows the opposite effect.

Explore further: Here's what you can't post on Facebook (no nude buttocks or cannibalism)

More information: Ashleigh J. Kelly et al, Male and Female Nipples as a Test Case for the Assumption that Functional Features Vary Less than Nonfunctional Byproducts, Adaptive Human Behavior and Physiology (2018). DOI: 10.1007/s40750-018-0096-1

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Ojorf
2.3 / 5 (3) Jun 26, 2018
"Female nipples are functional as they are used in breastfeeding," explains Kelly. "Therefore, the finding that females nipples are highly variable discredits previous studies that indicate variation in a specific feature indicates a lack of functionality."


Only if the feature under investigation has an impact on the functionality. I doubt it does much in this case.
rrwillsj
1 / 5 (2) Jun 26, 2018
D, I think that the evidence shows, at least a possibility. That female nipple size is caused by the function it is intended for.

That all the varying influences in a woman's physiology since her conception? Can cause marked differences among the female population. Rolling the genetic dice among these causations.

Since male breasts are usually not functional. Those do not receive a multitude of biochemical triggers that effect female breasts.

While this specific research seems superfluous, even trivial. Our actual knowledge of what is important causes of women's health issues? And what is not important. Is still being discovered.

The biochemistry that effects nipple-size may turn out to be one of the clues to breast cancer. As much for men as for women.
Da Schneib
3 / 5 (2) Jun 26, 2018
This thread is useless without pictures!

Just kidding.

Seriously, though, I suspect that this is more correlated with breast size than any evolutionary pressure. Now, breast size and evolutionary pressure? That might be correlated. I don't get the impression these folks have examined that.
TheGhostofOtto1923
1 / 5 (1) Jun 26, 2018


The biochemistry that effects nipple-size may turn out to be one of the clues to breast cancer. As much for men as for women.
"The size of your nipple has no relevance to cancer risk, for example," Maggie DiNome, M.D., director of the Margie Peterson Breast Center at John Wayne Cancer Institute at Providence Saint John's Health Center in Santa Monica, CA tells SELF. Likewise, Debra Patt, M.D., a medical oncologist and breast cancer specialist with Texas Oncology, a practice in the U.S. Oncology Network, agrees: "Generally the size variability in the nipple and nipple-areolar complex is not a medical condition, just physiologic variability."

-My god what an idiot you are.
rrwillsj
1 / 5 (1) Jun 26, 2018
Thanks otto for providing the extract from the experts, Dr. DiNome and Dr. Patt. Their opinions on the subject were much more coherent than my own.
Ojorf
3 / 5 (2) Jun 27, 2018
D, I think that the evidence shows, at least a possibility. That female nipple size is caused by the function it is intended for.


Sure, as are the nipples of all mammals, but there can be a lot of natural variation without affecting function.
Look at breast size, no relation to function at all. In fact all our closest living relatives, the great apes, produce plenty of milk with very small breasts (compared to humans).
Human breast size is probably purely a result of sexual selection and has nothing to do with function.
I won't be surprised if nipple size varies for the same reasons.
Da Schneib
5 / 5 (1) Jun 27, 2018
I don't particularly see any natural selection role for cancer. By and large it strikes after procreation has already occurred and thus doesn't have much evolutionary impact. That's why it's so hard to combat; evolution hasn't provided a mechanism to use against it.
Ojorf
2.3 / 5 (3) Jun 27, 2018
I don't particularly see any natural selection role for cancer. By and large it strikes after procreation has already occurred and thus doesn't have much evolutionary impact. That's why it's so hard to combat; evolution hasn't provided a mechanism to use against it.


Yeah, as does a whole host of other problems related to age.
Damn, if only we were the product of an intelligent creator, instead of stupid evolution, life could have been so much better. Ha ha.
rrwillsj
5 / 5 (1) Jun 27, 2018
Djorf, you actually caused me a shudder of horror. The fake godheads that inflict humanity are bad enough. A real deity would be infinitely more capricious and omnipotently more vicious.

My choice is place your bets and roll the dice!

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