Nipples often give evolutionary biologists a hard time. Yes, there's the whole “why do males have nipples?” question, but even female nipples pose some big questions.

Nipples come in all shapes, sizes, types, and colors. However, according to a new study published in the journal Adaptive Human Behavior and Physiology, this bold display of diversity could actually question a lot about what we know about human evolution.

One of the big assumptions of evolutionary biology is that low variety in the size of biological features shows they have a very specific purpose or are the result of strong evolutionary selection. Your vital organs are highly complex, specialized, and important body parts, so most humans will be of a proportionally similar size and fairly identical. On the other hand, the theory goes that highly variable features result from a weak evolutionary selection and aren't as functional or necessary. 

However, by measuring the nipples of 63 undergraduate students, researchers from the University of Queensland in Australia have discovered that this is not always true. During the measurements, other factors like bust circumference, body mass, height, and room temperature were also accounted for.

Female nipples are used in breastfeeding, so they have a very clear biological function. In theory, this would be mean that female nipples should have a fairly consistent shape and size, but that’s definitely not the case. They discovered that females have a far greater variation in the nipple size than men, whose nipples were much more uniform.

“We found that female nipples were significantly more variable than male nipples,” lead study author Ashleigh Kelly, PhD, said in a statement.

“Female nipples are functional as they are used in breastfeeding. Therefore, the finding that females’ nipples are high variable discredits previous studies that indicate variation in a specific feature indicates a lack of functionality.”

As a side note, they also found that male nipples were also found to be an average of 36 percent smaller than female nipples.

The research also helps to bust some other myths about human sex organs. The authors note in the study that scientists have previously "claimed that the greater length variation of clitorises than of penises meant that the female orgasm is a non-functional byproduct of male orgasm." In essence, some older studies have argued that the clitoris is merely an "evolutionary glitch", a vestigial penis that has no purpose for women, as shown by the fact they can vary in shape, size, color, etc.

However, this new nippley evidence shows that that idea is hogwash. "This evidence can now be disregarded," the researchers boldly conclude.

Anyway, you’re probably still wondering why the hell males have nipples. Well, that’s a very good question. You can find out more about that age-old question right here.