Why do men have nipples?

Have you ever noticed that the younger kids are, the more alike boys’ and girls’ bodies appear? After all, they have a lot in common: two arms, two legs, one head, two nipples.

But as kids become grown-ups, their bodies start developing differently. One of the more obvious differences is that women grow breasts in the chest area, underneath the nipples, and men do not.  The breasts are important because if a woman has a baby, she can feed the baby by helping it nurse milk out of her nipples. It’s part of how humans have evolved to care for their young.

So why do men have nipples if they don’t have breasts and they don’t nurse?

Because there’s really no reason to get rid of them!

You see, men and women share a lot of the same genetic map for making their bodies. As babies in the womb, we all have basically the same sets of tissues and organs at the very beginning. At some point in our evolution—the long process by which a species gains helpful characteristics like thumbs and loses inconvenient features like tails—females developed nipples as a way to help nurse their young. Nipples on a male aren’t very useful, but they don’t do any harm either. There simply was no reason for men to lose nipples at any point in human evolution.

Did you know that lots of animals have nipples? All mammals nurse their young—it’s part of what defines a mammal! Can you think of other kinds of mammals besides humans? 

Play the mammal charades game! With a friend or a parent, pretend you’re a mammal. Act like a horse, a cat or some other mammal. Can your friends and family guess the animal?