This is an I-Heart podcast.

There's a vile sickness in Abbas town.

You must excise it.

Dig into the deep earth and cut it out.

From IHeart podcasts and Grimm and Mild from Aaron Manky,

this is Havoc Town. A new fiction podcast set in the Bridgewater Audio Universe, starring Jules State and Ray Wise.

Listen to Havoc Town on the IHart Radio app, Apple Podcasts, or wherever you get your podcasts.

Welcome to Brainstuff, a production of IHeartRadio.

Hey, Brainstuff, Lauren Vogelbaum here.

I want to talk to you about one way that mice could be considered more highly evolved than

humans, nipples.

Whereas human males develop a pair of nipples, or sometimes more, that generally serve no biological function, male mice exit the womb with their bellies smooth and nipple-free.

So why do men have nipples?

Come along with me as I explore embryonic development.

Three or four weeks after conception, all human embryos develop parallel mammary ridges called milk lines.

They extend from the top of the chest to the lower abdomen.

At that stage, the embryo still has what scientists refer to as indifferent gonads,

meaning they're still capable of developing either into testes or ovaries.

It's not until week seven or so that genes in the embryos sex chromosomes kick in.

You know, usually XX or XY, but there's a bunch of variations.

They're what caused the formation of sexual dimorphisms,

the physical traits that distinguish the typical biological male from the typical biological

...