wolves and coyotes have these big upright ears.

All the better to hear you with.

But my dog Zeke here has floppy ears.

Why the difference?

Doesn't he need to hear too?

Charles Darwin himself actually thought a lot about this question.

150 years ago, he published a book that said, "Look—it's not just pet dogs!”

Pigs have floppier ears than wild boars.

Farmed goats have floppier ears than wild goats.

There are floppy-eared rabbits, cows and sheep.

And that's not the only weird thing!

Tame animals tend to have shorter snouts, and their fur tends to be paler

or have patches with color missing.

All these mysterious traits put together have been called "domestication syndrome."

So, what's going on here?

The story starts thousands and thousands of years ago

when humans were surrounded by animals.

Some animals were scary,

and some were a bit more approachable

even potentially useful.

Our ancestors wanted them to be tamer, so sometimes

they tried breeding the friendliest ones.

At some point, strange side effects started to show up

Thousands of years later, good old Darwin noticed the domestication syndrome pattern,

but all he'd learned about change in the animal kingdom

couldn't explain this connection between behavior and appearance.

Scientists who came after him couldn't figure it out either.

But for the past few years, scientists have been throwing around a fascinating hypothesis.

They think the answer to this whole puzzle lies in a special group of cells.

They're called neural crest cells, and coincidentally,

they were discovered by Wilhelm His the exact same year Darwin published his book.

Neural crest cells show up very early in the development of all vertebrate embryos.

As the embryo grows into a goat or a pig or a wolf,

these special cells travel to every corner of the body

and take on all sorts of different jobs.

Now, here's the thing: Some of these cells end up right here above the kidneys.

They become cells that secrete adrenaline

—that famous fight-or-flight hormone.

Wild animals are always fighting or fleeing to survive,

and that makes it hard for humans to get close.

But what if an animal was born with fewer of these neural crest cells,

or those cells didn't work so well?

That animal would have less adrenaline.

It would probably be less freaked out by humans—

and it would pass that behavior on to its offspring.

The idea is that this is what's going on in domesticated animals.

Their neural crest cells have been dialed back.

And this would explain all the appearance stuff, too

because neural crest derived cells do a lot more than just make adrenaline.

Some of the cells end up forming parts of the face.

Some of them become cells that control the color of skin and hair.

And some make their way into the ears—and help make cartilage.

It's likely this is how dogs first got floppy ears.

And then centuries of intentional human breeding helped accentuate or reverse that change.

But the neural crest cell hypothesis doesn't quite explain every bit of domestication syndrome.

Like—what's going on with other tame species that do have upright ears?

This be might be the excuse scientists need to spend more time with their pets.

This is Skunk Bear—NPR's science show

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