This is Scientific Americans 60 Second Science.

I'm Karen Hopkins.

Why did the chicken cross the road?

Well, that's a philosophical pickle.

But if you want to know why chickens don't get cross at people,

why they're content being kept in their coops,

science can help.

Domestic species are interesting

because their genetic makeup has changed dramatically as part of the

process of going from wild to domestic. Lisa Lug, an evolutionary geneticist and anthropologist

at the universities of Oxford and Cambridge.

And indeed when people have compared modern domestic animals with their wild relatives,

they've identified genes that do show signs of strong reason selection.

One such gene is thyroid stimulating hormone

receptor, otherwise known as T. S. H.R. In chickens, a variant of this gene that is

widespread in modern populations has been shown to directly cause chickens to be less

fearful of humans and also result in reduced aggression towards con specifics.

But when exactly did the selection for these traits and therefore this

variant take place? It's been suggested because of the potential usefulness of

these traits in domestic setting that selection on this gene must have happened when chickens were first domesticated around 6,000 years ago in East Asia.

But in an evolutionary time scale, this is just a blink of an eye and we just don't know and

don't have the resolution to tell when exactly between 6,000 years ago and now

...