Australian Science Illustrated — Issue 54 2017

26 | SCIENCE ILLUSTRATED

ASK US

Think of the

craziest rooster

you ever fl ed from

and multiply by

about ten

ANATOMY OF AN EGG

NINE LABELS! // And still a simplified diagram of a typical egg. The

germinal disc contains the DNA and stem cells that grow the actual chick.

THICK ALBUMEN THIN ALBUMEN

CHALAZA

YOLK

VITELLINE MEMBRANE

AIR CELL

CUTICULA

EGGSHELL

GERMINAL DISC

It’s a bit like growing up. You never

really think of yourself as being bigger than

you were 20 years ago. But the

photographic evidence is clear. You used to

be really small. But the growth happened so

slowly, it only struck you every now and

then how big you were getting.

Now, this isn’t the same mechanism as

evolution, but it gives a sense of how

gradual the process is.

From ancestor bird to chicken, a long

unbroken line of birds kept laying eggs,

each chick was slightly different to its

parents, and over millions of years these

differences built up to a point where the

bird now looked like what we call a chicken.

This is true of how animals involve, but in

the specific case of the CHICKEN and the

CHICKEN EGG, we didn’t need to get into

evolution. Because it

turns out the answer to

this question is really

easy, and doesn’t require

any knowledge of

evolutionary theory at all.

One day there was a

bird that wasn’t a

chicken, and it laid an

egg, and that egg

hatched into a chicken. How do we know?

Because we were there and, very probably,

we made it happen.

Specifically, humans in Asia no earlier

Like dogs, chickens have

the genetic ability to be

bred into hundreds of

different phenotypes.