Clip | The Egg: Life’s Perfect Invention - How an Egg Hatches

How is it possible that an egg can be strong enough to provide protection, yet soft enough that a baby bird can break through? See the remarkable way hatchlings are able to break out of their eggs.

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[Narrator] But how do the chicks break out from the cramped confines of the egg?

How can the shell that's been strong enough to protect the chick from the outside world, be also weak enough to allow the chick to break it?

The first breath of fresh air outside the egg.

A captive-bred jungle fowl chick emerges.

It's the climax of the egg's existence.

The shell may look the same as when the egg was laid, but out of sight, it's been changing.

It's been getting thinner.

The chick has been absorbing calcium from the shell into its own bones, making itself stronger and the shell weaker.

Not only that, but it also used the shell's calcium to create a tool to help it break free: A hard, jagged tip on the end of its beak - an egg-tooth The chick couldn't have broken free without it.

Even so, it can still take hours, sometimes days, to hammer its way out of a shell.

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