Why Are Baby Animals Born So Different?

Step 1 of 5

Finishing a baby costs the mother.

Everything a baby is born with had to be built inside the mother first. A more finished baby means a longer pregnancy and a much larger animal to carry around.

Step 2 of 5

Prey on open ground has no choice.

A foal born helpless on a plain would simply be eaten. Everything about a horse's pregnancy is spent making a baby that can stand and run before the day is out.

Step 3 of 5

A safe nest buys time.

An animal with a burrow, a den or a nest can leave its young somewhere hidden. Then a baby can afford to be born unfinished and do the rest of its growing outside.

Step 4 of 5

Growing outside is the cheaper way.

A baby that finishes its growing outside gets fed by a mother who is still eating and moving freely. The other way, it has to be built out of her body while she is heavy and slow.

Step 5 of 5

Brains almost always finish last.

Even in animals born ready to run, the brain keeps building for a long time afterwards. Learning is cheaper than being born knowing, as long as something is looking after you.

A human baby is unusually unfinished. A newborn cannot hold up its own head, which is the price of a head that large.