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I'm Matt Kaplan, the host of Safeguarding Sound Science, Evolution Edition.

Evolution is the unifying principle of biology, yet it still breeds controversy a century

and a half after Charles Darwin.

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We can all spot a children's playground.

Chances are it has colored plastic slides and a walking bridge over an area strewn with wood chips.

Such playgrounds have been designed for children to have fun,

but moreover to keep them safe while doing it. This playground looks very different. This looks like

a junkyard. There are no molded plastic structures, only old tires, some cut in half and filled

with mud, rotten old boards, wheelbarrows,

rickety ladders. The children over there are pounding nails. You're hammering real nails?

Real nails into a board? It's a scene that might terrify parents. So why do researchers studying children's

development recommend dropping your child off here unsupervised? Well, to answer that, we might have to

remember what it was like to have been a child.

I'm Molly Bentley at an adventure playground in New York City.

The effort to remove all risks from children's play suggests we've lost sight of why children

like to play in the first place, or for that matter, why any species likes to play.

It's an important question because play is more than just fun. It has important evolutionary benefits,

and we're not the only ones who like to roughhouse to sled or to chase a ball.

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