Hey short waivers, Regina Barber here.

Today, we're going back to school.

It's been a while since we've done one of these episodes

where we revisit a science topic you may have learned about

and go a little deeper with it.

You might remember a list of life, a set of bullet points

that are THE criteria for being alive.

They include things like being highly organized, like the machinery inside a cell,

using energy and responding to the environment.

So, something that could reproduce itself,

they have to be able to have a metabolism, also growth.

That's developmental biologist Crystal Rogers at University of California Davis,

and she thinks about life a lot.

So my lab studies how embryos develop from a single cell into a complex organism.

And she says, even though we have this list,

defining life is not that straightforward.

Can we boil it down to like something... one thing?

I don't think so, because I think all of us have our different perspectives on life.

And even though it's a tricky question, Crystal thinks life is worth defining.

There are things we would do to non-living things, like use them for resources,

build a house out of a tree, which is alive, and then we've now killed it,

and now it's just a thing, right?

...