Hey short waivers, Regina Barbara 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 some 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? Whether a rock is alive, I don't think so, but the bacteria that's living on it is probably alive. So I don't know if I have an answer to your question, except for the idea,

it's important to understand what life is so that we don't destroy it and so we can protect it.

Today on the show, what is life? The standard criteria, but also why defining it is so hard.

Plus, we get a little sci-fi by imagining what life might look like outside of Earth and ask,

is the Star Trek character Data, who is an android, alive?

I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR.

Okay, Crystal, so the classic items on the so-called list of life are having an organized structure, reproduction, growth, and development, using energy, trying to maintain

homeostasis, responding to environment and adaptation. Okay, let's dig into a few of these.

So for me, as a developmental biologist, growth is a big part of what we study. The concept is

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