What does the word extinct mean?

It means the species doesn't exist anymore, right?

It means every member of the species that ever existed has now died.

How do we know when an animal is extinct?

Now, that's a harder question, and I think the answer is we don't.

This is a philosophical problem more than a practical one. Typically, you just can't prove something

doesn't exist anywhere. You can only note that you haven't observed it in the places you've looked.

Nobody has seen a purple duck, for example, as far as I'm aware.

We've seen lots of ducks. None of them were purple. And so we're pretty sure that ducks just

don't come in purple, but it would be impossible or nearly impossible to

prove that they don't exist. Even if we are sure enough to say in conversation that we quote

unquote, know that there are no purple ducks out there. We don't know. If we found just one purple duck, just one, we would be immediately

proved wrong. And that is one of the funny things about evidence. Proving a positive claim to

existence takes just one data point, one example, and you've done it. But virtually all the data points in the

world can't prove a negative. The same applies here. We can have really, really good reasons to

think an animal is extinct. We can have reasons so good that we can and should say that we know they're extinct.

It would be ridiculous to feign ignorance about their extinction, and it would make the word extinct,

a very useful word, impossible to use.

So how do we know an animal's extinct? Here is a group of three reasons, that if I were

given all three of them, I would say, yeah, we know they're extinct. First, say we looked into the

strata of the earth, we saw a fossilized species, and we noticed that fossils for that species just stopped appearing after a certain layer.

They're there at the deeper, older layers, but they don't exist in more recent layers.

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