How do we decide what counts as a new species and what’s just a variation within a species?

Question

I grew up hearing that the main indicator of a species was that they only reproduced with one another. But Neanderthals and Humans cross bred. And they’re separate species. And in captivity Lions and Tigers can breed, but they’re obviously different species. Like I guess I’m just confused where the line gets drawn when deciding what is and isn’t a different species.

In: 50

Answer 1

Of the two examples you mentioned, yes, they can interbreed, but the offspring are generally infertile, though not always.