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

I’ve witnessed heated arguments on social media between biology professors arguing over whether to define something as a species or a subspecies. Even the experts don’t have an agreed definition for much of the taxonomy.