[lurquer]

It isn’t a continuum, though. There are distinct discontinuities. Chromosome count is one such example. Polar bears and grizzlies have 74 chromosomes. A panda has 42.

You can’t gradually go from one to the other.

Absent some mechanism we don’t know about, conception simply doesn’t work when the sperm and eggs have different numbers of chromosomes.

To be clear, the concept of chromosome isn’t as objective as one might think… nevertheless, it’s an example of the type of genetic difference that simply precludes reproduction.

[AlotOfReading]

Horses and Donkeys have differing numbers of chromosomes and yet (extremely rarely) produce fertile mules. In a more common case, women with down's syndrome have an extra chromosome and yet are sometimes fertile. I understand that this is extremely common with plants, but that's pretty far outside my wheelhouse.

I don't think we're disagreeing here, just simplifying like all conversations about biology.