How did early humans and neanderthals manage to produce fertile

Same number of chromosomes.

>>8584678
>>8584687
This.

Anyway, you can't dispute it, since Europeans and Asians HAVE Neanderthal DNA.

>>8584695

I get that, but a species is often defined the major subdivision of a genus or subgenus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of another species.

>are not able to breed with members of another species.

>>8584700
What about hybridisation, such as the coywolf?
They are comprised of two 'separate' species.
>https://en.wikipedia.org/wiki/Coywolf
You're welcome, /thread.

>>8584700
It's futile to seek or defend a rigid definition of species. Stuff like ring species wreck the concept. Gene pools are huge and diffuse things, not neat classes.