Science

I hate how we keep calling them different species....

The various types of hominds are more like the different "breeds" of dogs. Wildly different phenotypes, but they can still interbreed and produce fertile offspring. And they all (relatively) recently shared ancestors.

Horses and donkeys, lions and tigers, these arent necessarily more different phenotypes, but when they produce offspring they're almost always sterile because of a difference in the number of chromosomes which occurs after insane amounts of time where populations are separated.

Eventually the different Homo groups would have become a different species, but not enough time had passed before the next waves out of Africa.

Calling Neanderthals, Denovidians, etc, different species is going to be the same as saying the races were different species 200 years ago.