If we interbred with them, how are they actually species? It seems more to me you're talking more about racial or breed differences akin to breeds of dogs if two species actually successfuly had viable offspring in the wild.
Did you mean AND (A + C can breed)?
https://en.wikipedia.org/wiki/Zebroid
Darwin's Origin of Species had a good section on this; the book is quite readable.
https://en.wikipedia.org/wiki/Liger
Or are there more significant differences?
Lions/tigers cannot.
They're completely different cats. Panthera leo and Panthera tigris split about 7MYA (est.).
Yeah, I recall Darwin discussing at length how there's no clear difference between a "species" and a "variety". It's a key point, so it's too bad that many people are still under the impression that "species" has an unambiguous definition.
Many of the original work regarding Neaderthals was by 19th-century elite-school scientists with a publication history of eugenics and the confidence that comes from the knowledge of innate superiority of their own kind. Anyone who didn't look like them would be obviously inferior.
They didn't know what we know today -- Neanderthals were light-skinned fair-hared people who had survived for half a million years in the harsh conditions of glacial and inter-glacial Europe and Asia. They had a rich culture of decorative arts and ceremonial burials. They were as capable of vocal speech as we are (same pharyngeal constructs, highly developed Broca's and Wernicke's regions in the brain). They encountered waves of dark-skinned Homo sapiens coming out of Africa and about 10,000 years later vanished from the scene. That there are light-skinned fair-haired Europeans today is evidence that they didn't vanish completely.
The only evidence that H. neanderthalensis and H. sapiens are separate species is the word of 19th-century French aristocrats who were concerned about maintaining racial purity.
This article suggests otherwise: https://www.newscientist.com/article/dn22308-europeans-did-n...
Hell, there's a movement to ditch the current taxonomy structure and pick one of 2 other kinds that seem to follow evolution better than what we have right now.
Wasn't subfamily or tribe originally called race back in the day? I could have sworn when I was in school it was called race. But they changed it at some point without sending me a memo.
Major physical differences (such as wolf) or inability to interbreed or infertile offspring (such as mules) are all just rules of thumb. For instance zebras and horses are clearly distinct species yet they physically appear extremely similar sans their coloring, can interbreed, and there have even been instances of fertile offspring.
Well it does play a role, but in different ways. For instance modern humans are continuing to evolve even though natural selection, in terms of man against environment, is now playing very near 0 role. Instead the factor being selected for now is simple fertility. Humanity will tend to evolve along the characteristics of those families have 3, 4 and more children - while those having 2 or fewer children will gradually fade from the gene pool. So natural selection has in some ways become voluntary, which is quite paradoxical.
However in less developed areas, it's still alive in some ways. For instance if an individual in subsahara Africa somehow developed a genetically heritable mutation making him immune to malaria, it's reasonably likely that all subsaharan Africans would, gradually, become immune to malaria. We can only conclude, putting aside epigenetic factors once again, that such mutations are much less common than e.g. those to the shape of a bird's beak.
Yes, and this has already happened. The African jungle has its pygmies; the Southeast Asian peninsula and surrounding islands have their pygmies; and those two groups are totally unrelated.
This is a tricky concept. Could it be said over 50,000 years ago that Homo Sapiens' ancestors were the mainline? I wouldn't retroactively call it that because it presumes that it was clear at the time that it would be the definitive dominant subspecies.
I think a better phrasing would be "genetic divergences, some of which were preserved by the cross-merging with the only surviving genetic stream", or something of the sort.
And I'm sad so many people just downvoted the comment without clarification. I thought too it was political correctness at first until I looked into the time-frame more closely. It merited a decent reply.