The definition of a species is not limited to being able to produce offspring or even fertile offspring. Lions and tigers can have offspring (ligers) who are sometimes fertile yet I doubt anyone would consider them the same species.
More fundamentally even if we decide that all homo lineages are the one species, it is the ignoring of all these lineages and the interbreeding between them that is the interesting observation. We now know that Neanderthals did not become extinct yet this is total ignored.
More fundamentally even if we decide that all homo lineages are the one species, it is the ignoring of all these lineages and the interbreeding between them that is the interesting observation. We now know that Neanderthals did not become extinct yet this is total ignored.