Neanderthals and humans were a separate species, however they interbreed over the course of thousands of years and eventually the Neanderthals disappeared. This would indicate that we were the same species, however the Neanderthal genome has been studied and we know they were a different species. We could also find that they genetically had the same vocal cords as humans and a finding in the throats of our common ancestor indicated that Neanderthals probably had the same vocal cord setup.
So what if Neanderthals never went extinct?