It was originally meant to be a "nicer sounding" synonym for "subspecies", which is what the various human races are. Same species, different subspecies. Like different types of wolves or squirrels. Very similar and capable of interbreeding yet visually and behaviorally distinct in their own ways. The differences were brought about via divergent evolution/speciation. That is to say, the various human groups were in the process of becoming separate species but didn't evolve divergently for quite long enough for the process of speciation to fully complete thus they are intermediate species or "subspecies".
[–] EnigmaSigma ago
It was originally meant to be a "nicer sounding" synonym for "subspecies", which is what the various human races are. Same species, different subspecies. Like different types of wolves or squirrels. Very similar and capable of interbreeding yet visually and behaviorally distinct in their own ways. The differences were brought about via divergent evolution/speciation. That is to say, the various human groups were in the process of becoming separate species but didn't evolve divergently for quite long enough for the process of speciation to fully complete thus they are intermediate species or "subspecies".