When There Were Races

"Race" is a term from biology. In that context it means a  biological subgroup within a single species. There are no biological races in Homo sapiens, because the species has a similar heredity everywhere with much in common and only minor ways in which the subgroups differ. 

That wasn't always the case. We used to have human races. 

Scientific work with ancient DNA has determined that about 70,000 years ago, there were five human races on the planet. They were unrelated to what we sometimes call races today.

The old human races were modern humans, Neanderthals, Siberian Denisovans, Australo-Denisovans and the so-called hobbits of Indonesia--and possibly some races not yet detected. 

Only the modern humans survived, but our ancestors mingled with the other four races and had viable young. We have traces of the other races in our genome. 

In California today, we see something similar to that ancient mingling. People of color and people of European ancestry (who are of the same ancient race but differ in skin tones) intermarry and raise children together.  Some things don't change.