The Bible tells us that humans are all one race, one blood, and scientists--even secular ones--confirm that. We may have different facial features, different skin tones, and different genetic tendencies, but we are all one race. (Next time you get a political phone survey that asks your race, try telling them 'human' and see what they say.)
But in writing speculative fiction, we have a little bit of freedom to play with that. God created our world with only one race of sentient creatures created in His image, but who is to say He might not do things differently in another world?
J.R.R. Tolkien's writing is the obvious choice as an example. Middle Earth is populated by several different races: humans, hobbits, elves, dwarves, goblins, and usually there are a variety of sub-categories within each race as well. In that case, each race is basically a distinct creature all its own.
In the fantasy world where my current WIP is set, the term 'human' refers to any creature with a living soul; physical characteristics have nothing to do with it, so even sentient dragons are considered human. Needless to say, there are distinct races among the humans in that world, some more drastically unique than others, but each with its own characteristics and traits.
And there could be many other ways to address the issue of race in fiction, too. Maybe there is a fictional world where no creature is 'human' as we know it. Perhaps in one world, elves and dwarves are just variations within the human 'species'. We serve a creative God, so I'm sure there are millions of ideas out there that we haven't even thought of yet.
What is your approach to race in your writing?