From my understanding it has a lot to do with environmental factors, like people in different geographic reasons with different weather have developed varying physical traits to survive those environments. As for where humans came from...well for all I know we aren't even natives to this planet, but who knows. But maybe there is a better term than race for these environmental/geographic evolutionary differences than race.
I know in the context of like fantasy novels/movies...humans are a race, elves are a race, dwarves are a race, orcs are a race ect., so in that context it would seem the term race would not be used to distinguish two humans from different regions who have physical appearances reflecting that.
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Metal never dies. \m/