Based on the fossil record, humanity began its journey out of Africa perhaps 100,000 years ago. Since then, as people settled in various climates and environmental conditions, the flavors of mankind-- the races-- evolved.
As humans settle space and colonize other worlds, evolution can be expected to continue to work its will. Space humans may develop a resistance to radiation, for example. Populations that live for generations in low gravity situations may grow taller, thinner, and less muscular. At some point in the distant future, descendants of generations away from Earth may find it physically uncomfortable to live on Earth.
Of course, this time, humans will have the ability to intervene in the biological evolution of the species by manipulating genes, taking evolution in a particular direction, speeding it up, or slowing it down. That kind of control over the essence of ourselves clearly has huge moral implications, but going into space will challenge humans in ways we cannot yet imagine.