The human genome is incredibly homogeneous when the widespread distribution throughout the world is considered. This is due to a fairly severe genetic bottleneck at the last ice age as well as the fact that we are constantly moving about and fucking everything that moves.

I had a professor once who said that if aliens came to earth and examined humans they would think we all originated from a population of clones because we are all so alike, I don't know how true that is, but I like the anecdote.