There's enough of a genetic difference between subpopulations that if you spit in a cup and ship it to 23andMe, they can tell you where your ancestors came from. Also, there's enough of a difference so that if your ancestors aren't from West Africa, you'll never win an Olympic medal in sprinting[1].

FWIW, people that study population genetics sound shockingly racist. Science is science, whether or not we want it to be.

[1] http://m.theatlantic.com/entertainment/archive/2013/08/the-u...