It Is Empirically Observed That Some 85% of All Human

It is empirically observed that some 85% of all human variation resides within populations. This means that relatively little genetic variation distinguishes different populations. This may be because:

A) there may have been high levels of gene flow among human populations.
B) human populations have only recently spread out from Africa.
C) natural selection prohibits genetic divergence of human populations.
D) sexual selection tends to focus on observable traits.