All these groups resemble their immediate neighbors more than they do groups farther away because of the continual exchange of mates across group boundaries. There's a simple way of describing our genetic relatedness. Not only do all people have the same set of genes, but all groups of people also share the major variants of those genes. Geneticists have never found a genetic marker that is of one type in all the members of one large group and of a different type in all the members of another large group. That's why ethnically targeted biological weapons would never work.
Every group overlaps genetically with every other.
The extreme interpretation of this observation, now popular in academia, is that biological groups do not exist. That's obviously absurd. But the development of morphological differences in a widely distributed species is a biological commonplace. Whenever the members of a group are more likely to mate inside the group than outside, the frequency of particular genetic markers within that group can become higher or lower. But natural selection can also be a factor.