lanstin parent
What there isn't is a small number of distinct subgroups that are more related to each other than to the other subgroups.
Sure there are. An easy example is Australian aboriginals. They were geographically isolated for tens of thousands of years. Their subgroups are more related to each other than to other subgroups.
There is, due to the way humans migrated and geographically isolated themselves over human history where founder effect, genetic drift, and evidence for introgression (both within our species and from hybridization with other species of hominids) is easily appreciated among populations even today.
http://www.stat.yale.edu/~jtc5/papers/CommonAncestors/Nature...
Strong statistical signals but no sharp lines between groups - we as a species like travel and sex.
Depends on the group. Oldie but goodie (1). Salient quote: "The Mormon gene frequencies are similar to those of their northern European ancestors. This is explained by the large founding size of the Mormon population and high rates of gene flow. In contrast, the religious isolates (Amish, Hutterites, and Mennonites) show marked divergence from their ancestral populations and each other, due to isolation and random genetic drift. "