How did human races form?

Nina - Well, it's a big question and one can argue that there are no such things as human races, because human races are basically defined by us socially. When you go to Britain or the United States or Brazil or India there would be different groups that would be defined as different races. In many respects races don't exist. What we do see are lots of patterns or genetic variation. Some of these patterns are related to our appearance but those are just a tiny fraction of our genes that actually contribute to these differences in appearance. We have tremendous amounts of variation that don't coincide with these classic racial groups that have been defined in various places. The long and short of it is races are an outdated, ancient construct that we'd best ignore.