I had race on the mind, as am in the midst of reading Nicholas Wade's `Troublesome Inheritance: Genes, Race, and Human History'. As he explains well, races exist, are not skin color, and the boundaries are not sharp, but are represented by clustering of genetic characteristics. I say: ditto for your 'branches'. Of course, what's actually clustering today is going to be different from 75,000 years ago.
For some reason, the existence of a biological basis for race, which seems obvious to most, triggers a lot of people, including many geneticists. Go figure.
Because the concept is backwards and derails the progress of science (in biomedicine it leads to a lot of confusion and wasted resources). And it's actually because the boundaries are so smeared and undefined. A hippo may look closely related to an elephant or a horse (as science used to believe), but its closest relative is a whale! Similarly people's skin colours, etc.
I'm disputing the concept of race on the grounds on statistics and the genetic and anthropological research I've read - you could respond likewise instead of suggesting that I'm of getting "triggered".