This is interesting for physical anthropology, because it is about the boundaries that seperate different flora and fauna from each other into the regions that can be identified easily, but between which there is migration, and which change with things like the sea level.

For instance there is no clear biological boundary that can be drawn, between North East Asia and South Asia east of the Himalayas (which are a boundary). Therefore we should expect population migrations between the north and the south there, which we can trace, by genetics and physical similarities. The relative seperation of Subsaharan African populations, is also related to a geographical boundary, the Sahara. In East Africa the seperation has been less clear.