The print publication - in the November 3rd Science magazine - goes into even greater detail on the evidence for widely distributed and socially structured outbreeding in even very early populations of hunter-gatherers of our lineage. Apparently even the earliest groups were not at all inbred, and must have formed breeding populations much larger than the groups themselves involving routine mate exchange over fairly long distances. This is thought (by the authors) to be reflected in the genetic exchanges with Denisovans and Neandertals as well as other sapiens or their forerunners.
