627-594 thousand years ago
We’re getting to a time on the blog when Homo erectus (and Homo ergaster, if we accept that erectus-like African specimens are another species) are starting to give way to the very earliest ancestors of later species – Homo sapiens, Neanderthals, and Denisovans. (Denisovans – known mainly from DNA rather than bones – are the contemporaries in East and Southeast Asia of Neanderthals in West Eurasia, and early sapiens in Africa.) A recent article from Alan Rogers (a colleague of mine in Anthropology at the University of Utah) and Ryan Bohlender and Chad Huff (Utah Anthropology PhDs) sheds light on this period. The authors look at the distribution of shared derived mutations in two modern human genomes (African and Eurasian) and two ancient genomes (Neanderthal and Denisovan). They fit a model involving past divergence times and population sizes to the data. The model says that about 700,000 years ago. a small population split from the rest of humanity and then quickly split again to give rise to the ancestors of Neanderthals and Denisovans. In other words, it looks like there was an Out Of Africa event in the Middle Pleistocene, well before the better known Out Of Africa event that gave rise to modern human populations around the world. The ancestors of Neanderthals and Denisovans then replaced Homo erectus in Eurasia, although the authors find signs that some erectus genes may have made it into the Denisovan gene pool. This also implies that Homo antecessor in Europe was a dead-end branch of Homo erectus, not a Neanderthal ancestor.
As paleoanthropologist John Hawks notes, in a commentary on the article, “Humans stand out among our close primate relatives as effective biological invaders. Our recent history has included range expansions into remote and harsh geographic regions, and invasions by some populations into areas long occupied by others.” We’ll be seeing more instances of this in days to come on the blog.
And here’s me on what a later history of population replacement might mean for the evolution of ethnicity and ethnocentrism.