Wednesday, 24 January 2018

Did humans reach Asia earlier than we think?

Map of early human migration
NordNordWest (public domain)
An insightful perspective in Nature Ecology and Evolution (abstract here) questions if there was just one successful dispersal of Homo sapiens from Africa to Asia. The current consensus - the Out of Africa Hypothesis (here) - is that modern humans left Africa some 65-55 thousand years ago and rapidly spread around the globe (see map). 
Stone hand axe from Wadi Dabsa, Saudi Arabia
From Foulds et al. (here)
An earlier migration from Africa to the Levant is supported by fossils and increasingly by archeological evidence, including from recent digs in the Arabian peninsular (here). Hitherto this exodus has been regarded as short lived and restricted in geographical extent.

Leveraging the increasing amount of evidence emerging from Asia, Rabett argues that, on the contrary, this first dispersal reached far beyond the Levant with populations surviving for many thousands of years.

Therefore he questions whether all the sites attributed to Homo sapiens in Southeast Asia and Australia stem from a single dispersal. Some sites from 45-65 thousand years ago might represent late-surviving enclaves of an earlier dispersal. At the very least, much of the archeologcal data conflicts with a rapid dispersal along the Southern coastal route.

Genomic data including ancient DNA support the view that all human populations living outside Africa derive from a single exodus albeit there was subsequent admixture with other hominins (including Neanderthals and Denisovans). The earlier migration did not contribute to the extant human gene pool. But to quote Rabett, "should evolutionary success be measured only by genetic and demographic continuity into the present?"

No comments:

Post a Comment