Past human expansions shaped the spatial pattern of Neanderthal ancestry

Area of Science:

• Paleogenetics
• Human Evolution
• Population Genetics

Background:

• Modern humans (Homo sapiens) and Neanderthals coexisted and interbred before Neanderthal extinction.
• Observed differences in Neanderthal introgression levels between East Asians and Europeans have been attributed to selection.
• An alternative hypothesis suggests range expansions of Homo sapiens created spatial introgression gradients.

Purpose of the Study:

• To investigate the presence and persistence of Neanderthal introgression gradients following past human expansions.
• To analyze spatiotemporal variations in archaic introgression to infer human population dynamics.

Main Methods:

• Analysis of Eurasian paleogenomes.
• Investigating spatial patterns of Neanderthal ancestry across different human expansion events.

Main Results:

• The Out-of-Africa expansion of Homo sapiens created persistent spatial gradients of Neanderthal ancestry.
• Neanderthal introgression gradients were maintained through time.
• The expansion of Neolithic farmers reduced Neanderthal introgression in Europeans compared to Asians, as farmers carried less Neanderthal DNA than hunter-gatherers.

Conclusions:

• Spatial variation in archaic introgression provides insights into past human population dynamics.
• Range expansions, rather than solely selection, shaped Neanderthal ancestry patterns in humans.
• The Neolithic expansion played a significant role in differential Neanderthal introgression across Eurasia.