Fragmentation of Neanderthals' pre-extinction distribution by climate change

Neanderthals lived in Eurasia alongside anatomically modern humans (AMHs) until some 40,000 years ago. The extinction of Neanderthals is attributed to either climatic change, or to the effect of competition with AMHs. We used fossil occurrence records and paleoclimatic data to model the potential distributions of H. sapiens and H. neanderthalensis using Species Distribution Models, and calculated the degree of habitat quality and connectivity at successive time steps. We found that both species potential geographic ranges progressively retreated from their northeastern borders beginning with 44 ka. Although the degree of habitat loss is similar for the two species, the potential range for H. sapiens was constantly some 50% larger on average. The degree of habitat fragmentation, and the size, number, and average distance between optimal habitat patches was initially very similar for the two species. However, all these landscape metrics showed a progressive deterioration for H. neanderthalensis only over time. At the end of their existence, the most suitable habitat patches for Neanderthals were small and isolated, and their inferred climatic niche width was statistically narrower than in H. sapiens. This does not mean that climate worsening drove Neanderthals extinct, yet it suggests extinction risk for the latter markedly increased over time, towards its actual extinction date.