Climate And Archaic Hominins

John Hawks has an intriguing analysis of a new paper on how the range and interactions of Neanderthals and Denisovans may have had a climate component. We know from the existence of genetic evidence showing Neanderthal-Denisovan admixture that there was some interaction.

He is skeptical of some aspects of the paper, including the hypothesis that Denisovans were systemically more cold tolerant, and the underlying concept of that there was a stable over time geographic range of occupation by particular species with frontiers that were rarely crossed. He acknowledges, however, that there is a wide geographic range where they could have been Neanderthal-Denisovan interaction. He also notes that:

The conclusion I draw from Ruan and colleagues' study is that no strong east-west climate barriers could have kept these populations apart for the hundreds of thousands of years of their evolution. That leaves open the possibility that other aspects of the environment besides temperature, rainfall, and general biome composition could have shaped their evolution. The alternative is that the survival and local success of hominin groups was itself so patchy over the long term that only a handful of lineages could persist.

One hypothesis that I've advanced over the years is that the jungles and hominin occupants of mainland Southeast Asia, formed a barrier to Neanderthal and modern human expansion until the Toba eruption at least temporarily removed that barrier.

I reproduce two images he borrows from papers he discusses below: 

One issue with the Denisovan habitat range shown is that Denisovan admixture in modern humans is strongest to the east of the Wallace line and together with residual Denisovan admixture in Southeast Asia and East Asia (albeit greatly diluted) suggests a much greater warm temperature range for these ancient hominins than the chart above suggests in both island and mainland Southeast Asia.