Disease transmission and introgression can explain the long-lasting contact zone of modern humans and Neanderthals

Abstract

Neanderthals and modern humans both occupied the Levant for tens of thousands of years prior to the spread of modern humans into the rest of Eurasia and their replacement of the Neanderthals. That the inter-species boundary remained geographically localized for so long is a puzzle, particularly in light of the rapidity of its subsequent movement. Here, we propose that infectious-disease dynamics can explain the localization and persistence of the inter-species boundary. We further propose, and support with dynamical-systems models, that introgression-based transmission of alleles related to the immune system would have gradually diminished this barrier to pervasive inter-species interaction, leading to the eventual release of the inter-species boundary from its geographic localization. Asymmetries between the species in the characteristics of their associated ‘pathogen packages’ could have generated feedback that allowed modern humans to overcome disease burden earlier than Neanderthals, giving them an advantage in their subsequent spread into Eurasia.

The timing of human adaptation from Neanderthal introgression

“…region is at odds with the hypothesis that the transfer of pathogens from Neanderthals to modern humans necessitated rapid human adaptation using Neanderthal-derived immunity alleles (Enard and Petrov, 2018;Greenbaum et al, 2019). However, it would be interesting to test this idea more generally by attempting to date the start of adaptation for more of these introgressed, putatively immunity-related haplotypes.…”

“…A number of other genes known to influence immunity such as the TLR6-TLR1-TLR10 cluster and HLA class I genes harbor candidates of adaptive introgression, however we did not analyze them as they contain both Neanderthal and Denisovan haplotypes in Eurasian populations (Abi-Rached et al, 2011; Dannemann et al, 2016). The timing of adaptation for the OAS1,OAS3 region is at odds with the hypothesis that the transfer of pathogens from Neanderthals to modern humans necessitated rapid human adaptation using Neanderthal-derived immunity alleles (Enard and Petrov, 2018; Greenbaum et al, 2019). However, it would be interesting to test this idea more generally by attempting to date the start of adaptation for more of these introgressed, putative immunity-related haplotypes.…”

Quantifying the potential causes of Neanderthal extinction: abrupt climate change versus competition and interbreeding

“…The Hominin Dispersal Model, version 2 (HDM2) provides a numerical framework to test existing hypotheses for Neanderthal extinction in terms of sensitivities with respect to bulk parameters of mobility, growth rate, competitiveness and interbreeding. More specific ideas, for instance on social or cultural superiority of HS (Gilpin et al, 2016) over HN, or on differences in anatomy (Hora and Sladek, 2014), hunting techniques or resistance to pathogens (Greenbaum et al, 2019) need to be translated into the bulk parameters of the phenomenological mean field model for hominin density. Another alternative approach to simulate such effects more explicitly is through agent-based modeling (Vandati et al, 2019).…”

Pleistocene Climate Change in Central Europe

“…Violence in early hunter-gatherer societies usually occurred as a result of resource competition following major natural disasters. Another possibility, proposed recently is the spread of pathogens or parasites carried by Homo sapiens into the Neanderthal population [76] Neanderthals possessed the brain that enabled them greater visual acuity than Homo sapiens did, but the latter had better language-processing abilities [77]. It can be stated with certainty that Neanderthal brains were more adapted to vision and spatial memory and that resulted in less available area for cognition and social interactions [77].…”