Milankovic cycles and Cultural Evolution as Important Catalysts for Hominin Genetic Diversification

Abstract

Climate variability is widely considered a key driver of human evolution, yet the mechanisms linking long-term climate change driven by Milankovi[c] cycles to hominin demography and genetic diversity remain elusive. Here we couple an agent-based demographic model, incorporating an idealized genetic marker, cultural dynamics, and a realistic Pleistocene climate framework, to quantify how astronomically forced climate and vegetation variability shaped the genetic structure of African hominins over the past 1.9 Myr. We show that warm early Pleistocene climates sustained a continent-wide network of genetically diverse demes until ~900 ka. The subsequent decline in atmospheric CO2, associated cooling, and reduced vegetation during the Mid-Pleistocene Transition triggered widespread demographic collapse, with populations surviving only in southern and eastern Africa. This reorganization in population structure leads to a decline in simulated genetic diversity, consistent in timing with genomic and archeological evidence. Introducing cultural innovations in the model, represented as enhanced carrying capacity, enables hominin populations to recover from this diversity bottleneck, adapt to increasingly harsh late Pleistocene environments and long glacial periods, rapidly expand across Africa during interglacials, and ultimately disperse into Eurasia. Our results identify Milankovi[c]-scale climate forcing and cultural growth as important catalysts of hominin population structure and genetic diversification.