Following Pleistocene road signs of human dispersals across Eurasia

The present paper is an endeavor to summarize the evidence for various dispersals of hominins into Eurasia, while avoiding the commonly held assumptions that these events, whether short or continuous, were triggered by climatic conditions or were part of dispersals of other mammals. Non-continuous archaeological records from well-explored regions are used as the basis for the hypothesis that lineage extinctions resulted from physical, technical and social failures to adapt to new and demanding environments, as well as from the aggressive behavior of "free riders" The late development of altruism and social cohesion, at the level of group and kin-selection, delayed occupation of regions suitable for the survival of Early and Middle Pleistocene hominins. Only intra- and inter-group behavioral changes of forager bands, accompanied by technological innovations and/or inventions, as well as efficient forms of systematic teaching of survival skills, facilitated the colonization of larger areas, whether empty or already inhabited. Besides Eurasia and Sahul, all of the above enabled the crossing of the ecological "northern boundary", leading to later migrations into the Americas. Each of the dispersals had its own, particular history, and even if many details are still missing from the archaeological record, the emerging picture is much more complex than was assumed a decade ago.