Since its appearance in Africa, the Homo genus has continually expanded its geographical range. Homo erectus is the first species to have been reliably documented in Eurasia. This first departure from Africa seems to be due above all to the success of a new adaptive model that makes these hominins more independent of the environment. Rather than a migration, it was a dispersal within a vast eco-geographical domain, made possible by the total independence of these forms from the forest environment and a notable increase in their predatory capacities. Nevertheless, man remained a tropical creature for a long time, and these early occupations of Eurasia hardly extended beyond the fortieth parallel of northern latitude. Colonization of mid-latitudes came later, mainly during the Middle Pleistocene, after 800,000 BP. It was thwarted by the increasing amplitude of glacial/interglacial cycles, which had a profound effect on the demography of human populations, particularly in Europe. The geographical and genetic isolation of Pleistocene meta-populations led to the differentiation of Neanderthals, Denisovans and the ancestral forms of modern man. The latter group, after a long and strictly African evolution, and thanks to its unrivalled adaptability, eventually extended its hold over the entire planet, replacing or assimilating all other humanities.
