The earliest hominid dispersals beyond Subsaharan Africa: A survey of underlying causes

Abstract

Although anthropogenesis reaches back to Pliocene times in Subsaharan Africa, hominid dispersals beyond began only by the Early Pleistocene, with the appearance of genus Homo with Lower Palaeolithic repertoires. Causes responsible for these events remain poorly understood. Direct evidence for environmental factors, such as prolonged aridity stress or linkage with emigrating African ungulate or carnivorous species, while plausible, remains weak or ambiguous. Bio-cultural evolutionary evidence, however, provides more compelling indications, supported by empirical findings. These are rooted in the hominid ‘dual heritage’ involving higher primate ancestry and a partly but significant zoophagous dietary shift. Several million years of evolutionary divergence separated early Homo from its pongid relatives. The consequences of an omnivorous–carnivorous shift, on the other hand, besides enabling harvesting food resources at different levels of the trophic pyramid, included ‘natural history intelligence’, observed commonly among social carnivores. It enhanced human–landscape–plant–animal relationship and knowledge. It also favoured home-ranges expansion and the eurytopic adaptability of mobile ancient foraging hominids, as well as ecological polymorphism. The latter enabled hominids to adapt and exploit an increasing range of ecosytems, from the semi-arid tropics to subtropical steppes or woodlands, Mediterranean habitats, temperate woodland/grasslands, and a diversity of tropical forest formations in Eastern Asia. This adaptive versatility, linked with encephalization, particularly the expansion and increasing complexity of the brain cortex surface, was reinforced by cultural behaviour, best documented by technological behaviour. Lower Palaeolithic toolmaking demonstrates another behavioural discontinuity or technological ‘mutation’ by a familiarity and mastery, as ‘first geologists’, in acquiring suitable minerals, and skill in producing and using tools, as ‘secondary energy traps’ for various purposes, including prey carcass processing. Intermittent fire production represents another ‘mutation’ implying that hominids were virtually unique in overcoming the genetically inherited pyrophobic response, common among mammals. Cultural behaviour, as domain of socially acquired and transmitted interpretation and meaning of events, objects or activities, for mediating the world, pervades various aspects of human life (technology, subsistence, social life, cognition). It inserted progressively a new ‘cultural environment’ to which hominids became increasingly adapted and reliant on. This African dual heritage and bio-cultural evolutionary path documents how early hominids began following a new, hitherto unexploited adaptive niche, illustrated by long-range dispersals and gradual colonization of Eurasian ecosystems throughout the Pleistocene. This expansion became increasingly non-biological and contingent on cultural repertoires.