Dispersals, evolutionary change, and innovation
Hominins differ from other mammals in the extent of their anatomical changes, and also in their capacity for cultural change. The most obvious evolutionary change in the hominin lineage is the increase in brain size over the last 2 million years, from c.
600-750 cc. at Dmanisi to 1,200-1,500 cc. in Neanderthals and Homo sapiens. This increase in brain size was accompanied by a shortening of the gut, and was probably caused by the way hominins shifted towards carnivory and the regular intake of high-quality protein: this reduced the need for a long digestive tract suitable for processing low-quality plant foods, and under-pinned the expansion of energetically expensive brain tissue.[554] As noted above, stone tools would have given hominins an edge over their competitors in enabling them to deflesh carcasses and extract marrow; these skills in turn also depend upon a large brain. In this instance, carnivory and tool-making may have been the impetus behind the earliest dispersals of our genus from Africa.As hominin brains became larger, so the amount of information that they could store and process increased. Brain size in primates is correlated with group size, as large social groups involve greater skills of communication (including language) and negotiation. As group size increased, the social landscapes of hominins would have become larger and more complex, and included factors such as mapping the location of scarce resources (such as high-quality stone), and the developing exchange networks. In short, the development of a ‘social brain' would have widened the potential scope for hominins to disperse into new types of environments, or to utilise them more effectively.[555]
The ability to disperse into new types of environments in Asia is most pronounced for Homo sapiens in the last 50,000 years. For over a million years, the hominin range did not increase significantly.
However, in the last 50,000-60,000 years, several new type of environments were colonised for the first time. The most striking in continental Asia is the colonisation of Siberia, which probably began c. 40,000-50,000 years ago, and which brought humans to the Arctic Ocean and ultimately to North America via the Bering landbridge c. 15,000 years ago.[556] As major an event was the colonisation of the Australian landmass in the last 50,000-60,000 years, which would have required the use of boats or rafts with paddles and sails, as well as some navigational abilities. The development of navigational skills also led to the colonisation of Japan c. 40,000 years ago and outlying islands such as Okinawa (30,000 years ago) and the Solomon Islands (30,000 years ago). It is also probable that the tropical rainforests of Southeast Asia were colonised in the last 40,000-50,000 years.[557] And finally, at the end of the Pleistocene, the Tibetan Plateau, with an average altitude of 5,000 m above sea level, was also settled by humans.[558]The Palaeolithic history of Asia (and the Eurasian landmass generally) has been shaped by different types of dispersals, operating at different spatial and temporal scales and in a wide variety of environments. Rather than studying the Stone Age settlement of Asia in terms of different types of artefact assemblages, it is probably more fruitful to study how its inhabitants dispersed in response to different opportunities and challenges at different levels of physical and mental ability over the last 1.8 million years.