A million years of hominin sociality and cognition: Acheulean bifaces in the Hunsgi-Baichbal Valley, India

The Acheulean spans over 1.5 million years of human history, during which time brain size increases from around 850 cubic centimetres in early Homo erectus, to 1300 cubic centimetres in Homo heidelbergensis, with body size remaining approximately constant. This book analyzes behaviour at the well-preserved locale of Isampur Quarry, India, in order to discern some of the socio-cognitive capacities of early Acheulean hominins. Experimental, artefactual and spatial evidence are used to reconstruct hominin behaviour at Isampur Quarry, which is unusual in having the entire reduction sequence of biface manufacture preserved at a single locale. The Isampur Quarry evidence suggests that Acheulean hominins had a propensity for imitation and shared intentionality. These abilities were the basis for an iconic gestural communication system, which was used in co-ordinating co-operative activities. Isampur is situated in a regional context by comparing its bifaces with those from five other sites in the same valley, including one around 1 million years younger. Comparison with a further four well known sites from around the world provide a global context for Isampur. Bifaces are compared using three-dimensional geometric morphometrics to determine which sites have bifaces with similar morphologies. The study suggests that the dominant pattern of inter-site variation in biface shape is chronological, with bifaces become smaller, thinner and relatively wider over time. A broader comparative study using published metric data confirms this pattern and suggests that the trend corresponds to the increase in brain size during the Acheulean. It is concluded that there is a chronological trajectory of increasing motor skill and the hierarchical organisation of dynamic action plans during the Acheulean. This evidence is used to support the hypothesis that, during the Acheulean, there was a transition from an iconic gestural communication system, to symbolic and syntactic vocal language