The effects of latitude on hominin social network maintenance

• Main Author: Pearce, E
• Other Authors: Dunbar, R, Morley, I
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: Evolutionary Anthropology; Archaeology; Arctic
• Online Access: https://ora.ox.ac.uk/objects/uuid:c51f63d2-6c07-46ec-81c8-8942afda8598

Social networks have been essential throughout hominin evolution, facilitating cooperative childrearing, transmission of cultural knowledge and the sharing of information and resources. As hominins dispersed out of Africa, these networks needed to be maintained at progressively higher latitudes. The first part of this thesis explores the impact of latitude on brain organisation and the possible implications for social cognition. I hypothesise that the lower temperatures and light levels found at higher latitudes select for larger bodies and visual systems, which in turn necessitate larger somatic and visual brain areas. Using orbit size to index eye and visual cortex size, I demonstrate a robust positive relationship between absolute latitude and orbit volume in recent humans. I show that Neanderthals, who solely inhabited high latitudes, have significantly larger orbits than contemporary anatomically modern humans (AMH), who evolved in lower latitude Africa and had only relatively recently dispersed into higher latitudes. Since Neanderthals and AMH dated 27-75kya have almost identical endocranial volumes, I argue that if a greater proportion of the Neanderthal brain was required for somatic and visual processing, this would reduce the volume of neural tissue available for other functions. Since, according to the Social Brain Hypothesis, neocortex volume is positively associated with social complexity, I propose that Neanderthals might have been limited to smaller social networks than AMH. The second part of the thesis explores the challenge of maintaining social networks across greater geographic distances at higher latitudes, where high travelling costs seem to prevent whole tribes from bonding during periodic aggregations. Using a gas model I predict that at lower latitudes daily subsistence mobility allows sufficient encounters between subgroups for the tribe to maintain connectivity, whereas in (Sub)Arctic biomes additional mechanisms are required to facilitate tribal cohesion. This may explain the apparent ...