dr. M.C. (Mila) van den Hurk-Roozen

PhD thesis: Human social complexity - Evolutionary and methodological considerations (2024)

The ability to cognitively manage complex social environments, also termed social complexity, has been hypothesized to be an important factor in the evolution of the human brain, especially the neocortex. This is known as the social brain hypothesis. Traditional methods of studying evolutionary processes have resulted in inconsistent evidence regarding the validity of the social brain hypothesis. Recent technological and methodological advances have led to novel methods to examine both ancient and recent evolution using genetic information. The aim of this thesis is to provide a basis for future studies using genetic data to examine the evolution of human social complexity. We highlight the relevance of methodological decisions, such as the operationalization of social complexity. An example of a method studying evolution using genetic data was carried out for sociability, demonstrating how inconsistent results can follow from methodological decisions, while providing an indication that sociability genes are not more likely than average to be conserved across speciation. We examined how social complexity is associated with cognition and brain size in modern humans. We found that while operational definitions matter, social complexity measures are associated with various cognitive skills. Unexpectedly, associations between brain size and social complexity were mainly found for regions in the cerebellum instead of the neocortex. Because self-report and proxy-report of social behavior is prone to bias, passive digital technologies are proposed for the measurement of social complexity and we demonstrate how data quality and quantity affect the measurement of various behaviors using such technologies.