From DeCasien et al.:
New research has questioned or contradicted multiple long-standing claims about human brain evolution.
Contrary to the social brain hypothesis, new work suggests that ecological factors, rather than social complexity, best predict relative brain size across primate species.
Brain size does not have similar effects or cognitive implications in different phylogenetic lineages since it is associated with different mosaic structural changes.
Although the human prefrontal cortex is proportionally large, this may not represent an adaptive specialization and research emphasis on this region has distracted attention from the importance of wider neural networks.
Functional and anatomical integration, rather than developmental constraints, may primarily explain patterns of brain region size covariation across species.Abstract
Human brains are exceptionally large, support distinctive cognitive processes, and evolved by natural selection to mediate adaptive behavior. Comparative biology situates the human brain within an evolutionary context to illuminate how it has been shaped by selection and how its structure relates to evolutionary function, while identifying the developmental and molecular changes that were involved. Recent applications of powerful phylogenetic methods have uncovered new findings, some of which overturn conventional wisdom about how and why brains evolve. Here, we focus on four long-standing claims about brain evolution and discuss how new work has either contradicted these claims or shown the relevant phenomena to be more complicated than previously appreciated. Throughout, we emphasize studies of non-human primates and hominins, our close relatives and recent ancestors.The authors dispute the following common claims about human brain evolution: (Motivated readers can obtain the whole text with their detailed arguments from me.)
Claim 1. Social complexity is the primary driver of non-human primate and human brain evolution
Claim 2. Brain size has similar effects and cognitive implications across a wide range of species
Claim 3. The proportionally large human PFC reflects selection on PFC-specific functions
Claim 4. Developmental constraints play a major role in the evolution of brain structure