Anatomical differences in the brain organization between Australopithecus and early Homo based on computational neuroanatomy

Encephalization is a hallmark of human evolution, but how regional brain morphology changed during early hominin evolution remains unclear. Here, we show regional brain morphological differences between sampled Australopithecus and early Homo specimens. Using computed tomography and endocranial casts, we generated brain models for Australopithecus africanus , Homo habilis , and Homo ergaster using an anatomically homogeneous cross-species interpolation technique. Our reconstructions suggest that the posterior cerebellum was enlarged in early Homo compared with the sampled A. africanus specimens. In contrast, relative frontal lobe volume remains largely unchanged among the sampled fossils. We also identify enlargement of temporoparietal regions that, in modern humans, are associated with functions including social communication and tool use. By integrating fossil endocranial morphology with comparative neuroanatomical information from extant primates, the present approach provides a quantitative framework for generating and testing hypotheses about regional brain evolution in extinct hominins.