Brain anatomy of Homo naledi
Remains of the hominin species Homo naledi discovered in the Dinaledi Chamber, South Africa, date between 236,000 and 335,000 years ago, concurrent with early ancestors of modern humans. H. naledi had small endocranial volume, suggesting a small brain, compared with other Homo species, despite sharing certain aspects of cranial anatomy with these species. To compare the brain morphology of H. naledi to that of other hominids, Ralph Holloway and colleagues created digital impressions of the interior of the skull, or endocasts, from four H. naledi cranial fragments. The inner cranial surface can preserve impressions of brain surface features. An endocast of a nearly complete H. naledi left hemisphere exhibited no fronto-orbital sulcus, a feature found in the brains of apes and Australopithecus but not in human brains. Instead, similar to modern humans and other Homo species, the H. nalediendocast exhibited a frontal operculum, formed by expansion of the frontal lobes relative to apes. H. naledi endocasts also exhibited occipital lobe asymmetry and lunate sulcus morphology similar to that seen in modern humans. The results suggest that H. naledi shared certain aspects of brain organization with modern humans, and that these features were ancestral to the Homo genus, according to the authors.