The primitive brain of early Homo
Human brains are larger than and structurally different from the brains of the great apes. Ponce de León et al. explored the timing of the origins of the structurally modern human brain (see the Perspective by Beaudet). By comparing endocasts, representations of the inner surface of fossil brain cases, from early Homo from Africa, Georgia, and Southeast Asia, they show that these structural innovations emerged later than the first dispersal of the genus from Africa, and were probably in place by 1.7 to 1.5 million years ago. The modern humanlike brain organization emerged in cerebral regions thought to be related to toolmaking, social cognition, and language. Their findings suggest that brain reorganization was not a prerequisite for dispersals from Africa, and that there might have been more than one long-range dispersal of early Homo.Science, this issue p. 165; see also p. 124The brains of modern humans differ from those of great apes in size, shape, and cortical organization, notably in frontal lobe areas involved in complex cognitive tasks, such as social cognition, tool use, and language. When these differences arose during human evolution is a question of ongoing debate. Here, we show that the brains of early Homo from Africa and Western Asia (Dmanisi) retained a primitive, great ape–like organization of the frontal lobe. By contrast, African Homo younger than 1.5 million years ago, as well as all Southeast Asian Homo erectus, exhibited a more derived, humanlike brain organization. Frontal lobe reorganization, once considered a hallmark of earliest Homo in Africa, thus evolved comparatively late, and long after Homo first dispersed from Africa.