Human brain expansion

Since the evolutionary split between the human lineage and other great apes (6–7 million years ago), the human brain more than tripled in volume and increased in complexity. While early hominins such as Australopithecus afarensis (3.9 to 2.9 million years ago) had brain volumes of roughly 400–500 cubic centimeters, similar to modern chimpanzees, it was with the emergence of genus Homo around 2–2.5 million years ago that brain size began to increase more rapidly. Homo habilis (2.4 to 1.4 million years ago) had a cranial capacity of about 600–700 cc and Homo erectus (1.9 million years ago to 110 thousand years ago ) reached 900–1100 cc. In modern humans, average brain volume is approximately 1,300–1,400 cc. This expansion involved disproportionate growth of the cerebral cortex, particularly regions associated with language, abstract reasoning, planning, and social cognition. Changes in brain organization, connectivity, and prolonged developmental periods (including extended childhood) were also crucial. Together, these evolutionary modifications supported increasingly complex tool use, symbolic thought, culture, and social structures.