Homo

Homo is the genus of great apes that includes modern humans and species closely related to them. The genus is estimated to be about 2.3 to 2.4 million years old, possibly having evolved from australopithecine ancestors, with the appearance of Homo habilis. Specifically, H. habilis is assumed to be the direct descendant of Australopithecus garhi, which lived about 2.5 million years ago. However, in May 2010 H. gautengensis was discovered, a species believed to be even older than H. habilis.

The most salient physiological development between the two species is the increase in cranial capacity, from about 450 cm3 (27 cu in) in A. garhi to 600 cm3 (37 cu in) in H. habilis. Within the Homo genus, cranial capacity again doubled from H. habilis through Homo ergaster or H. erectus to Homo heidelbergensis by 0.6 million years ago. The cranial capacity of H. heidelbergensis overlaps with the range found in modern humans.

The advent of Homo was thought to coincide with the first evidence of stone tools (the Oldowan industry), and thus by definition with the beginning of the Lower Palaeolithic; however, recent evidence from Ethiopia now places the earliest evidence of stone tool usage at before 3.39 million years ago. The emergence of Homo coincides roughly with the onset of Quaternary glaciation, the beginning of the current ice age.

All species of the genus except Homo sapiens (modern humans) are extinct. Homo neanderthalensis, traditionally considered the last surviving relative, died out about 24,000 years ago, though recent discoveries suggest that two other species, Homo floresiensis and the Red Deer Cave people, may have lived much more recently. The other extant Homininae—the chimpanzees and gorillas—have a limited geographic range. In contrast, the evolution of humans is a history of migrations and admixture. According to genetic studies, modern humans bred with "at least two groups" of ancient humans: Neanderthals and Denisovans. Humans repeatedly left Africa to populate Eurasia and finally the Americas, Oceania, and the rest of the world.

According to scientists in June 2012, early hominids, such as Australopithecus sediba, may have lived in savannas but ate fruits and other foods from the forest - behavior similar to modern-day savanna chimpanzees.