Africa's population is the youngest amongst all the continents;[4][5] the median age in 2012 was 19.7, when the worldwide median age was 30.4.[6] Algeria is Africa's largest country by area, and Nigeria by population. Africa, particularly central Eastern Africa, is widely accepted as the place of origin of humans and the Hominidae clade (great apes), as evidenced by the discovery of the earliest hominids and their ancestors, as well as later ones that have been dated to around seven million years ago, including Sahelanthropus tchadensis, Australopithecus africanus, A. afarensis, Homo erectus, H. habilis and H. ergaster – with the earliest Homo sapiens (modern human) found in Ethiopia being dated to circa 200,000 years ago.[7] Africa straddles the equator and encompasses numerous climate areas; it is the only continent to stretch from the northern temperate to southern temperate zones.[8]