Humans belong to the species Homo sapiens. Earlier humans had a heavier bone structure and a smaller brain capacity. Modern humans are lighter in build and have high foreheads with a large brain capacity.
According to the Smithsonian Museum of Natural History, humans belong to the genus Homo. Earlier species belonging to this genus were Homo habilis and Homo erectus. The only species belonging to the genus is Homo sapiens, and modern man actually belongs to the subspecies Homo sapiens sapiens.
Modern man may have evolved from the species Australopithecus afarensis, the first species to stand upright. Homo habilis evolved from the australopithecines about 2.5 million years ago. Homo erectus arose 1.8 million years ago, but it died out 250,000 years ago. Homo sapiens originated about 300,000 years ago, but these archaic humans were somewhat structurally different from modern humans.