Human Evolution: ' Prehistory to Present '

Human evolution is the evolutionary process that led to the emergence of anatomically modern humans. The topic typically focuses on the evolutionary history of the primates-in particular the genus Homo, and the emergence of Homo sapiens as a distinct species of the hominids (or "great apes")-rather than studying the earlier history that led to the primates. The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, paleontology, neurobiology, ethology, linguistics, evolutionary psychology, embryologyand genetics. Genetic studies show that primates diverged from other mammals about 85million years ago, in the Late Cretaceous period, and the earliest fossils appear in the Paleocene, around 55million years ago. Within the Hominoidea (apes) superfamily, the Hominidaefamily diverged from the Hylobatidae (gibbon) family some 15-20 million years ago; African great apes (subfamily Homininae) diverged fromorangutans (Ponginae) about 14million years ago; the Hominini tribe (humans, Australopithecines and other extinct biped genera, and chimpanzees) parted from the Gorillini tribe (gorillas) about 8 million years ago; and, in turn, the subtribes Hominina (humans and biped ancestors) and Panina (chimps) separated about 7.5 million years ago. The basic adaptation of the hominin line is bipedalism. The earliest bipedal hominin is considered to be either Sahelanthropus or Orrorin; alternatively, either Sahelanthropus or Orrorin may instead be the last shared ancestor between chimps and humans. Ardipithecus, a full biped, arose somewhat later, and the early bipeds eventually evolved into the australopithecines, and later into the genus Homo. The earliest documented representative of the genus Homo is Homo habilis, which evolved around 2.8 million years ago, and is arguably the earliest species for which there is positive evidence of the use of stone tools. The brains of these early hominins were about the same size as that of a chimpanzee, although it has been suggested that this was the time in which the human SRGAP2 gene doubled, producing a more rapid wiring of the frontal cortex. During the next million years a process of rapid encephalization occurred, and with the arrival of Homo erectus and Homo ergaster in the fossil record, cranial capacity had doubled to 850 cm3. (Such an increase in human brain size is equivalent to each generation having 125,000 more neurons than their parents.) It is believed