Human evolution is the evolutionary process leading up to the appearance of anatomically modern humans. The topic usually covers the evolutionary history of primates, in particular the genus Homo, and the emergence of Homo sapiens as a distinct species of hominids (or "great apes") rather than studying the evolutionary history that led to primates. The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, paleontology, ethology, linguistics, evolutionary psychology, embryology and genetics. Genetic studies show that primates diverged from other mammals about 85 million years ago, in the Late Cretaceous period, and the earliest fossils appear in the Paleocene, around 55 million years ago.The Hominidae family diverged from the Hylobatidae (gibbon) family 15–20 million years ago, and around 14 million years ago, the subfamily Ponginae (orangutans) diverged from the Hominidae family. Bipedalism is the basic adaption of the hominin line. 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 bipedal, arose somewhat later, and the early bipedals eventually evolved into the australopithecines, and later into the genus Homo. The earliest documented members of the genus Homo are Homo habilis, which evolved around 2.8 million years ago and it is arguably the earliest species for which there is positive evidence of 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 began, and with the arrival of Homo erectus in the fossil record, cranial capacity had doubled to 850 cm3. This increase in human brain size is equivalent to every generation having an additional 125,000 neurons more than their parents. It is believed that these species were the first to use fire and complex tools. Homo erectus and Homo ergaster were also the first of the hominin line to leave Africa, and these species spread through Africa, Asia, and Europe between 1.3 to 1.8 million years ago. According to the recent African origin of modern humans theory, modern humans evolved in Africa possibly from Homo heidelbergensis, Homo rhodesiensis or Homo antecessor and migrated out of the continent some 50,000 to 100,000 years ago, gradually replacing local populations of Homo erectus, Denisova hominins, Homo floresiensis and Homo neanderthalensis. Archaic Homo sapiens, the forerunner of anatomically modern humans, evolved between 400,000 and 250,000 years ago.Recent DNA evidence suggests that several haplotypes of Neanderthal origin are present among all non-African populations, and Neanderthals and other hominins, such as Denisovans, may have contributed up to 6% of their genome to present-day humans, suggestive of a limited inter-breeding between these species.Anatomically modern humans evolved from archaic Homo sapiens in the Middle Paleolithic, about 200,000 years ago. The transition to behavioral modernity with the development of symbolic culture, language, and specialized lithic technology happened around 50,000 years ago according to many anthropologists although some suggest a gradual change in behavior over a longer time span. During the 1960s and 1970s, hundreds of fossils were found, particularly in East Africa in the regions of the Olduvai Gorge and Lake Turkana. The driving force in the East African researches was the Leakey family, with Louis Leakey and his wife Mary Leakey, and later their son Richard and daughter in-law Meave being among the most successful fossil hunters and palaeoanthropologists. From the fossil beds of Olduvai and Lake Turkana they amassed fossils of australopithecines, early Homo and even Homo erectus. These finds cemented Africa as the cradle of humankind. In the 1980s, Ethiopia emerged as the new hot spot of palaeoanthropology as "Lucy," the most complete fossil member of the species Australopithecus afarensis, was found by Donald Johanson in Hadar in the desertic Middle Awash region of northern Ethiopia. This area would be the location of many new hominin fossils, particularly those uncovered by the team headed by Tim D. White in the 1990s, such as Ardipithecus ramidus. The genetic revolution in studies of human evolution started when Vincent Sarich and Allan Wilson measured the strength of immunological cross-reactions of blood serum albumin between pairs of creatures, including humans and African apes (chimpanzees and gorillas).

• published: 17 Sep 2015
• views: 1