Human Evolution

Human evolution refers to the evolutionary process leading up to the appearance of modern humans. While it began with the last common ancestor of all life, the topic usually only 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"). The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, linguistics, embryology and genetics.

According to genetic studies, 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 family Hominidae diverged from the Hylobatidae (Gibbon) family 15-20 million years ago, and around 14 million years ago, the Ponginae (orangutans), diverged from the Hominidae family. Bipedalism is the basic adaption of the Hominin line, and the earliest bipedal Hominin is considered to be either Sahelanthropus or Orrorin, with Ardipithecus, a full bipedal, coming somewhat later. The gorilla and chimpanzee diverged around the same time, about 4-6 million years ago, and either Sahelanthropus or Orrorin may be our last shared ancestor with them. The early bipedals eventually evolved into the Australopithecines and later the genus Homo.

The earliest documented members of the genus Homo are Homo habilis which evolved around 2.3 million years ago. Homo habilis is the first species for which we have positive evidence of use of stone tools. The brains of these early homininas were about the same size as that of a chimpanzee. During the next million years a process of encephalization began, and with the arrival of Homo erectus in the fossil record, cranial capacity had doubled to 850cc. Homo erectus and Homo ergaster were the first of the hominina to leave Africa, and these species spread through Africa, Asia, and Europe between 1.3 to 1.8 million years ago. It is believed that these species were the first to use fire and complex tools. According to the Recent African Ancestry theory, modern humans evolved in Africa possibly from Homo heidelbergensis and migrated out of the continent some 50,000 to 100,000 years ago, replacing local populations of Homo erectus 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 hominids, such as Denisova hominin may have contributed up to 6% of their genome to present-day humans. 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.