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While human evolution begins with the last common ancestor of all life, it generally refers to the evolutionary history of primates and in particular the genus Homo, including the emergence of Homo sapiens as a distinct species of hominids ("great apes"). The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, linguistics, embryology and genetics.
Primate evolution likely began in the late Cretaceous, 85 Ma (million years ago) by genetic studies and no later than the Paleocene by the fossil record 55 Ma. The family Hominidae, or Great Apes, diverged from the Hylobatidae family 15-20 Ma. Around 14 Ma the Ponginae or orangutans diverged from the Hominidae family. Later the gorilla and chimpanzee would diverge from the lineage leading to the genus Homo, the latter around 5-6 Ma. Modern humans evolved from the last common ancestor of the Hominini and the species Australopithecines some 2.3-2.4 million years ago in Africa.
In the Hominini tribe, several species and subspecies of Homo evolved and are now extinct or introgressed, and only one species remains. Examples include Homo erectus (which inhabited Asia, Africa, and Europe) and Neanderthals (either Homo neanderthalensis or Homo sapiens neanderthalensis) (which inhabited Europe and Asia). Archaic Homo sapiens, the forerunner of anatomically modern humans, evolved between 400,000 and 250,000 years ago. Anatomically modern humans evolved from archaic Homo sapiens in the Middle Paleolithic, about 200,000 years ago. Behaviorally modern humans developed around 50,000 years ago according to many, although some view modern behavior as beginning with the emergence of anatomically modern humans.
One view among scientists concerning the origin of anatomically modern humans is the recent African origin of modern humans hypothesis (the "recent single-origin hypothesis" or "recent out-of-Africa" model), which posits that Homo sapiens arose in Africa and migrated out of the continent some 50,000 to 100,000 years ago, replacing populations of Homo erectus in Asia and Neanderthals in Europe. An alternative multiregional hypothesis posits that Homo sapiens evolved as geographically separate but interbreeding populations stemming from the worldwide migration of Homo erectus out of Africa nearly 2.5 million years ago. 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.
History of ideas
Anaximander postulated that man was, originally, similar to a different animal, that is, a fish. 
The word homo, the name of the biological genus to which humans belong, is Latin for "human". It was chosen originally by Carolus Linnaeus in his classification system. The word "human" is from the Latin humanus, the adjectival form of homo. The Latin "homo" derives from the Indo-European root *dhghem, or "earth".
Linnaeus and other scientists of his time also considered the great apes to be the closest relatives of humans due to morphological and anatomical similarities. The possibility of linking humans with earlier apes by descent only became clear after 1859 with the publication of Charles Darwin's On the Origin of Species. This argued for the idea of the evolution of new species from earlier ones. Darwin's book did not address the question of human evolution, saying only that "Light will be thrown on the origin of man and his history".
The first debates about the nature of human evolution arose between Thomas Huxley and Richard Owen. Huxley argued for human evolution from apes by illustrating many of the similarities and differences between humans and apes, and did so particularly in his 1863 book Evidence as to Man's Place in Nature. However, many of Darwin's early supporters (such as Alfred Russel Wallace and Charles Lyell) did not agree that the origin of the mental capacities and the moral sensibilities of humans could be explained by natural selection. Darwin applied the theory of evolution and sexual selection to humans when he published The Descent of Man in 1871.
A major problem at that time was the lack of fossil intermediaries. Despite the 1891 discovery by Eugène Dubois of what is now called Homo erectus at Trinil, Java, it was only in the 1920s when such fossils were discovered in Africa, that intermediate species began to accumulate. In 1925 Raymond Dart described Australopithecus africanus. The type specimen was the Taung Child, an Australopithecine infant which was discovered in a cave. The child's remains were a remarkably well-preserved tiny skull and an endocranial cast of the brain. Although the brain was small (410 cm³), its shape was rounded, unlike that of chimpanzees and gorillas, and more like a modern human brain. Also, the specimen showed short canine teeth, and the position of the foramen magnum was evidence of bipedal locomotion. All of these traits convinced Dart that the Taung baby was a bipedal human ancestor, a transitional form between apes and humans.
The classification of humans and their relatives has changed considerably since the 1950s. For instance; gracile Australopithecines were thought to be ancestors of the genus Homo, the group to which modern humans belong. Both Australopithecines and Homo sapiens are part of the tribe Hominini.
Data collected during the 1970s suggests that Australopithecines were a diverse group and that A. africanus may not be a direct ancestor of modern humans. Reclassification of Australopithecines that originally were split into either gracile or robust varieties has put the latter into its own genus, Paranthropus. Taxonomists place humans, Australopithecines and related species in the same family as other great apes, in the Hominidae. Richard Dawkins in his book The Ancestor's Tale proposes that robust Australopithecines: Paranthropus, are the ancestors of gorillas, whereas some of the gracile australopithecus are the ancestors of chimpanzees, the others being human ancestors (see Homininae).
Progress during the 1980s and 1990s in DNA sequencing, specifically mitochondrial DNA (mtDNA) and then Y-chromosome DNA advanced the understanding of human origins. Sequencing mtDNA and Y-DNA sampled from a wide range of indigenous populations revealed ancestral information relating to both male and female genetic heritage. Aligned in genetic tree differences were interpreted as supportive of a recent single origin. Analysis have shown a greater diverse of DNA pattern throughout Africa, consistent with the idea that Africa is the ancestral home of mitochondrial Eve and Y-chromosomal Adam. The word homo, the name of the biological genus to which humans belong, is Latin for "human". It was chosen originally by Carolus Linnaeus in his classification system. The word "human" is from the Latin humanus, the adjectival form of homo. The Latin "homo" derives from the Indo-European root *dhghem, or "earth".
The evidence for human evolution is found in many fields of natural science. Much of this evidence is in the fossil record, although genetics is now playing an ever-increasing and complementary role. The studies of ontogeny, phylogeny and especially evolutionary developmental biology of both vertebrates and invertebrates offer considerable insight into the evolution of all life, including how humans evolved. The specific study of the origin and life of humans is anthropology, with paleoanthropology of particular interest.
In hominids, the fossil record shows the progressive straightening of the spine, the increase in brain volume, changes in facial features towards being more gracile, and a reduction in the muscles of mastication with a concomitant change in dentition.
The tail becomes incorporated into the pelvis as the sacrum in higher primates. All vertebrates have a tail at one point in their development; in humans, it is present for a period of four weeks, during stages 14 to 22 of human embryogenesis. Humans have a non-functional third eyelid, the plica semilunaris. Humans also have external ear muscles, which animals use to swivel and manipulate their ears (independently of their head) to focus their hearing on particular sounds. Humans still have remnants of such muscles, but they are now feeble and now are capable only of slightly wiggling the ear.
The plantaris muscle also serves as evidence of human evolution. The plantaris muscle is used by animals in gripping and manipulating objects with their feet, for example apes, who can use their feet as well as their hands for gripping. Humans have a corresponding muscle, but it is now so underdeveloped that it is often taken out by doctors when they need tissue for reconstruction in other parts of the body. The muscle is so unimportant to the human body that 9% of humans are now born without it. Other evidence includes Jacobson's organ, which is a part of animal anatomy, and which could figure in the sexual prehistory of humans. This organ, located in the nasal passage, detects pheromones (the chemical that triggers sexual desire, alarm, or information about food trails). This organ allows some animals to track others for sex and to warn of potential dangers. Humans are born with the Jacobson’s organ, but in early development its abilities dwindle to a point that it is useless. In some cases, structures once identified as vestigial simply had an unrecognized function. Wisdom teeth serve as evidence of evolution; human ancestors ate a lot of plants, and they needed to eat them quickly enough that they could eat a sufficient amount in one day to get the necessary nutrition. For this reason they had an extra set of molars to make the larger mouth more productive. This was particularly essential as the body lacked the ability to sufficiently digest cellulose. As evolution made its selections, human dietary patterns changed, the jaw became smaller, and the third molar was not as necessary.
Evolution of the great apes
Evolutionary history of the primates can be traced back 65 million years. The oldest known primate-like mammal species, the Plesiadapis, came from North America, but they were widespread in Eurasia and Africa during the tropical conditions of the Paleocene and Eocene.
David Begun concluded that early primates flourished in Eurasia and that a lineage leading to the African apes and humans, including Dryopithecus, migrated south from Europe or Western Asia into Africa. The surviving tropical population of primates, which is seen most completely in the upper Eocene and lowermost Oligocene fossil beds of the Faiyum depression southwest of Cairo, gave rise to all living species—lemurs of Madagascar, lorises of Southeast Asia, galagos or "bush babies" of Africa, and the anthropoids: platyrrhine or New World monkeys, catarrhines or Old World monkeys, the great apes, and humans.
The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya Rift Valley, dated to 24 million years ago. Its ancestry is thought to be species related to Aegyptopithecus, Propliopithecus, and Parapithecus from the Fayum, at around 35 million years ago. In 2010, Saadanius was described as a close relative of the last common ancestor of the crown catarrhines, and tentatively dated to 29–28 million years ago, helping to fill an 11-million-year gap in the fossil record.
In the early Miocene, about 22 million years ago, the many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the earliest Old World Monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa. The presence of other generalized non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene. The youngest of the Miocene hominoids, Oreopithecus, is from coal beds in Italy that have been dated to 9 million years ago.
Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) diverged from Great Apes some 18-12 million years ago, and that of orangutans (subfamily Ponginae) diverged from the other Great Apes at about 12 million years; there are no fossils that clearly document the ancestry of gibbons, which may have originated in a so-far-unknown South East Asian hominoid population, but fossil proto-orangutans may be represented by Ramapithecus from India and Griphopithecus from Turkey, dated to around 10 million years ago.
Divergence of the human lineage from other Great Apes
Species close to the last common ancestor of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and then the chimpanzees (genus Pan) split off from the line leading to the humans; human DNA is approximately 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms (see human evolutionary genetics). The fossil record of gorillas and chimpanzees is limited. Both poor preservation (rain forest soils tend to be acidic and dissolve bone) and sampling bias probably contribute to this problem.
Other hominines likely adapted to the drier environments outside the equatorial belt, along with antelopes, hyenas, dogs, pigs, elephants, and horses. The equatorial belt contracted after about 8 million years ago. Fossils of these hominans - the species in the human lineage following divergence from the chimpanzees - are relatively well known.
The earliest are Sahelanthropus tchadensis (7 Ma) and Orrorin tugenensis (6 Ma), followed by:
Homo sapiens is the only extant species of its genus, Homo. While some other, extinct Homo species might have been ancestors of Homo sapiens, many were likely our "cousins", having speciated away from our ancestral line. There is not yet a consensus as to which of these groups should count as separate species and which as subspecies. In some cases this is due to the dearth of fossils, in other cases it is due to the slight differences used to classify species in the Homo genus. The Sahara pump theory (describing an occasionally passable "wet" Sahara Desert) provides one possible explanation of the early variation in the genus Homo.
Based on archaeological and paleontological evidence, it has been possible to infer, to some extent, the ancient dietary practices of various Homo species and to study the role of diet in physical and behavioral evolution within Homo.
H. habilis and H. gautengensis
Homo habilis lived from about 2.4 to 1.4 Ma. Homo habilis evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5–2 Ma, when it diverged from the Australopithecines. Homo habilis had smaller molars and larger brains than the Australopithecines, and made tools from stone and perhaps animal bones. One of the first known hominids, it was nicknamed 'handy man' by discoverer Louis Leakey due to its association with stone tools. Some scientists have proposed moving this species out of Homo and into Australopithecus due to the morphology of its skeleton being more adapted to living on trees rather than to moving on two legs like Homo sapiens.
It was considered to be the first species of the genus Homo until May 2010, when a new species, Homo gautengensis was discovered in South Africa, that most likely arose earlier than Homo habilis.
H. ergaster and H. erectus
The first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in 1891 on the Indonesian island of Java. He originally named the material Pithecanthropus erectus based on its morphology, which he considered to be intermediate between that of humans and apes. Homo erectus (H erectus) lived from about 1.8 Ma to about 70,000 years ago (which would indicate that they were probably wiped out by the Toba catastrophe; however, Homo erectus soloensis and Homo floresiensis survived it). Often the early phase, from 1.8 to 1.25 Ma, is considered to be a separate species, Homo ergaster, or it is seen as a subspecies of Homo erectus, Homo erectus ergaster.
In the early Pleistocene, 1.5–1 Ma, in Africa some populations of Homo habilis are thought to have evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, Homo erectus.  This was made possible by the evolution of locking knees and a different location of the foramen magnum (the hole in the skull where the spine enters). They may have used fire to cook their meat.
A famous example of Homo erectus is Peking Man; others were found in Asia (notably in Indonesia), Africa, and Europe. Many paleoanthropologists now use the term Homo ergaster for the non-Asian forms of this group, and reserve Homo erectus only for those fossils that are found in Asia and meet certain skeletal and dental requirements which differ slightly from H. ergaster.
This article uses material from the Wikipedia article "Human evolution", which is released under the Creative Commons Attribution-Share-Alike License 3.0.