Biology World

Human evolution, or anthropogenesis, is the origin and evolution of Homo sapiens as a distinct species from other hominidsgreat apesand placental mammals. The study of human evolution encompasses many scientific disciplines, including physical anthropology,primatologyarchaeologylinguistics and genetics.

The term "human" in the context of human evolution refers to the genus Homo, but studies of human evolution usually include otherhominids, such as the Australopithecines. The genus Homo had diverged from the Australopithecines by about 2.3 to 2.4 million years ago in Africa. Scientists have estimated that humans branched off from their common ancestor with chimpanzees - the only other living hominins - about 5–7 million years ago. Several species of Homo evolved and are now extinct. These include Homo erectus, whichinhabited Asia, and Homo neanderthalensis, which inhabited Europe. Archaic Homo sapiens evolved between 400,000 and 250,000 years ago

The dominant view among scientists concerning the origin of anatomically modern humans is the "Out of Africa" or recent African origin hypothesis, which argues that H. sapiensarose in Africa and migrated out of the continent around 50-100,000 years ago, replacing populations of H. erectus in Asia and H. neanderthalensis in Europe. Scientists supporting the alternative multiregional hypothesis argue that H. sapiens evolved as geographically separate but interbreeding populations stemming from a worldwide migration of H. erectus out of Africa nearly 2.5 million years ago.

Genus Homo

Homo sapiens is the only non-extinct species of its genus, Homo. There were other Homo species, all of which are now extinct. While some of these other species might have been ancestors of H. 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 paucity 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 an explanation of the early variation in the genus Homo.

Based on archaeological and paleontological evidence, it has been possible to infer the ancient dietary practices of various Homo species and to study the role of diet in physical and behavioral evolution within Homo


H. habilis lived from about 2.4 to 1.4 MaH. habilis, the first species of the genus Homo, evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5–2 Ma, when it diverged from the Australopithecines. H. 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 its discoverer, Louis Leakey due to its association with stone tools. Some scientists have proposed moving this species out of Homoand into Australopithecus due to the morphology of its skeleton being more adapted to living on trees rather than to moving on two legs like H. sapiens.

Rudolfensis and Georgicus

These are proposed species names for fossils from about 1.9–1.6 Ma, the relation of which with H. habilis is not yet clear.

  • H. rudolfensis refers to a single, incomplete skull from Kenya. Scientists have suggested that this was another H. habilis, but this has not been confirmed.
  • H. georgicus, from Georgia, may be an intermediate form between H. habilis and H. erectus, or a sub-species of H. erectus.

Ergaster and Erectus

One current view of the temporal and geographical distribution of hominid populations.[21] Other interpretations differ mainly in the taxonomy and geographical distribution of hominid species.

The first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in 1891 on the Indonesian island of Java. He originally gave the material the name Pithecanthropus erectus based on its morphology that he considered to be intermediate between that of humans and apes.[22] 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 floresiensissurvived it). Often the early phase, from 1.8 to 1.25 Ma, is considered to be a separate species, H. ergaster, or it is seen as a subspecies of H. erectusHomo erectus ergaster.

In the early Pleistocene, 1.5–1 Ma, in Africa, Asia, and Europe, 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, H. erectus. In addition H. erectus was the first human ancestor to walk truly upright. 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 H. ergaster for the non-Asian forms of this group, and reserve H. erectus only for those fossils that are found in Asia and meet certain skeletal and dental requirements which differ slightly from H. ergaster

Cepranensis and Antecessor

These are proposed as species that may be intermediate between H. erectus and H. heidelbergensis.

  • H. antecessor is known from fossils from Spain and England that are dated 1.2 Ma–500 ka.
  • H. cepranensis refers to a single skull cap from Italy, estimated to be about 800,000 years old.


H. heidelbergensis (Heidelberg Man) lived from about 800,000 to about 300,000 years ago. Also proposed as Homo sapiens heidelbergensis or Homo sapiens paleohungaricus.

, and the Gawis cranium

  • H. rhodesiensis, estimated to be 300,000–125,000 years old. Most current experts believe Rhodesian Man to be within the group of Homo heidelbergensis though other designations such as Archaic Homo sapiens and Homo sapiens rhodesiensis have also been proposed.
  • In February 2006 a fossil, the Gawis cranium, was found which might possibly be a species intermediate between H. erectus and H. sapiens or one of many evolutionary dead ends. The skull from Gawis, Ethiopia, is believed to be 500,000–250,000 years old. Only summary details are known, and no peer reviewed studies have been released by the finding team. Gawis man's facial features suggest its being either an intermediate species or an example of a "Bodo man" female.


H. neanderthalensis lived from 400,000 years ago. Also proposed as Homo sapiens neanderthalensis: there is ongoing debate over whether the Neanderthal Man was a separate species, Homo neanderthalensis, or a subspecies of H. sapiens. While the debate remains unsettled, evidence from sequencing mitochondrial DNA indicates that no significant gene flow occurred between H. neanderthalensis and H. sapiens, and, therefore, the two were separate species that shared a common ancestor about 660,000 years ago. In 1997, Mark Stoneking stated: "These results [based on mitochondrial DNA extracted from Neanderthal bone] indicate that Neanderthals did not contribute mitochondrial DNA to modern humans… Neanderthals are not our ancestors." Subsequent investigation of a second source of Neanderthal DNA supported these findings. However, supporters of the multiregional hypothesis point to recent studies indicating non-African nuclear DNA heritage dating to one, although the reliability of these studies has been questioned. Competition from Homo sapiensprobably contributed to Neanderthal extinction.


H. sapiens ("sapiens" is Latin for wise or intelligent) has lived from about 250,000 years ago to the present. Between 400,000 years ago and the second interglacial period in the MiddlePleistocene, around 250,000 years ago, the trend in skull expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens. The direct evidence suggests there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa. A subsequent migration within and out of Africa eventually replaced the earlier dispersed H. erectus. This migration and origin theory is usually referred to as the recent single origin or Out of Africa theory. Current evidence does not preclude some multiregional evolution or some admixture of the migrant H. sapiens with existing Homo populations. This is a hotly debated area of paleoanthropology.

Current research has established that human beings are genetically highly homogenous; that is, the DNA of individuals is more alike than usual for most species, which may have resulted from their relatively recent evolution or the possibility of a population bottleneck resulting from cataclysmic natural events such as the Toba catastrophe. Distinctive genetic characteristics have arisen, however, primarily as the result of small groups of people moving into new environmental circumstances. These adapted traits are a very small component of the Homo sapiens genome, but include various characteristics such as skin color and nose form, in addition to internal characteristics such as the ability to breathe more efficiently in high altitudes.

H. sapiens idaltu, from Ethiopia, is a possible extinct sub-species who lived from about 160,000 years ago


H. floresiensis, which lived from approximately 100,000 to 12,000 before present, has been nicknamed hobbit for its small size, possibly a result of insular dwarfism. H. floresiensis is intriguing both for its size and its age, being a concrete example of a recent species of the genus Homo that exhibits derived traits not shared with modern humans. In other words, H. floresiensis share a common ancestor with modern humans, but split from the modern human lineage and followed a distinct evolutionary path. The main find was a skeleton believed to be a woman of about 30 years of age. Found in 2003 it has been dated to approximately 18,000 years old. The living woman was estimated to be one meter in height, with a brain volume of just 380 cm3 (considered small for a chimpanzee and less than a third of the H. sapiens average of 1400 cm3).

However, there is an ongoing debate over whether H. floresiensis is indeed a separate species. Some scientists presently believe that H. floresiensis was a modern H. sapiens suffering from pathological dwarfism. This hypothesis is supported in part, because some modern humans who live on Flores, the island where the skeleton was found, are pygmies. This coupled with pathological dwarfism could indeed create a hobbit-like human. The other major attack on H. floresiensis is that it was found with tools only associated with H. sapiens.

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