Human Evolution

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Human evolution, or anthropogenesis, is the part of biological evolution concerning the emergence of Homo sapiens sapiens as a distinct species from other hominans, great apes and placental mammals. It is the subject of a broad scientific inquiry that seeks to understand and describe how this change occurred. The study of human evolution encompasses many scientific disciplines, most notably physical anthropology, linguistics and genetics.

The term "human", in the context of human evolution, refers to the genus Homo, but studies of human evolution usually include other hominins, such as the australopithecines. The Homo genus diverged from the australopithecines about 2 million years ago in Africa. Several typological species of Homo, now extinct,(How reliable are human phylogenetic hypotheses? quote: .. existing phylogenetic hypotheses about human evolution are unlikely to be reliable [1]) evolved. These include Homo erectus, which inhabited Asia, and Homo neanderthalensis, which inhabited Europe.

Archaic Homo sapiens evolved between 400,000 and 250,000 years ago. The dominant view among scientists is the recent African origin of modern humans (RAO) that H. sapiens evolved in Africa and spread across the globe, replacing populations of H. erectus and H. neanderthalensis. Scientists supporting the alternative hypothesis on the multiregional origin of modern humans (MTO) view modern humans as having evolved as a single, widespread population from existing Homo species, particularly H. erectus. The fossil evidence is insufficient to resolve this vigorous debate, (The Origin of Humankind, ISBN 0465053130) while studies of human population genetics have largely supported a recent African Origin explanation.

Starting with H. habilis, humans began using stone tools of increasing sophistication. About 50,000 years ago, human technology and culture began to change more rapidly.

History of paleoanthropology

Paleoanthropology is the study of ancient humans based on fossil evidence, tools, and other signs of human habitation. The modern field of paleoanthropology began with the discovery of a Neanderthal skeleton in 1856, although there had been finds elsewhere since 1830.[2]

By 1859, the morphological similarity of humans to certain great apes had been discussed and argued for some time, but the idea of the biological evolution of species in general was not legitimized until Charles Darwin published On the Origin of Species in November of that year. Darwin's first book on evolution did not address the specific question of human evolution: "Light will be thrown on the origin of man and his history", was all Darwin wrote on the subject. Nevertheless, the implications of evolutionary theory were clear to contemporary readers (On the Origin of Species, [3])

Debates between Thomas Huxley and Richard Owen focused on human evolution. Huxley convincingly illustrated many of the similarities and differences between humans and apes in his 1863 book Evidence as to Man's Place in Nature. By the time Darwin published his own book on the subject, The Descent of Man, it was already a well-known interpretation of his theory, and the interpretation which made the theory highly controversial. Even many of Darwin's original supporters (such as Alfred Russel Wallace and Charles Lyell) did not like the idea that human beings could have evolved their impressive mental capacities and moral sensibilities through natural selection.

Since the time of Carolus Linnaeus, scientists have considered the great apes to be the closest relatives of human beings because they look very similar. In the 19th century, they speculated that the closest living relatives of humans are chimpanzees. Based on the natural range of these creatures, they surmised that humans share a common ancestor with other African great apes and that fossils of these ancestors would be found in Africa. It is now accepted by virtually all biologists that humans are not only similar to the great apes but, in fact, are great apes.

It was only in the 1920s that such fossils were discovered in Africa. In 1925, Raymond Dart described Australopithecus africanus.[4] The type specimen was the Taung Child, an australopithecine infant discovered in a cave. This cave, in Taung, South Africa, was being mined for raw materials used to make concrete. The child's remains were a remarkably well-preserved tiny skull and an endocranial cast of the individual's 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.

Another 20 years would pass before Dart's claims were taken seriously, following the discovery of more fossils that resembled his find. The prevailing view of the time was that a large brain evolved before bipedality. It was thought that intelligence on par with modern humans was a prerequisite to bipedalism.

The australopithecines are now thought to be immediate ancestors of the genus Homo, the group to which modern humans belong. Both australopithecines and Homo sapiens are part of the tribe Hominini, but recent data has brought into doubt the position of A. africanus as a direct ancestor of modern humans; it may well have been a dead-end cousin. The australopithecines were originally classified as either gracile or robust. The robust variety of Australopithecus has since been reclassified as Paranthropus, although it is still regarded as a subgenus of Australopithecus by some authors.

In the 1930s, when the robust specimens were first described, the Paranthropus genus was used. During the 1960s, the robust variety was moved into Australopithecus. The recent trend has been back to the original classification as a separate genus.[5]

Table of Human Evolution

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Further Reading

  • Flinn, M. V., Geary, D. C., & Ward, C. V. (2005). Ecological dominance, social competition, and coalitionary arms races: Why humans evolved extraordinary intelligence. Evolution and Human Behavior, 26, 10-46. Full text.PDF (345 KB)
  • Rozsa L 2008. The rise of non-adaptive intelligence in humans under pathogen pressure. Medical Hypotheses, 70, 685-690.
  • Wolfgang Enard et al. (2002-08-22). "Molecular evolution of FOXP2, a gene involved in speech and language". Nature 418: 870.
  • DNA Shows Neandertals Were Not Our Ancestors
  • J. W. IJdo, A. Baldini, D. C. Ward, S. T. Reeders, R. A. Wells (October 1991). "Origin of human chromosome 2: An ancestral telomere-telomere fusion" (PDF). Genetics 88: 9051–9055. http://www.pnas.org/cgi/reprint/88/20/9051.pdf. —two ancestral ape chromosomes fused to give rise to human chromosome 2.
  • Ovchinnikov, et al. (2000). "Molecular analysis of Neanderthal DNA from the Northern Caucasus". Nature 404: 490. doi:10.1038/35006625.
  • Heizmann, Elmar P J, Begun, David R (2001). "The oldest Eurasian hominoid". Journal of Human Evolution 41 (5): 463. doi:10.1006/jhev.2001.0495.
  • JBS Haldane (1955). "Origin of Man". Nature 176 (169).
  • BBC: Finds test human origins theory. 2007-08-08 Homo habilis and Homo erectus are sister species that overlapped in time.

External links

See Also