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Single-origin hypothesis

From Academic Kids

In paleoanthropology, the single-origin hypothesis (or Out-of-Africa model) is one of two accounts of the origin of anatomically modern humans, Homo sapiens. (The other theory is the multiregional hypothesis.)

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Pre-modern (non-sapiens) hominids

Because of the scarcity of fossils and the discovery of important new finds every few years, researchers disagree about the details and sometimes even basic elements of human evolutionary history. While they have revised this history several times over the last decades, researchers currently agree that the oldest named species of the genus Homo, Homo habilis, evolved in Africa around two million years ago, and that members of the genus migrated "out of Africa" somewhat later. The descendants of these ancient migrants, which probably included Homo erectus, have become known through fossils uncovered far from Africa, such as those of "Peking man" and "Java man". The Homo neanderthalensis is also considered a descendant of early migrants.

"Modern" humans

According to the single-origin model, however, every species of the genus Homo but one, Homo sapiens, was driven extinct. This species had evolved in eastern Africa between 100,000 and 200,000 years ago and, some time afterwards, in a relatively recent exodus, began colonizing the rest of the world. According to the single-origin model, these more recent migrants did not interbreed with the scattered descendants of earlier exoduses. For this reason, the model is sometimes called the "replacement scenario". In support of it, advocates have drawn from both fossil and DNA evidence, in particular from mitochondrial and Y-chromosome DNA sequences. Research on the X chromosome rejects the pure Out of Africa model (http://dienekes.blogspot.com/2005/06/research-on-x-chromosome-rejects-pure.html) claims to be the first genetic evidence against Out of Africa.

Missing image
Human_mtDNA_migration.png
Map of early human migrations according to mitochondrial population genetics (numbers are millennia before present); The letters on the arrows represent groups of people belonging to the same haplogroup. Haplogroups are a type of genetic categorization that groups people together base on shared variation in their mitochondrial DNA.

Single exodus from Africa?

Assuming only relatively recent migrants from Africa gave rise to today's non-African humans, was there more than one migration that left descendants? (for example, one each via the north and south ends of the Red Sea)

  • Stephen Oppenheimer is one proponent of a single exodus
  • John Hawks in Playing games with dates (http://johnhawks.net/weblog/reviews/genetics/macaulay_southern_route_mtdna_2005.html) criticizes current presentations of the idea

Multiregional hypothesis

The opponents of a single origin argue that interbreeding indeed occurred, and that the characteristics of modern humans, including those that have been and still are perceived by some to distinguish races, could only be the result of genetic contributions from several earlier lineages that evolved semi-independently in different parts of the world. This is the "multiregional hypothesis".

Proponents of the Single-origin hypothesis

See also

Further reading

  • Stringer, Chris and Robin McKie, African Exodus, ISBN 0-7126-7307-5 (paperback), 1996.
  • Cavalli-Sforza, Luigi Luca and Francesco Cavalli-Sforza, The Great Human Diasporas – The History of Diversity and Evolution (Italian original Chi Siamo: La Storia della Diversit`a Umana), ISBN 0-201-44231-0 (paperback), 1993.
  • Foley, Robert, Humans Before Humanity, ISBN 0-631-20528-4 (paperback), 1995.
  • Spencer Wells. The Journey of Man: A Genetic Odyssey (2003)
  • Brian Sykes. The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry (2002)

Reference

  • "Modern Men Trace Ancestry to African Migrants", Science magazine, 2001 [1] (http://www.sciencemag.org/cgi/content/full/292/5519/1051b)zh:单地起源说
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