Recent African origin of modern humans 247704 225971976 2008-07-16T07:30:26Z Master z0b 3021738 [[Image:Migration map4.png|thumb|350px|right|Map of [[early human migrations]] according to [[Mitochondrial DNA|mitochondrial]] [[population genetics]] ]] In [[paleoanthropology]], the recent African origin of modern humans is one of two accounts of the origin of anatomically modern humans, ''[[Homo sapiens sapiens]]''. The theory is known popularly as the '''(Recent) Out-of-Africa''' model, and academically also as the '''recent single-origin hypothesis''' ('''RSOH'''), '''Replacement Hypothesis''' or '''Recent African Origin''' ('''RAO''') model. According to the theory, anatomically modern humans evolved solely in [[Africa]], between 200,000 and 100,000 years ago, with members of one branch leaving Africa by 60,000 years ago and replacing all earlier human populations such as [[Neanderthals]] and [[Homo erectus]]. The hypothesis originated in the 1980s based on a study of [[mitochondrial DNA]], and its proponents have since presented evidence based on [[physical anthropology]] as well. The recent single origin of modern humans in [[East Africa]] is currently the mainstream position held within the scientific community. <ref>Hua Liu, et al. [http://dx.doi.org/10.1086/505436 A Geographically Explicit Genetic Model of Worldwide Human-Settlement History]. The American Journal of Human Genetics, volume 79 (2006), pages 230–237,</ref> Alternative scenarios claim a [[multiregional origin of modern humans]], including claims of [[interbreeding of Cro-Magnon and Neanderthals]] or other earlier hominids (e.g. [[Homo Erectus]], see [[Hybrid-origin]]). Some of these claims push back the original "out of Africa" migration to 2 million<ref>http://www.actionbioscience.org/evolution/johanson.html Origins of Modern Humans: Multiregional or Out of Africa? By Donald Johanson</ref><ref>http://discovermagazine.com/2002/aug/featafrica Discover: Not Out of Africa, Alan Thorne's challenging ideas about human evolution</ref> years ago. ==History of the theory== [[Charles Darwin]] was one of the first to suggest that all humans had a common ancestor who lived in Africa. In the [[Descent of Man]] he writes: {{cquote|In each great region of the world the living [[mammals]] are closely related to the extinct species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the [[gorilla]] and [[chimpanzee]]; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.<ref>[http://www.literature.org/authors/darwin-charles/the-descent-of-man/chapter-06.html The descent of man Chapter 6 - On the Affinities and Genealogy of Man]</ref>}} The prediction was highly insightful because at the time, in 1871, there were hardly any human fossils of ancient hominids available. Almost fifty years later Darwin was vindicated, as anthropologists began finding numerous fossils of ancient hominids all over Africa ([[list of hominina fossils]]). In 19th century [[anthropology]], "[[monogenism]]" was opposed by "[[polygenism]]", the idea that the various human [[Race (classification of human beings)|races]] had evolved independently out of archaic hominids. Such views were largely obsolete by the mid 20th century, although there were isolated proponents in the later 20th century such as [[Carleton S. Coon|Carleton Coon]] who hypothesized as late as 1962 that ''Homo sapiens'' arose five separate times from ''Homo erectus'' in five separate places.<ref> Jackson Jr., John P. (2001). ''[http://comm.colorado.edu/jjackson/research/coon.pdf"InWays Unacademical": The Reception of Carleton S. Coon's The Origin of Races'']</ref> With the advent of [[archaeogenetics]] in the 1990s, it became possible to date the "out of Africa" migration with some confidence. The question whether there may have been admixture ([[hybrid-origin|hybridization]]) of ''Homo erectus'' and ''Homo sapiens'' remains under debate. ==Early Homo sapiens== {{main|Early Homo sapiens}} ''[[Homo sapiens]]'' has lived from about 250,000 years ago to the present. Between 400,000 years ago and the second interglacial period in the Middle [[Pleistocene]], around 250,000 years ago, the trend in [[Cranial capacity|cranial expansion]] and the elaboration of stone tool technologies developed, providing evidence for a transition from ''[[Homo erectus|H. erectus]]'' to ''H. sapiens''. In the RAO scenario, migration within and out of Africa eventually replaced the earlier dispersed ''H. erectus''. ''[[Homo sapiens idaltu]]'', from Ethiopia, lived from about 160,000 years ago. It is the oldest known anatomically modern human. Fossils of modern humans were found in a cave in [[Israel]] at [[Qafzeh]] and have been dated to 100,000 years ago. However these humans seem to have either gone extinct or retreated back to Africa 70,000 to 80,000 years ago, possibly replaced by south bound Neanderthals escaping the colder regions of ice age Europe.{{Fact|date=December 2007}} All other fossils of fully modern humans outside of Africa have been dated to more recent times. The next oldest fossil of modern humans outside of Africa are those of [[Mungo Man]] found in Australia and have been dated to about 42,000 years ago.<ref>[http://www.mnh.si.edu/anthro/humanorigins/ha/sap.htm human origins by the Museum of natural history]</ref> Beginning about 100,000 years ago evidence of more sophisticated technology and artwork begins to emerge and by 50,000 years ago fully [[Behavioral modernity|modern behaviour]] becomes more prominent. By this time the ritual burying of the dead is noted. Stone tools show regular patterns that are reproduced or duplicated with more precision. Tools made of bone and antler appear for the first time.<ref>[http://www.handprint.com/LS/ANC/stones.html Ancestral tools]</ref><ref>[http://www.wsu.edu/~rquinlan/mptoup.htm Middle to upper paleolithic transition]</ref> These new changes are suggestive of more advanced behaviour and scientists attribute these changes to the [[Origin of language|development of language]]. ==Genetic reconstruction== {{see|Archaeogenetics|Early human migrations}} Two pieces of the [[human genome]] are particularly useful in deciphering human history. One is the [[mitochondrial DNA]] and the other is the [[Y chromosome]]. These are the only two parts of the genome that are not shuffled about by the evolutionary mechanisms which generate diversity with each generation. Hence the Mitochondrial DNA and the Y chromosome are passed down generation to generation intact. According to the hypothesis, all 6.7 billion people alive today have inherited the same Mitochondria from one woman who lived in Africa about 200,000 years ago<ref>Cann, R. L., Stoneking, M., Wilson, A. C. (1987) Mitochondrial DNA and human evolution. Nature. Vol. 325. Pp. 31-36.</ref><ref>Vigilant, L., Stoneking, M., Harpending, H., Hawkes, K., Wilson, A. C. (1991) African Populations and the Evolution of Human Mitochondrial DNA. Science. Vol. 253. Pp 1503-1507</ref>; she has been named [[Mitochondrial Eve]]. All men today have inherited their Y chromosomes from a man who lived 60,000 years ago, probably in Africa. He has been named [[Y-chromosomal Adam]]. ===Mitochondrial DNA=== {{see|Human mitochondrial DNA haplogroup}} [[Image:Map-of-human-migrations.jpg|thumb|right|350px|One model of human migration based on Mitochondrial DNA]] The first lineage to branch off from Eve is [[Haplogroup L1 (mtDNA)|L1]]. This haplogroup is found in high proportions among the [[san people|San]] and the [[Mbuti]] people.<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1288201 mtDNA Variation in the South African Kung and Khwe]</ref> These groups branched off early in human history and have remained relatively isolated genetically since. [[Haplogroup L2 (mtDNA)|Haplogroups L2]] and [[Haplogroup L3 (mtDNA)|L3]] are descendents of L1 and are largely confined to Africa. The macro haplogroups [[Haplogroup M (mtDNA)|M]] and [[Haplogroup N (mtDNA)|N]], which are the lineages of the rest of the world outside Africa, descended from L3. ===Y-chromosomal DNA=== {{main|Human Y-chromosome DNA haplogroups|Haplogroup F (Y-DNA)}} The mutations defining macro-haplogroup [[Haplogroup CR (Y-DNA)|CR]] (all Y haplogroups except [[Haplogroup A (Y-DNA)|A]] and [[Haplogroup B (Y-DNA)|B]]) predate the "Out of Africa" migration, its descendent macro-group [[Haplogroup DE (Y-DNA)|DE]] being confined to Africa. The mutations that distinguish Haplogroup [[Haplogroup C (Y-DNA)|C]] from all other descendants of CR have occurred some 60,000 years ago, shortly after the first Out of Africa migration. [[Haplogroup F (Y-DNA)|Haplogroup F]] originated some 45,000 years ago, either in [[North Africa]] (in which case it would point to a second wave of out-of-Africa migration) or in [[South Asia]]. More than 90% of males not native to Africa are descended in direct male line from the first bearer of haplogroup F. ==Exodus from Africa== [[Image:Red Sea2.png|thumb|right|200px|[[Red Sea]]]] Some 70 millennia ago, a part of the bearers of mitochondrial haplogroup [[Haplogroup L3 (mtDNA)|L3]] migrated from [[East Africa]] into the [[Near East]]. Some scientists believe that only a few people left Africa in a single migration that went on to populate the rest of the world<ref>[http://news.softpedia.com/news/Both-Aborigines-and-Europeans-Rooted-in-Africa-54225.shtml Both Australian Aborigines and Europeans Rooted in Africa]</ref>. It has been estimated that from a population of 2,000 to 5,000 in Africa, only a small group of possibly 150 people crossed the Red Sea. This is because, of all the lineages present in Africa, only the daughters of one lineage, L3, are found outside Africa. Had there been several migrations one would expect more than one African lineage outside Africa. L3's daughters, the M and N lineages, are found in very low frequencies in Africa and appear to be recent arrivals. A possible explanation is that these mutations occurred in East Africa shortly before the exodus and by the [[founder effect]] became the dominant haplogroups after the exodus from Africa. Alternatively, the mutations may have arisen shortly after the exodus from Africa. Other scientists propose a Multiple Dispersals Model, in which there were two migrations out of Africa, one across the Red Sea travelling along the coastal regions to India (the Coastal Route), which would be represented by Haplogroup M. Another group of migrants with Haplogroup N followed the Nile from East Africa, heading northwards and crossing into [[Asia]] through the [[Sinai]]. This group then branched in several directions, some moving into Europe and others heading east into Asia. This hypothesis attempts to explain why Haplogroup N is predominant in Europe and why Haplogroup M is absent in Europe. Evidence of the coastal migration is hypothesized to have been destroyed by the rise in sea levels during the [[Holocene]] epoch.<ref>[http://www.biomedcentral.com/1471-2156/2/13/comments/comments A single origin, several dispersal hypothesis]</ref><ref>[http://www.human-evol.cam.ac.uk/Projects/sdispersal/sdispersal.htm Searching for traces of the Southern Dispersal], by Dr. Marta Mirazón Lahr, et. al.</ref> Alternatively, a small European founder population that initially expressed both Haplogroup M and N could have lost Haplogroup M through random genetic drift resulting from a [[bottleneck]] (i.e. a [[founder effect]]). [[Image:Single origin multiple dispersals.jpg|thumb|right|350px|Single origin from Africa but with multiple dispersals out of Africa of [[Haplogroup M (mtDNA)|haplogroup M]] and [[Haplogroup N (mtDNA)|haplogroup N]]]] Today at the [[Bab-el-Mandeb straits]] the [[Red Sea]] is about 12 miles (20 kilometres) wide but 50,000 years ago it was much narrower and sea levels were 70 meters lower. Though the straits were never completely closed, there may have been islands in between which could be reached using simple rafts. Shell [[middens]] 125,000 years old have been found in [[Eritrea]] indicating the diet of early humans was sea food obtained by [[beachcombing]]. ==Subsequent expansion== {{main|Early human migrations}} From the Near East, these populations spread east to [[Paleolithic South Asia|South Asia]] by 50 millennia ago, and on to [[Prehistoric Australia|Australia]] by 40 millennia ago, ''Homo sapiens'' for the first time colonizing territory never reached by ''Homo erectus''. [[Paleolithic Europe|Europe]] was reached by [[Cro-Magnon]] some 40 millennia ago. East Asia ([[Prehistoric Korea|Korea]], [[Japanese Paleolithic|Japan]]) was reached by 30 millennia ago. It is disputed whether subsequent [[Models of migration to the New World|migration to North America]] took place around 30 millennia ago, or only considerably later, around 14 millennia ago. The group that crossed the Red Sea travelled along the coastal route around the coast of Arabia and Iran until reaching India, which appears to be the first major settling point. M is found in high frequencies along the southern coastal regions of [[Pakistan]] and India and it has the greatest diversity in India, indicating that it is here where the mutation may have occurred.<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=516768#B3 Most of the extant mtDNA boundaries in South and Southwest Asia were likely shaped during the initial settlement of Eurasia by anatomically modern humans<!-- Bot generated title -->]</ref> 60% of the Indian population belong to Haplogroup M. The indigenous people of the [[Andaman Islands]] also belong to the M lineage. The Andamanese are thought to be offshoots of some of the earliest inhabitants in Asia because of their long isolation from mainland Asia. They are evidence of the coastal route of early settlers that extends from India along the coasts of [[Thailand]] and Indonesia all the way to [[Papua New Guinea]]. Since M is found in high frequencies in highlanders from New Guinea as well, and both the Andamanese and New Guineans have dark skin and [[natural hair|Afro-textured hair]], some scientists believe they are all part of the same wave of migrants who departed across the Red Sea ~60,000 years ago. Notably, the findings of Harding et. al.(2000, p 1355) show that, at least with regard to dark [[skin color]], the haplotype background of Papua New Guineans at [[MC1R]] (one of a number of genes involved in melanin production) is identical to that of Africans (barring a single silent mutation). Thus, although these groups are distinct from Africans at other loci (due to drift, bottlenecks, etc), it is evident that selection for the dark [[skin color]] trait likely continued (at least at MC1R) following the exodus. This would support the hypothesis that suggests that the original migrants from Africa resembled pre-exodus Africans (at least in skin color), and that the present day remnants of this ancient phenotype can be seen among contemporary Africans, Andamanese and New Guineans. Others suggest that their physical resemblance to Africans could be the result of [[convergent evolution]].<ref>[http://ehl.santafe.edu/ruhlen.htm Evolution of Human Languages<!-- Bot generated title -->]</ref><ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=378623 genetic origins of the Andaman Islanders]</ref><ref>[http://hpgl.stanford.edu/publications/CB_2002_p1-18.pdf Genetic affinities of the Andaman Islanders]</ref>. From [[Saudi Arabia]] to India the proportion of haplogroup M increases eastwards: in eastern India, M outnumbers N by a ratio of 3:1. However, crossing over into East Asia, Haplogroup N reappears as the dominant lineage. M is predominant in South East Asia but amongst [[Indigenous Australians]] N reemerges as the more common lineage. This discontinuous distribution of Haplogroup N from Europe to Australia has confounded scientists attempting to trace migratory routes.<ref>[http://www.genome.org/cgi/content/full/13/7/1600 Mitochondrial Genome Variation and Evolutionary History of Australian and New Guinean Aborigines]</ref>. However, it is well known that such distributions can be explained by way of [[founder's effect]] and its accompanying [[bottleneck]]ing, which result in irregular distributions in genetic patterning due to what amounts to random sampling from a relatively small initial population (i.e. those who migrated out of Africa). ==Competing hypotheses== {{main|Multiregional origin of modern humans}} {{see|Interbreeding of Cro-Magnon and Neanderthals}} The multi-regional (''hybrid-origin'') hypothesis proposes admixture of archaic ''Homo sapiens'' subspecies resulting in [[hybrid (biology)|hybrid]]s that gave rise to the world's [[Race (classification of human beings)|races]]. This means that proponents reject the assumption of a [[species barrier]] between ''[[Homo erectus]]'' and ''Homo sapiens'' and date the first "out of Africa" migration of ''Homo sapiens'' subspecies to 2 million years ago. The recent migration out of Africa 60,000 years ago would then have brought previously isolated subspecies into renewed contact, resulting in a hybrid ''Homo sapiens sapiens'', who was superior to both its ancestor subspecies due to what is commonly termed [[hybrid vigour]]. Proponents argue that very strong genetic similarities among all humans do not prove recent common ancestry, but rather reflect the interconnectedness of human populations around the world, resulting in relatively constant gene flow (Thorne and Wolpoff 1992). [[Erik Trinkaus]] is a proponent of hybridization of [[Cro-Magnon]] ''H. sapiens'' with ''[[Homo neanderthalensis]]'' around 30,000 years ago. These theories are based largely on archaeological and fossil evidence. They are not widely recognized, opponents citing the lack of DNA evidence. While the hybrid-origin scenario at present cannot be ruled out with certainty, more extreme proposals, known as [[polygenism]], were a topic of academic debate in later 19th century, but are obsolete today as historical examples of [[scientific racism]]. ==See also== *[[Behavioral modernity]] *[[Early human migrations]] *[[Hofmeyr Skull]] *[[Hybrid-origin]] *[[Identical ancestors point]] *[[Mitochondrial Eve]] *[[Most recent common ancestor]] *[[Multiregional hypothesis]] *[[Paleolithic]] *[[Sahara pump theory]] *[[Y-chromosomal Adam]] ==References== {{reflist|2}} ==Further reading== {{citation style}} * [http://www.sciencemag.org/cgi/content/full/292/5519/1051b Modern Men Trace Ancestry to African Migrants], ''[[Science (journal)|Science]]'', [[11 May]] [[2001]] * Underhill et al. (2001). "The phylogeography of Y chromosome binary haplotypes and the origins of modern human populations" ''Ann. Hum. Genet.'' '''65:''' 43-62. [http://www.human-evol.cam.ac.uk/Members/Lahr/pubs/AHG-65-01.pdf PDF]. Retrieved 25 July 2007. * [http://news.bbc.co.uk/2/hi/science/nature/323657.stm Neanderthals 'mated with modern humans'], ''[[BBC News]]'', [[21 April]] [[1999]] * [http://news-info.wustl.edu/tips/page/normal/6349.html New analysis shows three human migrations out of Africa - Replacement theory 'demolished'], ''[[Washington University in St. Louis]]'', [[2 February]] [[2006]] *{{anchor|Harding}}{{cite journal|first=Rosalind M.|last=Harding|coauthors=Eugene Healy, Amanda J. Ray, Nichola S. Ellis, Niamh Flanagan, Carol Todd, Craig Dixon, Antti Sajantila, Ian J. Jackson, Mark A. Birch-Machin, and Jonathan L. Rees|year=2000|title=Evidence for variable selective pressures at MC1R|journal=American Journal of Human Genetics|volume=66|pages=1351–1361|doi=10.1086/302863}} * Long and Kittles (2003). "Human genetic variation and the nonexistence of human races" ''Human Biology'', '''75:''' 449-471. [http://muse.jhu.edu/journals/human_biology/v075/75.4long.pdf PDF]. Retrieved 10 January 2007. * {{cite journal | author = Risch, N., Burchard, E., Ziv, E. and Tang, H. | year = 2002 | month = | title = Categorization of humans in biomedical research: genes, race and disease | journal = Genome Biology | volume = 3 | issue = 7 | pages = comment2007.2001 - comment2007.2012 | id = | doi = 10.1186/gb-2002-3-7-comment2007 }} * Tishkoff, S. and Kidd, K. ''Implications of biogeography of human populations for 'race' and medicine Nature Genetics'' '''36:''' S21 - S27 (2004) {{doi|doi:10.1038/ng1438}} * Cavalli-Sforza, [[Luigi Luca Cavalli-Sforza|Luigi Luca]] and Francesco Cavalli-Sforza, ''The Great Human Diasporas &ndash; The History of Diversity and Evolution'' (Italian original ''Chi Siamo: La Storia della Diversit`a Umana''), ISBN 0-201-44231-0 (paperback), 1993. * Crow, Tim J, Editor ''The Speciation of Modern Homo Sapiens'', ISBN 0-19-726311-9 (paperback) 2002. * Foley, Robert, ''Humans Before Humanity'', ISBN 0-631-20528-4 (paperback), 1995. * Olsen, Steve, ''Mapping Human History: Discovering the past through our genes'' ISBN 0618352104 2002 * Oppenheimer, Stephen, ''The Real Eve: Modern Man's Journey Out of Africa'', ISBN 0-7867-1192-2 (Hardcover), 2003. * Stringer, Chris and Robin McKie, ''African Exodus'', ISBN 0-7126-7307-5 (paperback), 1996. * Sykes, Brian, ''[[The Seven Daughters of Eve]]: The Science That Reveals Our Genetic Ancestry'' (2002) ISBN 0552152188 * Wade, Nicholas, '' Before the Dawn: Recovering the Lost History of Our Ancestors'' (2006) ISBN 1594200793 * Wells, Spencer, ''The Journey of Man: A Genetic Odyssey'' (2003) ISBN 069111532X * Wells, Spencer, ''Deep Ancestry: Inside the Genographic Project'' (2006) ISBN 0792262158 * [http://www.sciencedaily.com/releases/2007/07/070718140829.htm "New Research Proves Single Origin Of Humans In Africa,"] Science Daily, July 19, 2007, retrieved July 19, 2007 *[http://www.timesonline.co.uk/tol/news/world/africa/article2617296.ece Climate change led mankind out of Africa] *[http://www.sciencedaily.com/releases/2007/10/071008171121.htm Ancient African Megadroughts May Have Driven Human Evolution Out Of Africa] *[http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/02/22/MN5RV6L1C.DTL DNA studies trace human migration from Africa] retrieved February 21, 2008 ==External links== *[http://cambridgedna.com/genealogy-dna-ancient-migrations-slideshow.php An mtDNA view of the peopling of the world by Homo sapiens] * [https://www5.nationalgeographic.com/genographic/atlas.html National Geographic: Atlas of the Human Journey] * [http://www.bradshawfoundation.com/journey/ Bradshaw Foundation: The Journey of Mankind] *[http://www.nhm.ac.uk/nature-online/life/human-origins/webcast-humanoriginsvid/human-origins.html Natural History Museum - Video] *[http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020057&ct=1&SESSID=5fab197c67cb062db1c5353ad98bf3c6 "No evidence of Neandertal mtDNA contribution to early modern humans"] 2004 article by [[Svante Pääbo]] et al. 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