Recent African origin of modern humans

From Wikipedia, the free encyclopedia
  (Redirected from Out of Africa theory)
Jump to: navigation, search
Map of Homo sapiens migrations, starting from the possible location of Y-chromosomal Adam (yellow star) in central Africa.

In paleoanthropology, the recent African origin of modern humans, also called the "Out of Africa" theory (OOA), the "recent single-origin hypothesis" (RSOH), "replacement hypothesis," or "recent African origin model" (RAO), is the most widely accepted model of the geographic origin and early migration of anatomically modern humans.[1][2][3][4][5][6] The theory argues for the African origins of modern humans, who left Africa in a single wave of migration which populated the world, replacing older human species.[7][8][9]

A first dispersal took place between 130,000–115,000 years ago via northern Africa, but died out or retreated,[10][11][12][13][14] though Chinese researchers question this extinction and claim the presence of modern humans in China at least 80,000 years ago.[15] A second dispersal took place via the so-called Southern Route,[16] which followed the southern coastline of Asia, and colonized Australia by around 50,000 years ago. Europe was populated by an early offshoot which settled the Near East and Europe (post-Toba hypothesis).[17][8][9][10]

The major competing hypothesis of this single origin (monogenesis) theory is the multiregional origin of modern humans, which envisions a wave of Homo sapiens migrating earlier from Africa and interbreeding with local Homo erectus populations in multiple regions of the globe.[18][19]

Early Homo sapiens[edit]




Homo sapiens idaltu, found at site Middle Awash in Ethiopia, lived about 160,000 years ago.[21] It is the oldest known anatomically modern human and classified as an extinct subspecies.[22]


Fossil finds outside Africa[edit]

Fossils of early Homo sapiens were found in Qafzeh cave in Israel and have been dated to 80,000 to 100,000 years ago.[25] A fossil of a modern human dated to 54,700 years ago was found in Manot Cave in Israel, named Manot 1,[26][27] though the dating was questioned by Groucutt et al. (2015).[28] Fossils from Lake Mungo, Australia have been dated to about 42,000 years ago.[29][30] The Tianyuan cave remains in China's Liujiang region have a probable date range between 38,000 and 42,000 years ago. The Tianyuan specimens are most similar in morphology to Minatogawa Man, modern humans dated between 17,000 and 19,000 years ago and found on Okinawa Island, Japan.[31][32]

Movement out of Africa[edit]

Map of early human migrations[33]
1. Homo sapiens
2. Neanderthals
3. Early hominids

The accepted[10] theory is that there were two dispersals.[17][34] an early one via northern Africa,[10] and a second one which replaced the early homin populations.

The first dispersal took place between 130,000–115,000 years ago via northern Africa, but died out or retreated.[10][11][12][13][14] Chinese researchers question this extinction, claiming that modern humans were present in China already 80,000 years ago.[15]

A second dispersal took place via the so-called Southern Route,[16] either before[35] or after[17][8][9] the Toba event, which happened between 69,000 and 77,000 years ago.[35] This dispersal followed the southern coastline of Asia, crossing about 250 kilometres (155 mi) of sea, and colonized Australia by around 50,000 years ago. According to this theory, Europe was populated either by a migration out of India, which was repopulated from southeast Asia after the Toba-event (pre-Toba hypothesis),[36] or by an early offshoot which settled the Near East and Europe (post-Toba hypothesis).[17][8][9][10]

Early northern Africa dispersal[edit]

The early northern Africa dispersal took place between 130,000–115,000 years ago.[10] The discovery of stone tools in the United Arab Emirates in 2011 indicated the presence of modern humans between 100,000 and 125,000 years ago.[11][37] An increasing number of researchers think that "long-neglected North Africa"[12][38] may have been the original home of the first modern humans to migrate out of Africa.[13][14]

Fossils of early Homo sapiens were found in Qafzeh cave in Israel and have been dated to 80,000 to 100,000 years ago. These humans seem to have either become extinct or retreated back to Africa 70,000 to 80,000 years ago, possibly replaced by southbound Neanderthals escaping the colder regions of ice age Europe.[39] Hua Liu et al. analyzed autosomal microsatellite markers dates to c. 56,000±5,700 years ago mtDNA evidence. He interprets the paleontological fossil of early modern human from Qafzeh cave as an isolated early offshoot that retracted back to Africa.[25]

According to Kuhlwilm et al. (2016) Altai Neaderthalers received gene flow from modern humans circa 100,000 years ago, from humans which split off from other modern humans circa 200,000 years ago.[40][41] Kuhlwilm et al. conclude that "the ancestors of Neanderthals from the Altai Mountains and early modern humans met and interbred, possibly in the Near East, many thousands of years earlier than previously thought."[40] According to co-author Ilan Gronau, "this actually complements archaeological evidence of the presence of early modern humans out of Africa around and before 100 ka by providing the first genetic evidence of such populations."[41]

Chinese research questions the extinction of this early dispersal. Shen et al. (2002) have dated Liujang Man to 111,000 to 139,000 years before the present.[42] Liu et al. (2015) claim that modern human teeth have been found in China dating to at least 80 000 years ago.[15][43]

Southern Route dispersal[edit]

Red Sea crossing
Main article: Coastal migration

Coastal route[edit]

By some 70,000 years ago,[16] a part of the bearers of mitochondrial haplogroup L3 migrated from East Africa into the Near East. It has been estimated that from a population of 2,000 to 5,000 individuals in Africa,[44] only a small group, possibly as few as 150 to 1,000 people, crossed the Red Sea.[45]

The group that crossed the Red Sea travelled along the coastal route around the coast of Arabia and Persia until reaching India, which appears to be the first major settling point.[46] Geneticist Spencer Wells says that the early travellers followed the southern coastline of Asia, crossed about 250 kilometres (155 mi) of sea, and colonized Australia by around 50,000 years ago. The Aborigines of Australia, Wells says, are the descendants of the first wave of migrations.[47]

Today at the Bab-el-Mandeb straits, the Red Sea is about 20 kilometres (12 mi) wide, but 50,000 years ago sea levels were 70 m (230 ft) lower (owing to glaciation) and the water was much narrower. Though the straits were never completely closed, they were narrow enough and there may have been islands in between to have enabled crossing using simple rafts.[48][49] Shell middens 125,000 years old have been found in Eritrea,[50] indicating the diet of early humans included seafood obtained by beachcombing.

Dating: pre-or post-Toba[edit]

The dating of the Southern Dispersal is a matter of dispute.[35] It may have happened either pre- or post-Toba, a catastrophic volcanic eruption that took place between 69,000 and 77,000 years ago at the site of present-day Lake Toba. Stone tools discovered below the layers of ash disposed in India may point to a pre-Toba dispersal, but the exact source of these tools is disputed.[35]

An indication for post-Toba is haplo-group L3, that originated before the dispersal of humans out of Africa, and can be dated to 60,000–70,000 years ago, "suggesting that humanity left Africa a few thousand years after Toba."[35] Yet, new research showing slower than previously thought genetic mutations in human DNA published in 2012, indicating a revised dating for the migration of between 90,000 and 130,000 years ago.[51]

Peopling of Europe[edit]


According to Martin Meredith, members of one branch of Homo sapiens left Africa at some point between 125,000 and 60,000 years ago, and over time these humans replaced other populations of the genus Homo such as Neanderthals and Homo erectus.[7]

According to Stephen Oppenheimer, Europe was populated by a migration out of India, which was repopulated from southeast Asia after the Toba-event.[36]


According to Macaulay et al. (2005) an early offshoot from the southern disposal with haplogroup N followed the Nile from East Africa, heading northwards and crossing into Asia through the Sinai.[17] This group then branched in several directions, some moving into Europe and others heading east into Asia.[17] This hypothesis is supported by the relatively late date of the arrival of modern humans in Europe as well as by both archaeological and DNA evidence.[17]

Based on an analysis of 55 complete human mitochondrial genomes (mtDNAs) of hunter-gatherers, Posth et al. (2016) argue for a "rapid single dispersal of all non-Africans less than 55,000 years ago."[9][52]

Multiple dispersals[edit]

Several authors have argued for multiple dispersals.[53][28] Spencer Wells, in The Journey of Man (2002) describes two waves of migration, first the southern coastal route, then a northern migration into Europe[54] at circa 45,000 years ago.[55][note 1] This possibility is ruled out by Macauly et al. (2005)[57][55] and Posth et al. (2016),[9] arguing for a single coastal dispersal.[55]

Genetic reconstruction[edit]

Eve and Adam[edit]

Two pieces of the human genome are quite useful in deciphering human history: mitochondrial DNA and the Y chromosome. These are the only two parts of the genome that are not shuffled about by the evolutionary mechanisms that generate diversity with each generation: instead, these elements are passed down intact. According to the hypothesis, all people alive today have inherited the same mitochondria[58] from a woman who lived in Africa about 160,000 years ago.[59][60] She has been named Mitochondrial Eve. All men living today have inherited their Y chromosomes from a man who lived 140,000–500,000 years ago, probably in Africa. He has been named Y-chromosomal Adam. Based on comparisons of non-sex-specific chromosomes with sex-specific ones, it is now estimated that more men than women participated in the out-of-Africa exodus of early humans.[61]

Haplogroup L and migrations within Africa[edit]




L3 and single dispersal[edit]

Some researchers think that only a few people left Africa in a single migration that went on to populate the rest of the world,[8] based on the fact that only descendents of L3 are found outside Africa.

Of all the lineages present in Africa only the female descendants of one lineage, mtDNA haplogroup L3, are found outside Africa. If there had been several migrations, one would expect descendants of more than one lineage to be found outside Africa. L3's female descendants, the M and N haplogroup lineages, are found in very low frequencies in Africa (although haplogroup M1 populations are very ancient and diversified in North and Northeast Africa) and appear to be more recent arrivals. A possible explanation is that these mutations occurred in East Africa shortly before the exodus and became the dominant haplogroups after the exodus from Africa through the founder effect. Alternatively, the mutations may have arisen shortly after the exodus from Africa.

Africans, Eurasians and East Asians[edit]


In June 2009, an analysis of genome-wide SNP data from the International HapMap Project (Phase II) and CEPH Human Genome Diversity Panel samples was published.[65] Those samples were taken from 1138 unrelated individuals.[65]


The study determined that most ethnic group differences can be attributed to genetic drift, with modern African populations having greater genetic diversity than the other two genetic groups, and modern Eurasians somewhat more than modern East Asians.[66] The study suggested that natural selection may shape the human genome much more slowly than previously thought, with factors such as migration within and among continents more heavily influencing the distribution of genetic variations.[67]


Southern Route and haplogroups M and N[edit]

Results from mtDNA collected from aboriginal Malaysians called Orang Asli and the creation of a phylogentic tree indicate that the hapologroups M and N share characteristics with original African groups from approximately 85,000 years ago and share characteristics with sub-haplogroups among coastal southeast Asian regions, such as Australasia, the Indian Subcontinent, and throughout continental Asia, which had dispersed and separated from its African origins approximately 65,000 years ago. This southern coastal dispersion would have occurred before the dispersion through the Levant approximately 45,000 years ago.[17] 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.[69][70] 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).

The group that crossed the Red Sea travelled along the coastal route around the coast of Arabia and Persia until reaching India, which appears to be the first major settling point.[46] Haplogroup 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.[46] Sixty percent of the Indian population belong to Haplogroup M.




Admixture of archaic and modern humans[edit]

Genetic testing in the last decade has revealed that several now extinct archaic human species may have interbred with modern humans. These species have been claimed to have left their genetic imprint in different regions across the world: Neanderthals in all humans except Sub-Saharan Africans, Denisova hominin in Australasia (for example, Melanesians, Aboriginal Australians and some Negritos) and there could also have been interbreeding between Sub-Saharan Africans and an as-yet-unknown hominin (possibly remnants of the ancient species Homo heidelbergensis). However, the rate of interbreeding was found to be relatively low (1–10%) and other studies have suggested that the presence of Neanderthal or other archaic human genetic markers in modern humans can be attributed to shared ancestral traits originating from a common ancestor 500,000 to 800,000 years ago.[76][77][78][79][80] Still, a study published in March 2016 provided fresh evidence of interbreeding between modern humans and hominins, including Denisovans and Neanderthals, indicating that such interbreeding occurred at multiple times during human history.[81]

History of the theory[edit]

Further information: Timeline of human evolution



Charles Darwin[edit]


Charles Darwin was one of the first to propose common descent of living organisms, and among the first to suggest that all humans had in common ancestors who lived in Africa.[82] Darwin first suggested the "Out of Africa" hypothesis after studying the behaviour of African apes, one of which was displayed at the London Zoo. The anatomist Thomas Huxley had also supported the hypothesis and suggested that African apes have a close evolutionary relationship with humans.[83] These views were however opposed by the German biologist Ernst Haeckel, who was a proponent of the Out of Asia theory. Haeckel argued that humans were more closely related to the primates of Southeast Asia and rejected Darwin’s hypothesis of Africa.[84][85]



— Charles Darwin, Descent of Man[87]


Monogenism and Mitochondrial Eve[edit]



Mungo Man[edit]

In 2000, the mitochondrial DNA (mtDNA) sequence of "Mungo Man 3" (LM3) of ancient Australia was published.[90][91] This work was later questioned[92] and explained by W. James Peacock, leader of the team who sequenced Mungo man's aDNA.[93] In addition, a large-scale genotyping analysis of aboriginal Australians, New Guineans, Southeast Asians and Indians in 2013 showed close genetic relationship between Australian, New Guinean, and the Mamanwa people, with divergence times for these groups estimated at 36,000 y ago. Further, substantial gene flow was detected between the Indian populations and aboriginal Australians, indicating an early "southern route" migration out of Africa, and arrival of other populations in the region by subsequent dispersal. This basically opposes the view that there was an isolated human evolution in Australia.[94]

According to Smith et al. (2003), the results indicated that Mungo Man was an extinct subspecies that diverged before the most recent common ancestor of contemporary humans, and supports the multiregional origin of modern humans hypothesis.[95]

Competing hypotheses[edit]


See also[edit]




  3. ^ "This week in Science: Out of Africa Revisited". Science. 308 (5724): 921. 13 May 2005. doi:10.1126/science.308.5724.921g. 
  7. ^ a b Meredith 2011.
  8. ^ a b c d e "Both Australian Aborigines and Europeans Rooted in Africa". Retrieved 11 January 2011. 
  9. ^ a b c d e f Posth 2016.
  10. ^ a b c d e f g Out of Africa Hypothesis
  15. ^ a b c Liu 2015.
  16. ^ a b c K. Kris Hirst, Southern Dispersal Route – Early Modern Humans Leave Africa
  17. ^ a b c d e f g h Macaulay 2005.
  23. ^ "Ancestral tools". 1 August 1999. Retrieved 11 January 2011. 
  24. ^ "Middle to upper paleolithic transition". Retrieved 11 January 2011. 
  25. ^ a b Liu H, Prugnolle F, Manica A, Balloux F; Prugnolle; Manica; Balloux (August 2006). "A geographically explicit genetic model of worldwide human-settlement history". Am. J. Hum. Genet. 79 (2): 230–7. doi:10.1086/505436. PMC 1559480free to read. PMID 16826514. 
  26. ^ Hershkovitz 2015.
  27. ^ "55,000-Year-Old Skull Fossil Sheds New Light on Human Migration out of Africa". Science News. Retrieved 2 February 2015. 
  28. ^ a b c Groucutt 2015.
  34. ^ Beyin 2011.
  35. ^ a b c d e Appenzeller 2015.
  36. ^ a b The Bradshaw Foundation and Stephen Oppenheimer, Journey of Mankind. The peopling of the world.
  37. ^ "Humans may have left Africa earlier than thought". Retrieved 14 June 2011. 
  39. ^ Finlayson 2009, p. 68.
  40. ^ a b Kuhlwilm 2016.
  41. ^ a b Dienekes'Anthropology Blog, Ancestors of Eastern Neandertals admixed with modern humans 100 thousand years ago
  42. ^ Shen 2002.
  43. ^ Dieneks' Anthropology Blog, Modern humans in China ~80,000 years ago (?)
  44. ^ Zhivotovsky; Rosenberg, NA; Feldman, MW; et al. (2003). "Features of Evolution and Expansion of Modern Humans, Inferred from Genomewide Microsatellite Markers". American Journal of Human Genetics. 72 (5): 1171–86. doi:10.1086/375120. PMC 1180270free to read. PMID 12690579. 
  49. ^ Beyin, Amanuel (February 2011). "Upper Pleistocene Human Dispersals out of Africa: A Review of the Current State of the Debate". International Journal of Evolutionary Biology. 2011 (615094): 1–17. doi:10.4061/2011/615094. 
  51. ^ Catherine Brahic (24 November 2012). "Our True Dawn". New Scientist. Reed Business Information (2892): 34–7. ISSN 0262-4079. 
  52. ^ Dienekes' Anthroplogy Bog, mtDNA from 55 hunter-gatherers across 35,000 years in Europe
  53. ^ Posth 2016, p. 1.
  54. ^ Wells 2002.
  55. ^ a b c Bradshaw Foundation, Human Migration
  56. ^ Young McChesney 2015.
  57. ^ Macauly 2005.
  60. ^ Vigilant L, Stoneking M, Harpending H, Hawkes K, Wilson AC; Stoneking; Harpending; Hawkes; Wilson (September 1991). "African populations and the evolution of human mitochondrial DNA". Science. 253 (5027): 1503–7. Bibcode:1991Sci...253.1503V. doi:10.1126/science.1840702. PMID 1840702. 
  64. ^ Macaulay, V; Hill, C; Achilli, A; Rengo, C; Clarke, D; Meehan, W; Blackburn, J; Semino, O; Scozzari, R; et al. (2005). "Single, Rapid Coastal Settlement of Asia Revealed by Analysis of Complete Mitochondrial Genomes". Science. 308 (5724): 1034–6. doi:10.1126/science.1109792. PMID 15890885. 
  66. ^ a b c Brown, David (22 June 2009). "Among Many Peoples, Little Genomic Variety". The Washington Post. Retrieved 25 June 2009. 
  67. ^ "Geography And History Shape Genetic Differences In Humans". Science Daily. 7 June 2009. Retrieved 25 June 2009. 
  68. ^ Yu, Ning; et al. (May 2002). "Larger Genetic Differences Within Africans Than Between Africans and Eurasians". Genetics. Genetics Society of America. Retrieved 7 April 2013. 
  70. ^ "A single origin, several dispersal hypothesis". 29 October 2004. Retrieved 11 January 2011. 
  76. ^ [1]
  77. ^
  78. ^ [2]
  79. ^ The Human Stew
  80. ^ . doi:10.1371/journal.pgen.1002837.  Missing or empty |title= (help)
  81. ^ Zimmer, Carl (17 March 2016). "Humans Interbred With Hominins on Multiple Occasions, Study Finds". The New York Times. Retrieved 17 March 2016. 
  86. ^ Bowler 2003, p. 213
  89. ^ "Allan Wilson: Revolutionary Evolutionist". New Zealanders Heroes. 
  91. ^ Australia Challenges Out-of-Africa Theory ABC News 9 January 2003
  94. ^ Pugach I, Delfin F, Gunnarsdóttir E, Kayser M, Stoneking M; Delfin; Gunnarsdóttir; Kayser; Stoneking (2013). "Genome-wide data substantiate Holocene gene flow from India to Australia". Proc Natl Acad Sci U S A. 110 (5): 1803–1808. Bibcode:2013PNAS..110.1803P. doi:10.1073/pnas.1211927110. PMC 3562786free to read. PMID 23319617. 


Further reading[edit]



External links[edit]

Overview with multiple maps
Human evolution