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Recent African origin of modern humans
Recent African origin of modern humans
Recent African origin of modern humans
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Successive dispersals (labeled in years before present) of
  Homo erectus greatest extent (yellow)
  Homo neanderthalensis greatest extent (ochre)
  Homo sapiens (red)
Expansion of early modern humans from Africa through the Near East

The recent African origin of modern humans or the "Out of Africa" theory (OOA)[a] holds that present-day humans outside Africa descend mainly from a single expansion of anatomically modern humans (Homo sapiens) from Africa about 70,000–50,000 years ago. It is the most widely accepted[1][2][3] paleo-anthropological model of the geographic origin and early migration of our species.

This expansion follows the early expansions of hominins out of Africa, accomplished by Homo erectus and then Homo neanderthalensis.

The model proposes a "single origin" of Homo sapiens in the taxonomic sense, precluding parallel evolution in other regions of traits considered anatomically modern,[4] but not precluding multiple admixture between H. sapiens and archaic humans in Europe and Asia.[b][5][6] H. sapiens most likely developed in the Horn of Africa between 300,000 and 200,000 years ago,[7][8] although an alternative hypothesis argues that diverse morphological features of H. sapiens appeared locally in different parts of Africa and converged due to gene flow between different populations within the same period.[9][10] The "recent African origin" model proposes that all modern non-African populations are substantially descended from populations of H. sapiens that left Africa after that time.

There were at least several "out-of-Africa" dispersals of modern humans, possibly beginning as early as 270,000 years ago, certainly via northern Africa and the Arabian Peninsula about 130,000 to 115,000 years ago at least.[17] There is evidence that modern humans had reached China around 80,000 years ago.[18][19] Practically all of these early waves seem to have gone extinct or retreated back, and present-day humans outside Africa descend mainly from a single expansion about 70,000–50,000 years ago,[20][21][22][7][8][23][24][excessive citations] via the so-called "Southern Route". These humans spread rapidly along the coast of Asia and reached Australia by around 65,000–50,000 years ago,[25][26][c] (though some researchers question the earlier Australian dates and place the arrival of humans there at 50,000 years ago at earliest,[27][28] while others have suggested that these first settlers of Australia may represent an older wave before the more significant out of Africa migration and thus not necessarily be ancestral to the region's later inhabitants[22]) while Europe was populated by an early offshoot which settled the Near East and Europe less than 55,000 years ago.[29][30][31]

In the 2010s, studies in population genetics uncovered evidence of interbreeding that occurred between H. sapiens and archaic humans in Eurasia, Oceania and Africa,[32][33][34] indicating that modern population groups, while mostly derived from early H. sapiens, are to a lesser extent also descended from regional variants of archaic humans.

Proposed waves

[edit]
Further information: Early expansions of hominins out of Africa and Skhul and Qafzeh hominins
Layer sequence at Ksar Akil in the Levantine corridor, and discovery of two fossils of Homo sapiens, dated to 40,800 to 39,200 years BP for "Egbert",[35] and 42,400–41,700 BP for "Ethelruda".[35]

"Recent African origin", or Out of Africa II, refers to the migration of anatomically modern humans (Homo sapiens) out of Africa after their emergence at c. 300,000 to 200,000 years ago, in contrast to "Out of Africa I", which refers to the migration of archaic humans from Africa to Eurasia from before 1.8 and up to 0.5 million years ago. Omo-Kibish I (Omo I) from southern Ethiopia is the oldest anatomically modern Homo sapiens skeleton currently known (around 233,000 years old).[36] There are even older Homo sapiens fossils from Jebel Irhoud in Morocco which exhibit a mixture of modern and archaic features at around 315,000 years old.[37]

Since the beginning of the 21st century, the picture of "recent single-origin" migrations has become significantly more complex, due to the discovery of modern-archaic admixture and the increasing evidence that the "recent out-of-Africa" migration took place in waves over a long time. As of 2010, there were two main accepted dispersal routes for the out-of-Africa migration of early anatomically modern humans, the "Northern Route" (via Nile Valley and Sinai) and the "Southern Route" via the Bab-el-Mandeb strait.[38]

  • Posth et al. (2017) suggest that early Homo sapiens, or "another species in Africa closely related to us", might have first migrated out of Africa around 270,000 years ago based on the closer affinity within Neanderthals' mitochondrial genomes to Homo sapiens than Denisovans.[39]
  • An interpration, with as of yet limited recognition, of a skull fragment coming from Apidima Cave in Greece dated at 210,000 years ago as a Homo sapiens specimen may also points to an early Homo sapiens migration.[40] Finds at Misliya cave, which include a partial jawbone with eight teeth, that may belong to a Homo sapiens specimen, have been dated to around 185,000 years ago. Layers dating from between 250,000 and 140,000 years ago in the same cave contained tools of the Levallois type which could put the date of the first migration even earlier if the tools can be associated with the modern human jawbone finds.[41][42][43]
  • An eastward dispersal from Northeast Africa to Arabia 150,000–130,000 years ago is based on the stone tools finds at Jebel Faya dated to 127,000 years ago (discovered in 2011), although fossil evidence in the area is significantly later at 85,000 years ago.[11][44] Possibly related to this wave are the finds from Zhirendong cave, Southern China, dated to more than 100,000 years ago.[45] Other evidence of modern human presence in China has been dated to 80,000 years ago.[19]
  • The most significant out of Africa dispersal took place around 50,000–70,000 years ago via the so-called Southern Route, either before[46] or after[30][31] the Toba event, which happened between 69,000 and 77,000 years ago.[46] This dispersal followed the southern coastline of Asia and reached Australia around 65,000–50,000 years ago or according to some research, by 50,000 years ago at earliest.[27][28] Western Asia was "re-occupied" by a different derivation from this wave around 50,000 years ago and Europe was populated from Western Asia beginning around 43,000 years ago.[38]
  • Wells (2003) describes an additional wave of migration after the southern coastal route, a northern migration into Europe about 45,000 years ago.[d] This possibility is ruled out by Macaulay et al. (2005) and Posth et al. (2016), who argue for a single coastal dispersal, with an early offshoot into Europe.

Northern Route dispersal

[edit]
Further information: Skhul and Qafzeh hominins
See also: Levantine corridor
Anatomically Modern Humans known archaeological remains in Europe and Africa, directly dated, calibrated carbon dates as of 2013.[35]

Beginning 135,000 years ago, tropical Africa experienced megadroughts which drove humans from the land and towards the sea shores, and forced them to cross over to other continents.[47][e]

Fossils of early Homo sapiens were found in Qafzeh and Es-Skhul Caves in Israel and have been dated to 80,000 to 120,000 years ago.[48][49] 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.[20] Hua Liu et al. analyzed autosomal microsatellite markers dating to about 56,000 years ago. They interpret the paleontological fossil as an isolated early offshoot that retracted back to Africa.[21]

The discovery of stone tools in the United Arab Emirates in 2011 at the Faya-1 site in Mleiha, Sharjah, indicated the presence of modern humans at least 125,000 years ago,[11] leading to a resurgence of the "long-neglected" North African route.[12][50][13][14] This new understanding of the role of the Arabian dispersal began to change following results from archaeological and genetic studies stressing the importance of southern Arabia as a corridor for human expansions out of Africa.[51]

In Oman, a site was discovered by Bien Joven in 2011 containing more than 100 surface scatters of stone tools belonging to the late Nubian Complex, known previously only from archaeological excavations in the Sudan. Two optically stimulated luminescence age estimates placed the Arabian Nubian Complex at approximately 106,000 years old. This provides evidence for a distinct Stone Age technocomplex in southern Arabia, around the earlier part of the Marine Isotope Stage 5.[52]

According to Kuhlwilm and his co-authors, Neanderthals contributed genetically to modern humans then living outside of Africa around 100,000 years ago: humans which had already split off from other modern humans around 200,000 years ago, and this early wave of modern humans outside Africa also contributed genetically to the Altai Neanderthals.[53] They found 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".[53] According to co-author Ilan Gronau, "This actually complements archaeological evidence of the presence of early modern humans out of Africa around and before 100,000 years ago by providing the first genetic evidence of such populations."[53] Similar genetic admixture events have been noted in other regions as well.[54]

Southern Route dispersal

[edit]
Main article: Southern Dispersal
Further information: List of first human settlements

Coastal route

[edit]
Red Sea crossing

By some 50–70,000 years ago, a subset 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, only a small group, possibly as few as 150 to 1,000 people, crossed the Red Sea.[55][56] The group that crossed the Red Sea travelled along the coastal route around Arabia and the Persian Plateau to India, which appears to have been the first major settling point.[57] Wells (2003) argued for the route along the southern coastline of Asia, across about 250 kilometres (155 mi), reaching Australia by around 50,000 years ago.

Migration routes of modern humans, showing the northern route populating Western Eurasia, and the southern/coastal route populating Eastern Eurasia.

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 channel was much narrower. Though the straits were never completely closed, they were narrow enough to have enabled crossing using simple rafts, and there may have been islands in between.[38][58] Shell middens 125,000 years old have been found in Eritrea,[59] indicating that the diet of early humans included seafood obtained by beachcombing.

Toba eruption

[edit]
Main article: Toba catastrophe theory

The dating of the Southern Dispersal is a matter of dispute.[46] 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 in Sumatra, Indonesia. Stone tools discovered below the layers of ash deposited in India may point to a pre-Toba dispersal but the source of the tools is disputed.[46] 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".[46] Some research showing slower than expected genetic mutations in human DNA was published in 2012, indicating a revised dating for the migration to between 90,000 and 130,000 years ago.[60] Some more recent research suggests a migration out-of-Africa of around 50,000-65,000 years ago of the ancestors of modern non-African populations, similar to most previous estimates.[22][61][62]

West Asia

[edit]

Following the fossils dating 80,000 to 120,000 years ago from Qafzeh and Es-Skhul Caves in Israel there are no H. sapiens fossils in the Levant until the Manot 1 fossil from Manot Cave in Israel, dated to 54,700 years ago,[63] though the dating was questioned by Groucutt et al. (2015). The lack of fossils and stone tool industries that can be safely associated with modern humans in the Levant has been taken to suggest that modern humans were outcompeted by Neanderthals until around 55,000 years ago, who would have placed a barrier on modern human dispersal out of Africa through the Northern Route.[64][failed verification] Climate reconstructions also support a Southern Route dispersal of modern humans as the Bab-el-Mandeb strait experienced a climate more conductive to human migration than the northern landbridge to the Levant during the major human dispersal out of Africa.[65]

A 2023 study proposed that Eurasians and Africans genetically diverged ~100,000 years ago. Main Eurasians then lived in the Saudi Peninsula, genetically isolated from at least 85 kya, before expanding north 54 kya. For reference, Homo sapiens and Neanderthals diverged ~500 kya.[66]

Oceania

[edit]

Fossils from Lake Mungo, Australia, have been dated to about 42,000 years ago.[67][68] Other fossils from a site called Madjedbebe have been dated to at least 65,000 years ago,[69][70] though some researchers doubt this early estimate and date the Madjedbebe fossils at about 50,000 years ago at the oldest.[27][28]

Phylogenetic data suggests that an early Eastern Eurasian (Eastern non-African) meta-population trifurcated somewhere in eastern South Asia, and gave rise to the Australo-Papuans, the Ancient Ancestral South Indians (AASI), as well as East/Southeast Asians, although Papuans may have also received some gene flow from an earlier group (xOoA), around 2%,[71] next to additional archaic admixture in the Sahul region.[72][73]

According to one study, Papuans could have either formed from a mixture between an East Eurasian lineage and lineage basal to West and East Asians, or as a sister lineage of East Asians with or without a minor basal OoA or xOoA contribution.[74]

A Holocene hunter-gatherer sample (Leang_Panninge) from South Sulawesi was found to be genetically in between East-Eurasians and Australo-Papuans. The sample could be modeled as ~50% Papuan-related and ~50% Basal-East Asian-related (Andamanese Onge or Tianyuan). The authors concluded that Basal-East Asian ancestry was far more widespread and the peopling of Insular Southeast Asia and Oceania was more complex than previously anticipated.[75][76]

East and Southeast Asia

[edit]

In China, the Liujiang man (Chinese: 柳江人) is among the earliest modern humans found in East Asia.[77] The date most commonly attributed to the remains is 67,000 years ago.[78] High rates of variability yielded by various dating techniques carried out by different researchers place the most widely accepted range of dates with 67,000 BP as a minimum, but do not rule out dates as old as 159,000 BP.[78] Liu, Martinón-Torres et al. (2015) claim that modern human teeth have been found in China dating to at least 80,000 years ago.[79]

Tianyuan man from China has a probable date range between 38,000 and 42,000 years ago, while Liujiang man from the same region has a probable date range between 67,000 and 159,000 years ago. According to 2013 DNA tests, Tianyuan man is related "to many present-day Asians and Native Americans".[80][81][82][83][84] Tianyuan is similar in morphology to Liujiang man, and some Jōmon period modern humans found in Japan, as well as modern East and Southeast Asians.[85][86][87]

A 2021 study about the population history of Eastern Eurasia, concluded that distinctive Basal-East Asian (East-Eurasian) ancestry originated in Mainland Southeast Asia at ~50,000BC from a distinct southern Himalayan route, and expanded through multiple migration waves southwards and northwards respectively.[88]

According to a 2024 study, Southeast Asia was the "demographic center of expansion" after some Out of African migrants returned to Africa, evident by the presence of basal Y-chromosome Eurasian lineages (C, D, F, K) in the region.[89]

Americas

[edit]

Genetic studies concluded that Native Americans descended from a single founding population that initially split from a Basal-East Asian source population in Mainland Southeast Asia around 36,000 years ago, at the same time at which the proper Jōmon people split from Basal-East Asians, either together with Ancestral Native Americans or during a separate expansion wave. They also show that the basal northern and southern Native American branches, to which all other Indigenous peoples belong, diverged around 16,000 years ago.[90][91] An indigenous American sample from 16,000BC in Idaho, which is craniometrically similar to modern Native Americans as well as Paleosiberians, was found to have largely East-Eurasian ancestry and showed high affinity with contemporary East Asians, as well as Jōmon period samples of Japan, confirming that Ancestral Native Americans split from an East-Eurasian source population in Eastern Siberia.[92]

Europe

[edit]

According to Macaulay et al. (2005), an early offshoot from the southern dispersal with haplogroup N followed the Nile from East Africa, heading northwards and crossing into Asia through the Sinai. This group then branched, some moving into Europe and others heading east into Asia.[30] This hypothesis is supported by the relatively late date of the arrival of modern humans in Europe as well as by archaeological and DNA evidence.[30] Based on an analysis of 55 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". By 45,000 years ago, modern humans are known to have reached northwestern Europe.[93]

Genetic reconstruction

[edit]

Mitochondrial haplogroups

[edit]

Within Africa

[edit]
Further information: Genetic history of Africa
See also: Most recent common ancestor, Archaeogenetics, and Human mitochondrial DNA haplogroup
Map of early diversification of modern humans according to mitochondrial population genetics (see: Haplogroup L).

The first lineage to branch off from Mitochondrial Eve was L0. This haplogroup is found in high proportions among the San of Southern Africa and the Sandawe of East Africa. It is also found among the Mbuti people.[94][95] These groups branched off early in human history and have remained relatively genetically isolated since then. Haplogroups L1, L2, and L3 are descendants of L1–L6, and are largely confined to Africa. The macro haplogroups M and N, which are the lineages of the rest of the world outside Africa, descend from L3. L3 is about 70,000 years old, while haplogroups M and N are about 65–55,000 years old.[96][62] The relationship between such gene trees and demographic history is still debated when applied to dispersals.[97]

Of all the lineages present in Africa, the female descendants of only 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. 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 North-east Africa) and appear to be more recent arrivals.[citation needed] A possible explanation is that these mutations occurred in East Africa shortly before the exodus and became the dominant haplogroups thereafter by means of the founder effect. Alternatively, the mutations may have arisen shortly afterwards.

Southern Route and haplogroups M and N

[edit]

Results from mtDNA collected from aboriginal Malaysians called Orang Asli indicate that the haplogroups M and N share characteristics with original African groups from approximately 85,000 years ago, and share characteristics with sub-haplogroups found in coastal south-east Asian regions, such as Australasia, the Indian subcontinent and throughout continental Asia, which had dispersed and separated from their African progenitor approximately 65,000 years ago. This southern coastal dispersal would have occurred before the dispersal through the Levant approximately 45,000 years ago.[30] 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 thought to have been destroyed by the rise in sea levels during the Holocene epoch.[98] Alternatively, a small European founder population that had expressed haplogroup M and N at first, 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 Arabia and Persia until reaching India.[57] 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.[57] Sixty percent 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 the mainland. They are evidence of the coastal route of early settlers that extends from India to Thailand and Indonesia all the way to eastern New Guinea. Since M is found in high frequencies in highlanders from New Guinea and the Andamanese and New Guineans have dark skin and Afro-textured hair, some scientists think they are all part of the same wave of migrants who departed across the Red Sea ~60,000 years ago in the Great Coastal Migration. The proportion of haplogroup M increases eastwards from Arabia to India; in eastern India, M outnumbers N by a ratio of 3:1. Crossing into Southeast Asia, haplogroup N (mostly in the form of derivatives of its R subclade) reappears as the predominant lineage.[citation needed] M is predominant in East Asia, but amongst Indigenous Australians, N is the more common lineage.[citation needed] This haphazard distribution of Haplogroup N from Europe to Australia can be explained by founder effects and population bottlenecks.[99]

Autosomal DNA

[edit]
Further information: Human genetic variation
The earliest-branching non-African paternal lineages (C, D, F) after the out-of-Africa event (a), and their deepest divergence among modern day East or Southeast Asia (b), suggesting rapid coastal expansions. Simplified Y-chromosome tree is shown as reference for colours.[100]

A 2002 study of African, European, and Asian populations found greater genetic diversity among Africans than among Eurasians, and that genetic diversity among Eurasians is largely a subset of that among Africans, supporting the out-of-Africa model.[101] A large study by Coop et al. (2009) found evidence for natural selection in autosomal DNA outside of Africa. The study distinguishes non-African sweeps (notably KITLG variants associated with skin color), West-Eurasian sweeps (SLC24A5) and East-Asian sweeps (MC1R, relevant to skin color). Based on this evidence, the study concluded that human populations encountered novel selective pressures as they expanded out of Africa.[102] MC1R and its relation to skin color had already been discussed by Harding et al. (2000), p. 1355. According to this study, Papua New Guineans continued to be exposed to selection for dark skin color so that, although these groups are distinct from Africans in other places, the allele for dark skin color shared by contemporary Africans, Andamanese and New Guineans is an archaism. Endicott et al. (2003) suggest convergent evolution. A 2014 study by Gurdasani et al. indicates that the higher genetic diversity in Africa was further increased in some regions by relatively recent Eurasian migrations affecting parts of Africa.[103]

Pathogen DNA

[edit]

Another promising route towards reconstructing human genetic genealogy is via the JC virus (JCV), a type of human polyomavirus which is carried by 70–90 percent of humans and which is usually transmitted vertically, from parents to offspring, suggesting codivergence with human populations. For this reason, JCV has been used as a genetic marker for human evolution and migration.[104] This method does not appear to be reliable for the migration out of Africa; in contrast to human genetics, JCV strains associated with African populations are not basal. From this Shackelton et al. (2006) conclude that either a basal African strain of JCV has become extinct or that the original infection with JCV post-dates the migration from Africa.

Admixture of archaic and modern humans

[edit]
Main article: Interbreeding between archaic and modern humans

Evidence for archaic human species (descended from Homo heidelbergensis) having interbred with modern humans outside of Africa, was discovered in the 2010s. This concerns primarily Neanderthal admixture in all modern populations except for Sub-Saharan Africans but evidence has also been presented for Denisova hominin admixture in Australasia (i.e. in Melanesians, Aboriginal Australians and some Negritos).[105] The rate of Neanderthal admixture to European and Asian populations as of 2017 has been estimated at between about 2–3%.[106]

Archaic admixture in some Sub-Saharan African populations hunter-gatherer groups (Biaka Pygmies and San), derived from archaic hominins that broke away from the modern human lineage around 700,000 years ago, was discovered in 2011. The rate of admixture was estimated at 2%.[34] Admixture from archaic hominins of still earlier divergence times, estimated at 1.2 to 1.3 million years ago, was found in Pygmies, Hadza and five Sandawe in 2012.[107][33]

From an analysis of Mucin 7, a highly divergent haplotype that has an estimated coalescence time with other variants around 4.5 million years BP and is specific to African populations, it is inferred to have been derived from interbreeding between African modern and archaic humans.[108]

A study published in 2020 found that the Yoruba and Mende populations of West Africa derive between 2% and 19% of their genome from an as-yet unidentified archaic hominin population that likely diverged before the split of modern humans and the ancestors of Neanderthals and Denisovans.[109]

Stone tools

[edit]
Further information: Aterian, Baradostian, and Microlith

In addition to genetic analysis, Petraglia et al. also examines the small stone tools (microlithic materials) from the Indian subcontinent and explains the expansion of population based on the reconstruction of paleoenvironment. He proposed that the stone tools could be dated to 35 ka in South Asia, and the new technology might be influenced by environmental change and population pressure.[110]

History of the theory

[edit]

Classical paleoanthropology

[edit]
Further information: Timeline of human evolution and Paleoanthropology § History of paleoanthropology
The frontispiece to Huxley's Evidence as to Man's Place in Nature (1863): the image compares the skeleton of a human to other apes.
The possibility of an origin of L3 in Asia was proposed by Cabrera et al. (2018).[111]
a: Exit of the L3 precursor to Eurasia. b: Return to Africa and expansion to Asia of basal L3 lineages with subsequent differentiation in both continents.

The cladistic relationship of humans with the African apes was suggested by Charles Darwin after studying the behaviour of African apes, one of which was displayed at the London Zoo.[112] The anatomist Thomas Huxley had also supported the hypothesis and suggested that African apes have a close evolutionary relationship with humans.[113] These views were 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 South-east Asia and rejected Darwin's African hypothesis.[114][115]

In The Descent of Man, Darwin speculated that humans had descended from apes, which still had small brains but walked upright, freeing their hands for uses which favoured intelligence; he thought such apes were African:

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. But it is useless to speculate on this subject, for an ape nearly as large as a man, namely the Dryopithecus of Lartet, which was closely allied to the anthropomorphous Hylobates, existed in Europe during the Upper Miocene period; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale.

— Charles Darwin, Descent of Man[116]

In 1871, there were hardly any human fossils of ancient hominins available. Almost fifty years later, Darwin's speculation was supported when anthropologists began finding fossils of ancient small-brained hominins in several areas of Africa (list of hominina fossils). The hypothesis of recent (as opposed to archaic) African origin developed in the 20th century. The "recent African origin" of modern humans means "single origin" (monogenism) and has been used in various contexts as an antonym to polygenism. The debate in anthropology had swung in favour of monogenism by the mid-20th century. Isolated proponents of polygenism held forth in the mid-20th century, such as Carleton Coon, who thought as late as 1962 that H. sapiens arose five times from H. erectus in five places.[117]

Multiregional origin hypothesis

[edit]
Main article: Multiregional origin of modern humans

The historical alternative to the recent origin model is the multiregional origin of modern humans, initially proposed by Milford Wolpoff in the 1980s. This view proposes that the derivation of anatomically modern human populations from H. erectus at the beginning of the Pleistocene 1.8 million years BP, has taken place within a continuous world population. The hypothesis necessarily rejects the assumption of an infertility barrier between ancient Eurasian and African populations of Homo. The hypothesis was controversially debated during the late 1980s and the 1990s.[118] The now-current terminology of "recent-origin" and "Out of Africa" became current in the context of this debate in the 1990s.[119] Originally seen as an antithetical alternative to the recent origin model, the multiregional hypothesis in its original "strong" form is obsolete, while its various modified weaker variants have become variants of a view of "recent origin" combined with archaic admixture.[120] Stringer (2014) distinguishes the original or "classic" Multiregional model as having existed from 1984 (its formulation) until 2003, to a "weak" post-2003 variant that has "shifted close to that of the Assimilation Model".[121][122]

Mitochondrial analyses

[edit]
Further information: Mitochondrial Eve

In the 1980s, Allan Wilson together with Rebecca L. Cann and Mark Stoneking worked on genetic dating of the matrilineal most recent common ancestor of modern human populations (dubbed "Mitochondrial Eve"). To identify informative genetic markers for tracking human evolutionary history, Wilson concentrated on mitochondrial DNA (mtDNA), which is maternally inherited. This DNA material mutates quickly, making it easy to plot changes over relatively short times. With his discovery that human mtDNA is genetically much less diverse than chimpanzee mtDNA, Wilson concluded that modern human populations had diverged recently from a single population while older human species such as Neanderthals and Homo erectus had become extinct.[123] With the advent of archaeogenetics in the 1990s, the dating of mitochondrial and Y-chromosomal haplogroups became possible with some confidence. By 1999, estimates ranged around 150,000 years for the mt-MRCA and 60,000 to 70,000 years for the migration out of Africa.[124]

From 2000 to 2003, there was controversy about the mitochondrial DNA of "Mungo Man 3" (LM3) and its possible bearing on the multiregional hypothesis. LM3 was found to have more than the expected number of sequence differences when compared to modern human DNA (CRS).[125] Comparison of the mitochondrial DNA with that of ancient and modern aborigines, led to the conclusion that Mungo Man fell outside the range of genetic variation seen in Aboriginal Australians and was used to support the multiregional origin hypothesis. A reanalysis of LM3 and other ancient specimens from the area published in 2016, showed it to be akin to modern Aboriginal Australian sequences, inconsistent with the results of the earlier study.[126]

Y-chromosome analyses

[edit]
Further information: Y-chromosomal Adam
Map of Y-chromosome haplogroups – dominant haplogroups in pre-colonial populations with proposed migrations routes

The Y chromosome, which is paternally inherited, does not go through much recombination and thus stays largely the same after inheritance. Similar to Mitochondrial Eve, this could be studied to track the male most recent common ancestor ("Y-chromosomal Adam" or Y-MRCA).[127]

The most basal lineages have been detected in West, Northwest and Central Africa, suggesting plausibility for the Y-MRCA living in the general region of "Central-Northwest Africa".[13]

A Stanford University School of Medicine study was done by comparing Y-chromosome sequences and mtDNA in 69 men from different geographic regions and constructing a family tree. It was found that the Y-MRCA lived between 120,000 and 156,000, and the Mitochondrial Eve lived between 99,000 and 148,000 years ago, which not only predates some proposed waves of migration, but also meant that both lived in the African continent around the same time.[128]

Another study finds a plausible placement in "the north-western quadrant of the African continent" for the emergence of the A1b haplogroup.[129] The 2013 report of haplogroup A00 found among the Mbo people of western present-day Cameroon is also compatible with this picture.[130]

The revision of Y-chromosomal phylogeny since 2011 has affected estimates for the likely geographical origin of Y-MRCA as well as estimates on time depth. By the same reasoning, future discovery of presently-unknown archaic haplogroups in living people would again lead to such revisions. In particular, the possible presence of between 1% and 4% Neanderthal-derived DNA in Eurasian genomes implies that the (unlikely) event of a discovery of a single living Eurasian male exhibiting a Neanderthal patrilineal line would immediately push back T-MRCA ("time to MRCA") to at least twice its current estimate. However, the discovery of a Neanderthal Y-chromosome by Mendez et al. was tempered by a 2016 study that suggests the extinction of Neanderthal patrilineages, as the lineage inferred from the Neanderthal sequence is outside of the range of contemporary human genetic variation.[131] Questions of geographical origin would become part of the debate on Neanderthal evolution from Homo erectus.

See also

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Notes

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Further reading

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Recent African origin of modern humans

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The Recent African origin of modern humans, also known as the model, posits that anatomically modern Homo sapiens first evolved across approximately 300,000 years ago through a pan-African process involving multiple populations and regions, before a primary dispersal event around 60,000–70,000 years ago led to the colonization of , Australia, and the Americas by a subset of these African groups, who largely replaced or assimilated archaic hominins like Neanderthals in Europe and West Asia and Denisovans in Asia with only limited . Fossil evidence forms the cornerstone of this model, with the earliest known H. sapiens remains discovered at in , dated to 315,000 ± 34,000 years ago via on associated stone tools and sediments; these fossils exhibit a mosaic of modern facial features and more archaic braincase morphology, supporting an African origin predating previous estimates by over 100,000 years. Additional key sites include the Omo Kibish remains in (~233,000 years old, confirmed by recent uranium-series dating) and the Herto skulls in (~160,000 years old), which display fully modern traits and underscore the deep temporal and geographic breadth of H. sapiens evolution within during the . These findings refute earlier single-origin hypotheses focused on , instead indicating a continent-wide evolutionary process shaped by environmental variability and . Genetic data provide compelling support, revealing the highest levels of diversity in African populations compared to non-Africans, consistent with an African origin and subsequent bottlenecks during dispersal; for instance, and Y-chromosome phylogenies trace all modern human lineages to African ancestors diverging around 200,000–300,000 years ago. Whole-genome analyses further demonstrate that non-African genomes derive primarily from a single major out-of- migration event circa 50,000–70,000 years ago, with effective sizes in remaining larger and more structured, reflecting long-term continuity rather than recent replacement within the continent. While archaic admixture contributes 1–4% DNA to non-Africans and variable "ghost" archaic ancestry to some African groups, the overwhelming shared ancestry among all modern humans points to a unified recent African source, distinguishing this model from multiregional alternatives. The dispersal phase involved multiple waves, with archaeological and genetic traces of earlier, unsuccessful forays into the Levant and Arabia as far back as 120,000–180,000 years ago, but the successful expansion that founded non-African populations occurred amid favorable climatic windows around 70,000–50,000 years ago, enabling adaptation to diverse Eurasian environments through technological innovations like advanced stone tools and symbolic behavior. This migration route likely followed the southern coastal pathway across the Arabian Peninsula, leading to rapid population growth and niche expansion by 50,000 years ago, as evidenced by increased archaeological density and genetic signals of serial founder effects in descendant populations. Overall, the model integrates multidisciplinary evidence to explain the unity of modern humanity while highlighting Africa's role as the cradle of our species' behavioral and biological modernity.

Core Model and Principles

Definition and Key Tenets

The Recent African Origin (RAO) model, also known as the hypothesis, posits that anatomically modern Homo sapiens originated in between approximately 300,000 and 200,000 years ago and subsequently dispersed to other continents, replacing archaic human populations outside with minimal interbreeding. This framework emphasizes 's role as the cradle of modern humanity, supported by both fossil and genetic evidence indicating that all contemporary human populations trace their ancestry to this African source. Central tenets of the RAO include a single continental origin for modern humans in , where is highest due to serial founder effects during migrations that progressively reduced variation in descendant populations outside the continent. —encompassing advanced symbolic thinking, complex tool use, and cultural innovations—also emerged in prior to these dispersals, setting the stage for global expansion. Recent studies (as of 2024–2025) highlight complex across , including structured metapopulations and back-migrations, reinforcing the pan-African nature of this evolution. These patterns of , with harboring the greatest allelic richness and , underscore the model's prediction of a recent, localized evolutionary event rather than widespread parallel development. The designation "recent" in RAO distinguishes this event from earlier dispersals of archaic Homo species, such as H. erectus, which occurred over a million years ago and involved different hominin lineages. In contrast to assimilation or multiregional models that suggest substantial genetic continuity and interbreeding with archaic humans across regions, RAO advocates a near-total replacement scenario, where modern humans supplanted existing populations with only limited .

Timeline of Emergence and Expansion

The earliest undisputed fossils attributed to Homo sapiens come from in , dated to approximately 315,000 years ago through of associated artifacts and sediments. These remains, including a partial and , exhibit a mix of modern and archaic features, such as a globular braincase alongside a more elongated cranium, supporting a pan-African origin for the species during the Middle Pleistocene. A 2025 study of a ~1-million-year-old from Yunxian, , suggests potential earlier divergence in the H. sapiens lineage, possibly pushing origins back significantly, though this remains under debate and does not alter the African emergence of anatomically modern forms. In eastern , the Omo Kibish site in yields fossils dated to around 233,000 years ago via argon-argon dating of overlying volcanic ash layers, providing evidence of morphology in the region and indicating behavioral indicators of modernity, such as advanced tool use. The initial diversification of Homo sapiens in spanned roughly 300,000 to 100,000 years ago, marked by regional morphological variations and population expansions across diverse environments from to southern savannas. During this period, back-migrations within the continent—such as movements from eastern to western and vice versa—contributed to genetic structuring and adaptation, as inferred from archaeological distributions of technologies. Pre-dispersal adaptations, including the emergence of symbolic behavior, are exemplified by engraved pieces from in , dated to approximately 75,000–100,000 years ago through optically stimulated , which demonstrate intentional patterning and abstract thinking. Key drivers of this expansion included climatic fluctuations, particularly the wet periods of (approximately 130,000 to 71,000 years ago), which increased rainfall across the and regions, facilitating and connectivity between sub-Saharan and North African groups. Technological innovations, such as the for producing standardized stone flakes, originated in during the and enhanced hunting efficiency and resource exploitation, as seen in assemblages from sites like the Kapthurin Formation in dating back over 200,000 years. Recent analyses (as of 2025) indicate substantial niche expansion in from around 70,000 years ago, driven by diverse habitat use, preceding major out-of-Africa dispersals. Genetic modeling of African populations estimates the of Homo sapiens during this era at approximately 10,000 to 15,000 individuals, reflecting a structured that maintained high amid environmental pressures. This demographic stability underpinned the species' resilience and set the foundation for later global dispersals, aligning with the core tenets of the Recent African Origin model.

Migration Waves and Routes

Southern Route Dispersal

The Southern Route Dispersal represents the primary pathway for the early exodus of anatomically modern humans (Homo sapiens) from , occurring between approximately 70,000 and 50,000 years ago via the strait at the southern end of the . Earlier dispersals via this route, between 100,000 and 200,000 years ago, were largely unsuccessful and did not lead to sustained populations outside Africa. During Marine Isotope Stage 4, lowered sea levels—reducing the strait to a width of about 10-20 kilometers—enabled crossings on foot across exposed shoals or via rudimentary watercraft, allowing small groups to enter the from the . This route capitalized on coastal refugia, where monsoon-enhanced environments provided reliable marine and riparian resources, supporting sustained migration along the rim. Key events in this dispersal include the initial settlement of southern Arabia approximately 80,000 years ago, with evidence of earlier occupations dating back to around 125,000 years ago, as evidenced by lithic artifacts at in the , which exhibit technological affinities to African industries. These earlier occupations appear to have been transient and failed to establish lasting populations. From there, the migration progressed rapidly eastward, reaching the Indian subcontinent by at least 74,000 years ago, demonstrated by stratified stone tools at Jwalapuram in southern that align with behaviors such as Levallois flaking. These early arrivals adapted to tropical environments by exploiting diverse habitats, including monsoon forests and coastal zones, which offered , fish, and terrestrial game, fostering behavioral flexibility in resource use. The dispersal continued southeastward, leading to the peopling of Australia around 65,000 to 50,000 years ago, with archaeological evidence from sites such as Madjedbebe rock shelter in northern Australia, where stone artifacts and ochre dated via optically stimulated luminescence confirm early human occupation. The dispersal encompassed both coastal and inland sub-routes, with the coastal path serving as the dominant corridor due to its resource predictability, though inland valleys and oases facilitated detours in arid interiors like the Arabian interior. This Southern Dispersal wave is genetically marked as the main conduit for derivatives of mitochondrial , including non-African clades M and N, which arose shortly after and underpin the mtDNA diversity of and beyond. A significant environmental challenge was the Toba supereruption on approximately 74,000 years ago, which triggered a and has been hypothesized to impose a severe on early dispersers. However, continuous occupation layers at Jwalapuram, spanning the eruption, provide direct evidence of human resilience and survival in refugial settings, countering notions of near-extinction and highlighting adaptive strategies like shelter use and dietary diversification.

Northern Route Dispersal

The Northern Route dispersal involved anatomically modern humans exiting via the and entering the , marking a key pathway for subsequent expansions into , , and ultimately the . This route, distinct from earlier coastal migrations, is associated with a major successful wave approximately 50,000 to 40,000 years ago, during which small groups traversed arid and semi-arid landscapes facilitated by intermittent wetter conditions in the region. Archaeological and genetic evidence indicates that these migrants carried advanced tool technologies, enabling adaptation to diverse Eurasian environments. Key phases of this dispersal include initial, unsuccessful forays as early as 180,000 years ago, including the Misliya jawbone dated to 177,000–194,000 years ago, followed by the Skhul and Qafzeh fossils from , dated to approximately 120,000–90,000 years ago during Marine Isotope Stage (MIS) 5. These early modern humans briefly occupied Levantine sites but did not establish lasting populations beyond the region, likely due to climatic reversals and competition. A successful expansion followed during MIS 3 (approximately 60,000–30,000 years ago), an interstadial period of relative climatic mildness that supported human movement northward. This phase saw dispersals into and Europe, including the arrival of culture bearers in Europe around 45,000 years ago, who introduced blade-based technologies and symbolic artifacts. Later, descendants of these northern dispersers crossed the Bering land bridge into the approximately 23,000 to 15,000 years ago, populating the during the . Environmental factors played a crucial role, with overlaps in ranges in the and influencing interactions, including limited admixture events. Glacial cycles during MIS 3 created steppe-tundra corridors across , providing accessible pathways for hunter-gatherers despite cold conditions, while periodic wetting in the Sinai-Levant corridor supported refugia like paleolakes. These dynamics favored mobile groups adapted to open landscapes. Population dynamics along the Northern Route featured smaller founder groups, leading to genetic bottlenecks that reduced diversity in non-African lineages. Estimates suggest effective population sizes of 1,000 to 2,500 individuals during the primary out-of-Africa expansion around 60,000–45,000 years ago, reflecting serial founder effects as groups splintered into . This bottleneck magnitude, a 5- to 10-fold reduction from ancestral African sizes of 12,800–14,400, underscores the challenges of long-distance migration through variable terrains.

Genetic Evidence

Mitochondrial and Y-Chromosome Haplogroups

(mtDNA) is inherited solely from the mother and serves as a powerful uniparental marker for tracing maternal lineages in . The deepest branches of the human mtDNA phylogeny, encompassing macrohaplogroups L0 through L6, originated in approximately 150,000 to 200,000 years ago, reflecting the emergence of modern human maternal diversity on the continent. Phylogenetic analyses of complete mtDNA genomes from diverse African populations confirm that L0 represents the most basal lineage, with its (TMRCA) estimated at around 152,000 to 170,000 years ago, followed by subsequent diversification into L1, L2, L5, and L6 within . These haplogroups exhibit the highest levels of in African populations, particularly among and Pygmy groups, underscoring 's role as the cradle of modern human mtDNA variation. A key event in the mtDNA phylogeny is the emergence of , whose TMRCA is dated to approximately 70,000 years ago in eastern or northeastern , based on coalescent time calculations from phylogenetic trees of full mtDNA sequences. L3 served as the ancestral lineage for the non-African macrohaplogroups and , which arose shortly thereafter through rapid diversification and are now predominant outside ; for instance, the TMRCA of M is estimated at 61,000 to 66,000 years ago, and N at around 68,000 years ago. These estimates derive from Bayesian phylogenetic methods calibrated with mutation rates from and complete genome sequencing, supporting a single major dispersal event from carrying these lineages. The study of mtDNA haplogroups relies on sequencing techniques targeting the hypervariable regions (HVR-I and HVR-II) of the control region, as well as full mitochondrial genomes, which have become standard since the early with advances in next-generation sequencing. rates in mtDNA are estimated at approximately one substitution per 3,000 to 5,000 years across the entire ~16.5 kb genome, with higher rates in the control region (~1 per 1,000 to 2,000 years) used to calibrate phylogenetic clocks; these rates are derived from pedigree studies and comparisons. Such methods enable precise reconstruction of times and migration patterns, revealing a serial where mtDNA diversity decreases with geographic distance from , as variance in allele frequencies declines proportionally to 1/distance from . Y-chromosome DNA, passed exclusively from father to son, complements mtDNA by tracing paternal lineages and similarly supports an African origin for modern humans. The most basal Y-chromosome haplogroups, A and B (including sub-clades like A1b found in Pygmies and ), are nearly exclusive to African populations and represent the root of the human Y phylogeny, with their TMRCA estimated at over 100,000 years ago. These lineages exhibit high diversity within , consistent with long-term residence and expansion on the continent. Non-African Y-chromosome diversity stems primarily from the CT (or DE* + ) macrohaplogroup, whose TMRCA is approximately 60,000 to 70,000 years ago, marking the major out-of- paternal bottleneck and dispersal. From CT, haplogroups C, D, E, and F emerged, showing star-like phylogenetic expansions indicative of rapid post-dispersal; for example, F-M89, ancestral to most Eurasians, displays a burst of diversity around 50,000 years ago. These patterns are inferred from high-resolution sequencing of the non-recombining portion of the , using single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs) to build global phylogenies. Y-chromosome diversity also follows a serial founder model, with the lowest variation outside and a gradient increasing toward the continent, paralleling mtDNA observations. Autosomal DNA studies provide broader confirmation of these uniparental signals but reveal additional complexity in biparental inheritance.

Autosomal DNA and Population Genetics

Autosomal DNA studies, which analyze the entire nuclear inherited from both parents, provide a comprehensive view of structure and , complementing uniparental markers like and Y-chromosomes. These analyses reveal high within African populations, reflecting their role as the cradle of modern humanity, while non-African populations exhibit reduced diversity due to founder effects during migrations. Whole-genome sequencing has enabled the reconstruction of effective sizes, admixture events, and divergence times, supporting the recent African origin model through patterns of sharing and . Recent 2024–2025 genomic surveys of diverse African ethnic groups, building on the , reaffirm that African populations harbor the greatest diversity, with non-Africans showing reduced variation due to serial founder effects. Key findings from ancient DNA highlight the deep branching of African lineages. For instance, genomes from the Ballito Bay site in , dating to approximately 2,000 years ago, represent some of the earliest sampled modern human remains and show the deepest divergences among African populations, with splits estimated at over 200,000 years ago between southern African foragers and other groups like the Dinka. This underscores the long-term continuity and basal position of African genetic diversity relative to non-Africans. Non-African populations, in contrast, trace their ancestry to a single out-of-Africa dispersal event involving a severe around 50,000–70,000 years ago, during which a small founding group carried a subset of African outward. This pattern of reduced genetic diversity outside Africa, with non-African variation forming a subset of African diversity and evidence of a bottleneck estimated at around 1,500 effective individuals post-migration, is inconsistent with the multiregional hypothesis, which requires continuous gene flow and parallel evolution across multiple regions to maintain higher diversity levels globally. Instead, it strongly supports the recent African origin model by demonstrating a single major dispersal from Africa following an African bottleneck. Common analytical methods in these studies include (PCA), which visualizes by projecting individuals onto axes of principal components, consistently showing African populations clustering at the periphery with the greatest spread, while non-Africans form a tighter central cluster derived from African diversity. ADMIXTURE software is widely used to estimate ancestry proportions by modeling genomes as mixtures of hypothetical ancestral populations, revealing fine-scale structure such as distinct West, East, and Southern African components. Demographic histories are inferred using the pairwise sequentially Markovian coalescent (PSMC) method, which reconstructs changes in (Ne) over time from individual genome sequences; post-bottleneck Ne for non-Africans is estimated at around 1,500, indicating a drastic reduction from pre-migration African levels of several thousand. Recent whole-genome studies from the 2020s, building on resources like the , confirm that over 90% of genetic ancestry in all modern human populations originates from African sources, with the remaining variation attributable to post-dispersal dynamics. These analyses also pinpoint the divergence between East Asian and West Eurasian ancestries to approximately 40,000 years ago, following the out-of-Africa exit, as evidenced by shared drift patterns and differences. Updates to large-scale datasets, including high-coverage sequencing of diverse African groups, have refined these estimates by incorporating more indigenous samples, reducing biases from Eurocentric reference panels. Demographic inferences from autosomal data further reveal back-migrations from into , introducing non-African alleles into various populations. For example, ancient genome analysis from shows that modern individuals carry 4–7% Eurasian-derived ancestry in many sub-Saharan African populations (e.g., Yoruba and Mbuti Pygmies), and substantially higher (40–50%) in Northeast African groups such as , from these events dated to around 3,000 years ago and linked to Neolithic farmer-related sources, which has shaped the genetic makeup of Northeast African groups without altering their predominantly African heritage. Such highlights ongoing connectivity between continents, with admixture proportions varying by region and ethnic group.

Archaic Human Admixture

Genomic analyses have revealed that non-African modern human populations carry approximately 1–4% ancestry, resulting from interbreeding events that occurred roughly 50,000–60,000 years ago in following the out-of-Africa dispersal. This admixture was initially detected through comparisons of the to modern human sequences, showing shared derived alleles absent in sub-Saharan Africans. Subsequent refinements used the decay of (LD) around introgressed segments to date the events and the S* statistic to identify archaic haplotypes without a reference archaic . Denisovan admixture into modern humans is evident in varying proportions across populations, with up to 5% ancestry in Oceanians such as Papuans and 0.1–0.5% in East Asians, arising from multiple independent interbreeding pulses. This was identified by sequencing high-coverage genomes from and comparing them to modern human data, revealing distinct Denisovan haplotypes that diverged from s. Evidence for multiple admixture events comes from the patchwork distribution of Denisovan segments, with some lineages predating the Neanderthal-Denisovan split and others post-dating it, as seen in comparisons to the Altai Neanderthal genome. In contrast to Eurasian archaic contributions, recent genomic studies from the 2020s have uncovered "" archaic in African populations, particularly West Africans, where estimates of approximately 2–8% in West African populations such as the Yoruba (~7%) and Esan (~2%), though earlier models included confidence intervals extending to 19%, derive from an unknown Homo that diverged prior to the Neanderthal-modern split. This admixture is estimated to have occurred around 43,000 years ago, detected using the S* statistic on high-coverage African genomes like those from the Yoruba, Esan, Mende, and Gambian populations, which show elevated LD decay indicative of archaic segments. The archaic source remains unidentified, as no fossils match the inferred divergence time of over 500,000 years ago, but the signal persists after accounting for modern structure. Archaic introgression has left functional legacies in modern humans, with some Neanderthal-derived alleles providing adaptive benefits, such as variants in immune-related genes like HLA that enhance resistance. These beneficial alleles have been positively selected and retained at higher frequencies, particularly in Eurasian populations exposed to new environments. Conversely, many deleterious archaic variants, including those linked to risk, have been purged through purifying selection over time, reducing their prevalence in contemporary genomes. There is no evidence of significant backflow of Eurasian archaic ancestry into African populations, as Neanderthal and signals in Africans are minimal and attributable to recent rather than direct interbreeding.

Archaeological and Fossil Evidence

African Fossil Record

The African fossil record provides critical evidence for the emergence and early diversification of anatomically modern Homo sapiens, with key specimens dating back over 300,000 years and displaying a mosaic of derived traits that distinguish them from contemporaneous archaic hominins. These fossils, from various regions across , including North, East, and South, illustrate a gradual morphological and behavioral transition rather than abrupt change, supporting the recent African origin model through continuity from Middle Pleistocene ancestors. The earliest known remains are from in , dated to approximately 315,000 ± 34,000 years ago, featuring modern facial features combined with a more archaic braincase, indicative of early stages in H. sapiens evolution. In Ethiopia's Herto region, three well-preserved crania (Homo sapiens idaltu) dated to approximately 160,000–154,000 years ago represent some of the earliest unambiguous examples of modern human morphology, featuring a high forehead, rounded occipital region, and reduced brow ridges. These traits mark a departure from the more robust features of earlier Homo species, with the Herto individuals classified as a bridging archaic and fully modern forms. Further south, at Border Cave in , , a partial adult cranium (BC 1) and other remains from layers, dated to approximately 170,000–82,000 years ago, exhibit modern-like features such as a gracile face and dental arcade, suggesting behavioral and anatomical modernity in southern African populations by this period. Meanwhile, the system in yielded over 1,500 fossils of , dated to 335,000–236,000 years ago, which, despite small and primitive limb proportions, coexisted with early Homo sapiens and provides archaic context for the in the region, though not a direct ancestor. Early Homo sapiens fossils in are characterized by distinctive cranial morphology, including high foreheads, globular braincases, and reduced supraorbital tori, which contrast sharply with the elongated, low-vaulted crania and prominent brows of Neanderthals. These features indicate enhanced neurocranial globularity and facial gracilization, adaptations possibly linked to dietary and cognitive shifts. This morphology shows continuity from earlier Homo heidelbergensis-like ancestors in , such as those from Bodo and (dated ~600,000–300,000 years ago), where intermediate robusticity evolves toward modern forms without clear species boundaries. Behavioral evidence from these sites underscores a gradual onset of modernity, exemplified by the processing and use of red ochre at Cave 13B in , dated to around 164,000 years ago, where over 500 pieces show grinding and scraping, likely for pigment production indicative of symbolic or ritualistic thought. This ochre use, combined with heat-treated silcrete tools at the site, reflects innovative resource exploitation without evidence of a sudden "cognitive revolution," instead pointing to incremental behavioral complexity building over millennia. Recent discoveries have addressed chronological gaps in the fossil record; for instance, a 2022 revision of the Omo Kibish I cranium from Ethiopia's Kibish Formation, using volcanic ash correlation and uranium-series dating, establishes a minimum age of over 233,000 years, predating previous estimates of ~195,000 years and confirming early Homo sapiens presence in during the Middle Pleistocene. This finding, alongside re-dating of associated sediments, fills a critical void between 300,000 and 200,000 years ago, reinforcing the African origin timeline.

Out-of-Africa Artifacts and Sites

Archaeological evidence from sites outside underscores the dispersal of anatomically modern humans, marked by the evolution and spread of sophisticated tool technologies. The transition from 's (MSA) to the in and beyond is exemplified by the adoption of bladelet technology, small blades less than 12 mm wide produced from prismatic cores, which emerged around 40,000 years ago and facilitated more efficient hunting and processing tools. This innovation, first appearing in late MSA contexts in before 60,000 years ago, spread rapidly along migration routes, becoming a hallmark of the in the and by approximately 45,000–42,000 years ago, indicating technological continuity and adaptation during out-of-Africa expansions. In Asia, key sites provide early evidence of modern human occupation and cultural practices. The Niah Cave in , dated to around 45,000 years ago, contains deep burials and artifacts such as human remains and stone tools, representing one of the oldest known anatomically modern human sites in island and demonstrating advanced funerary behaviors. Similarly, in yields stone tools from layers dated to 50,000–40,000 years ago, including blades and ornaments associated with industries, which coincide with genetic evidence of admixture between modern humans and Denisovans, highlighting interactions during early dispersals into Asia. European sites further illustrate the cultural modernity of these migrants through refined tools and symbolic art. At Kostenki in , Aurignacian blade technologies, characterized by elongated, retouched blades and burins, date to approximately 45,000 years ago, reflecting the rapid establishment of traditions in shortly after out-of-Africa migrations. By around 35,000 years ago, symbolic expressions emerged, as seen in Venus figurines—small carved statuettes of females, often with exaggerated features suggesting fertility or ritual significance—found across sites like Hohle Fels in , indicating the development of abstract thinking and artistic complexity among early European populations. The expansion reached the Americas via , with pre-Clovis sites challenging traditional timelines. in , occupied around 14,500 years ago, features preserved wooden artifacts, hearths, and plant remains, providing the earliest widely accepted evidence of settlement in and refuting the Clovis-first model that posited arrivals no earlier than 13,000 years ago. Even older traces appear at in , where footprints preserved in lakebed sediments date to 23,000–21,000 years ago, confirmed by of embedded seeds and grains, establishing a prolonged presence in well before Clovis cultures.

Historical Development and Debates

Early Paleoanthropological Theories

In the late , proposed that modern humans originated in , reasoning that the closest living relatives to humans— and chimpanzees—are native to that continent, suggesting a shared ancestral homeland there. This hypothesis, outlined in his 1871 book The Descent of Man, emphasized the continuity of primate distributions as evidence for human evolution's African roots, influencing subsequent paleoanthropological thought despite limited fossil evidence at the time. Contemporaries like , however, speculated on alternative origins, positing —specifically a hypothetical lost continent called in the —as the cradle of humanity based on perceived affinities with Asian apes like orangutans, thereby challenging Darwin's African focus and highlighting early regional debates. By the mid-20th century, fossil discoveries in strengthened the case for continental origins. The —Louis, Mary, and their sons—unearthed key specimens at in during the 1950s and 1960s, including the 1959 find of Australopithecus boisei (initially called Zinjanthropus) and subsequent fossils dated to around 1.8–2.0 million years ago, which Louis interpreted as early tool-using ancestors linking African hominins to modern humans. These discoveries shifted emphasis from Asian candidates like Pithecanthropus (later ) to African lineages, portraying as a pivotal species in the sapiens trajectory. F. Clark Howell, in his 1960s syntheses such as the edited volume African Ecology and Human Evolution (1963), integrated these finds with ecological data to advocate a unified African origin for sapiens, dismissing Asian-centric models and promoting multidisciplinary approaches that underscored 's role as the primary evolutionary theater. Fossil-centric debates further reinforced African connections, exemplified by the (Kabwe) skull from , discovered in 1921 and later dated to approximately 300,000 years ago, which exhibited archaic features bridging earlier hominins to anatomically modern humans and was seen as evidence of an African sapiens lineage. However, without genetic evidence, these interpretations coexisted with polycentric views, such as Carleton Coon's 1962 proposal in The Origin of Races that modern human races evolved independently from regional populations across multiple continents, reflecting the era's reliance on morphology alone and the absence of molecular tools to test single-origin hypotheses.

Rise of Genetic and Multiregional Alternatives

In the 1980s, molecular genetic evidence began to reshape debates on modern human origins, with a landmark study by Cann, Stoneking, and Wilson analyzing mitochondrial DNA (mtDNA) from diverse global populations. Their phylogenetic tree rooted the common ancestor of all modern human mtDNA lineages—termed "Mitochondrial Eve"—in Africa approximately 200,000 years ago, providing strong support for the recent African origin (RAO) model and challenging earlier views of regional continuity. This work revived interest in an African dispersal scenario by demonstrating greater genetic diversity in African populations and a recent out-of-Africa expansion, influencing subsequent genetic research. Confirmation came in the 1990s through Y-chromosome studies, which traced the patrilineal , or "," to around 188,000 years ago (with a 95% of 51,000–411,000 years). Hammer's analysis of Y-chromosome markers in global samples estimated a recent common ancestry consistent with African origins, aligning with mtDNA findings and further bolstering the RAO framework against multiregional alternatives. These genetic breakthroughs shifted the emphasis from fossil morphology to molecular clocks, highlighting 's primacy in human . The multiregional hypothesis, initially articulated by Weidenreich in the 1940s based on fossil continuities in and Europe, posited regional evolution of modern humans from local archaic populations maintained by gene flow. Refined by Wolpoff and colleagues in the , it emphasized across continents with interbreeding preventing , but RAO proponents critiqued it for underemphasizing Africa's higher and the recency of non-African lineages. As a compromise, assimilation models emerged in the , proposed by Bräuer, integrating RAO's African primacy with limited archaic admixture from regional populations like . These hybrids suggested modern humans primarily originated in but incorporated small contributions—around 4% Neanderthal DNA in non-Africans—from Eurasian archaics during dispersals. Recent genomic studies support a limited assimilation version, confirming low-level without undermining the core RAO timeline. Advances in during the have reinforced RAO while weakening strong multiregional claims. For instance, the ~45,000-year-old Ust'-Ishim from shows it as an early non-African with basal Eurasian ancestry and post-divergence admixture, indicating a rapid out-of-Africa spread without significant regional continuity from local archaics. Recent modeling studies as of 2023 further support a pan-African population structure for H. sapiens origins, with ongoing fossil discoveries through 2025 confirming Africa's central role without major shifts in the RAO versus multiregional debate. Such findings, combined with expanded analyses, underscore Africa's role as the source of modern human diversity, with limited archaic inputs occurring after initial dispersals.

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