One of the most common questions is how to differentiate the Multiregional evolution hypothesis from the Out of Africa hypothesis. The difference between the hypotheses is in which Pleistocene people were our ancestors, and which were not. Anthropologists consider many more detailed sources of evidence about human origins, but many sources of evidence fall into one or more of these basic categories. This combination of facts is a bit puzzling, and both hypotheses account for them a bit differently. Under the Out of Africa hypothesis, the first humans to leave Africa 1.
Both agree that Homo erectus originated in Africa and expanded to Eurasia about one million years ago, but Babyj vid differ in explaining the origin of modern humans Homo sapiens sapiens. Nature Genetics. Chimpanzee—human Gorilla—human Orangutan—human Gibbon—human. Initial analysis of Y chromosome DNA, which like mitochondrial DNA, is inherited from only one parent, was consistent with a recent African replacement model. Shovel-shaped incisors are commonly cited as evidence for regional continuity Banging heads China. These factors gave Africa a dominant role in the ancestry of today's human population. Strong gene flow Multl-regional migration swamping would likely have erased most morphological evidence for Multi-regional model continuity, but Multiregionalists point out that nodel flow throughout the Pleistocene was reduced at the "edges" unlike the center, where Africa received gene flow that was more multidirectional   to explain how morphological clades persisted at the peripheries of the Old World:. A analysis of mitochondrial DNA from people by Cann et al. The Comment you have entered exceeds the maximum Multi-regional model.
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Anthropos Brno. In: G. Evolutionary Anthropology. Smith, F. Archaic human Multi-regioal. August Stringer eds. Because of the random nature of genetic drift, some traits will retain regional continuity in the face of the overall Lesbian bully video of Multi-regional model flow. Gill; Geoffrey Clark Category Commons. Also see map ; may resize browser window. Wolpoff liken the evolution of human modernity to throwing pebbles into a pond:.
The multiregional hypothesis , multiregional evolution MRE , or polycentric hypothesis is a scientific model that provides an alternative explanation to the more widely accepted "Out of Africa" model of monogenesis for the pattern of human evolution.
- One of the most common questions is how to differentiate the Multiregional evolution hypothesis from the Out of Africa hypothesis.
- Multiregionalism or the Multiregional Evolution MRE hypothesis is a model of Pleistocene human evolution , which argues the human species emerged in Africa 2 million years ago, and "developed their modern forms in every area of the Old World".
- The Multiregional Hypothesis model of human evolution abbreviated MRE and known alternatively as Regional Continuity or Polycentric model argues that our earliest hominid ancestors specifically Homo erectus evolved in Africa and then radiated out into the world.
- The multiregional hypothesis , multiregional evolution MRE , or polycentric hypothesis is a scientific model that provides an alternative explanation to the more widely accepted "Out of Africa" model of monogenesis for the pattern of human evolution.
Multiregionalism or the Multiregional Evolution MRE hypothesis is a model of Pleistocene human evolution , which argues the human species emerged in Africa 2 million years ago, and "developed their modern forms in every area of the Old World".
Neanderthals by these African migrants across the Old World, with negligible to no genetic admixture within the last , years. The MRE model is often misinterpreted as the polyphyletism, or evolutionary polygenism    of races , when as Multiregionalists explain:.
Multiregionalism denies a speciation event in the last 2 mya, and sinks H. It has been observed that by the "late s most paleoanthropologists were interpreting the fossil and genetic evidence as incompatible with a 'strong' version of the multiregional hypothesis"  subsequently Multiregionalists revised their model to allow for a dominant role for Africa during Pleistocene human evolution Wolpoff et al.
Multiregionalists such as Milford H. Wolpoff liken the evolution of human modernity to throwing pebbles into a pond:. In other words, Multiregionalists do not think modern humans evolved in one region or anatomical modernity evolved as a single "bio-package", but that modern traits as a process appeared individually in separate populations at different times, not limited to Africa, and spread through gene flow.
The revised model now recognizes the vast majority but not all of anatomical traits  associated with modernity evolved in Africa, which had the largest population size throughout the Pleistocene:. Although MRE has always maintained more gene flow came from Africa given its larger population size    MRE 1 did not credit Africa as having a dominant role in human evolution and anatomical modernity.
Wolpoff cautions in his view "this does not mean that modernity dispersed with Africans". Chris Stringer, regards this dispute to be almost meaningless, i.
Multiregionalism proposes there was a distinct pattern of morphological continuity in the furthest regions from Africa the "edges" for over 1 million years, when these areas were settled by H. To explain how these complexes of skeletal traits persisted for so long and unchanged in these Old World peripheral populations, Multiregionalists do not propose parallel evolution i.
In , Alan Thorne attempted to solve this paradox: "how did populations retain geographical distinctions and yet evolve together? Thorne realized that isolation is not necessary for long-term marked phenotypic differentiation if the peripheral populations of a species range are small.
This is because genetic drift will reduce variation in large populations, drift has less effect , and selection will increase because the peripheries of a species range are least ecologically optimal and most harsh. Conversely, in optimal environments where a species originated usually always at the center of a species geographical distribution and has adapted the longest - selection is relaxed and more trait variants can flourish.
Reduced variation in peripheral populations can result in monomorphism, meaning intraregional homogeneity in phenotype, where virtually all individuals look very similar.
According to Wolpoff and colleagues, regional continuity skeletal traits were maintainable at the peripheries with gene flow if there was a stable interaction between genetic drift, gene flow and selection.
Strong gene flow through migration swamping would likely have erased most morphological evidence for regional continuity, but Multiregionalists point out that gene flow throughout the Pleistocene was reduced at the "edges" unlike the center, where Africa received gene flow that was more multidirectional   to explain how morphological clades persisted at the peripheries of the Old World:. More recently, MRE 2 posits migration swamping occurred across the Old World throughout the Pleistocene because of the larger population in Africa:.
Note that whereas gene flow affects all traits equally, genetic drift has a different expectation for each trait. It is a key tenet of Multiregional evolution that in the fossil record at these geographical peripheries there should be evidence of skeletal continuity "spanning the period before and after the replacement time"  of the competing RAO hypothesis.
Each periphery is said to contain a distinguishing co-occurring set of morphological traits, "a consequence of the colonization events that limited peripheral variability, primarily because of drift and bottlenecking".
Regional continuity is not the claim individual traits do not appear in other regions, only combinations  of features:. Compared to other contemporary populations, the Javan [Indonesian] people have a distinctive combination of cranial features.
These include 1 thickened vault bones, 2 a long, flattened frontal squama whose anterior edge merges into 3 strong, continuous browridges forming an almost or straight bar of bone across the orbits, 4 a posterior position for the minimum frontal breadth, and 5 a prebregmatic eminence. Facial features can be generally described as involving 6 large projecting faces with 7 massive, rounded cheekbones, specially the males, facing in an anterolateral direction; 8 postcanine teeth are among the largest to be found anywhere that time, and while large postcanin teeth can befound in all Pleistocene populations, it is interesting that, holding sex constant, average postcanine tooth size does not change in this clade until the Holocene, making 9 pattern of dental reduction an additional regional feature.
Details of the face include 10 a 'rolled edge' on the lower margin of the orbits, 11 a distinctive ridge on the cheek at the zygomaxillar suture, and 12 a nasal floor that flows out smoothly onto the face.
In the case of this aspect of nasal floor anatomy, other later population such as some modern Africans also possess the feature. What makes it important here is the fact that it characterizes the Australasian peoples both in the past and today in combination with the other features we have found. The presence of this complex of features distinguishes the fossil Javans from groups in other areas. After all, the humans we have compared belong to the same species, and we can hardly expect that, within species, regional groups can be characterized by single unique features that do not appear elsewhere.
The regional continuity traits essential to MRE are not autapomorphic unique derived traits via mutation , diagnostic for a reproductively isolated population ; Wolpoff explains: "if single traits clearly reflected the evolutionary sequence in different regions, it would be a disproof of Multiregional evolution because it would suggest there was no network of genetic exchanges linking populations". Heterogeneity at the species center i. Africa would mean such unique "edge" morphological combinations would not appear there given the extremely high variation and countless number of variant combinations of features, e.
Although all the traits a - z individually would be present in African fossils, this point is often misunderstood or overlooked see below. There are individual traits that show a disparate frequency by region, i.
These exceptional singular traits such as the H-O mandibular foramen in Europe which appears in only a single Pleistocene fossil in Africa  Wolpoff maintains are strong evidence for regional continuity, but because they are such few in number, MRE literature focuses on combinations.
The latter also rule out homoplasies : "the double evolution of a whole set of features is improbable to the extreme". Groves tested 16 of Wolpoff's regional continuity traits for North China and 9 for Java, Indonesia.
He found none to be exclusive to either these regions, with high overlap of frequency occurrence, concluding: "the Regional Continuity model [MRE] lacks much real substance". Lahr , and Lieberman published similar findings. These studies have been criticized by Wolpoff who notes they only tested traits individually, not combinations i. In two studies by Habgood , it was shown a limited number of traits combined might lend support to regional continuity: a unique set of 5 traits in North China associated with facial flatness 1.
Evidence for this small yet consequential and not trivial skeletal continuity better fits the Assimilation model AM than MRE: "AM differs from MRE by positing that the archaic contribution to modern populations was always relatively small, and thus continuity would only be found in limited details of anatomy". More recent critics of regional continuity point out that the combinations of morphological traits thought to be unique and circumscribed to the 3 peripheries by Multiregionalists, are in fact common in the African fossil record, or occasionally in other regions, e.
Habgood still sees evidence for minor regional skeletal continuity, but proponents of the RAO hypothesis continue to deny any morphological continuity at the Old World peripheries between archaic humans and early moderns before and after the replacement time by African migrants.
A re-analysis of regional continuity traits listed by MRE proponents for Indonesia and the surrounding Australian region found:. Part of this dismissal of regional continuity was the result of a new reconstruction of the Sangiran 17 skull from Java, which removed the marked facial prognathism and zygomaxillary tuberosity of Wolpoff's reconstruction.
Research by Brown has highlighted the possibility the flat frontal bones in terminal Pleistocene Australian crania, are artificial deformations. This is problematic for Multiregionalists who cite a flat frontal bone as an indicator of morphological continuity from archaic Indonesians. Phenotype is an expression of genes, and so it has been calculated the sizable number of MRE continuity features in each periphery - yield estimates of archaic genetic admixture such as Neanderthal , ranging from The three morphological clades of the Pleistocene have been called races or allotaxa by Wolpoff, defined as "morphologically diagnosable yet not reproductively isolated populations".
This is said to have occurred through population size changes at the peripheries populations were no longer small , increased gene flow, and Neolithic demic-replacements:. One consequence is that today variation within populations is greater than variation between populations, and subspecies biological races do not exist [ Modern paleoanthropology and genetics are among the disciplines that have shown that there is no taxonomy in the human species below the species level.
They also show that the present poorly reflects the past. Neandertal morphology and genetics, and genetic evidence of other distinct groups, suggest far more population structure in the past. It is likely that for much of the Pleistocene the human species had races. But, whether or not races appeared in the past, they did not persist. With only some exceptions, much of the Pleistocene human variation did not survive the enormous population expansions and replacements of the latest Pleistocene and Holocene.
Wu also informs the: "Holocene should have rendered a lot of morphological changes in human skulls and made some of the common features which have existed in Pleistocene China, that no longer exist in recent Chinese populations". Jump to: navigation , search. Ripples from the pebbles can spread across the entire pond surface; the interconnections of the populations provide the pathways for the traits to spread. However, supporters of the MRE model have more recently accepted the possibility that the majority of the modern human gene pool could have an African origin Wolpoff et al.
Because of the random nature of genetic drift, some traits will retain regional continuity in the face of the overall impact of gene flow.
It is found in almost no other remains There are no specific regional characteristics that demonstrate an unequivocal link between the Sangiran or Ngandong fossils and early Australians.
In reporting that the model as he misconstrues it could not work, Lewin cites the geneticist Rouhani , who asserts that the model could not work, and we concur with this assessment because Rouhani has also addressed Coon's model of parallel, independent evolution of human races and not multiregional evolution.
Wolpoff and colleagues considered this a persistent pattern throughout the Pleistocene; the continued movement of genes from the center brought new adaptive genes to the peripheries, where regionally predominant features were also maintained, and at no time did African features fully replace the regionally predominant ones.
It was argued that each inhabited area showed a continuous anatomic sequence leading to modern humans, and those outside Africa showed no special African influence. Thus, modern populations would mainly have African-derived genes and African-derived morphological characters, although these were predominantly acquired through gene flow, rather than rapid replacement.
Multiregional Evolution explains Pleistocene variation as a consequence of population structure in this small, widespread species, whose populations were intermittently connected in a network of gene flow and population movements.
Eller and colleagues suggest it is likely that half or more of the human species lived in Africa, and some estimate the African percentage was even higher Mele et al. This superimposes the multiregional pattern throughout the human range, with the direction of gene flow across this interconnected network most often from the center of the human range, where there were more people, to the various edges Wolpoff, There is no evidence of specific admixture with Africans at any time, let alone replacement by them' Multiregionalism gave Africa no special place in our evolution.
This is the apparent paradox that Multiregional evolution addresses. In: Henke, W. Handbook of Paleoanthropology vol. New York: Springer. It is not the claim that such features do not appear elsewhere; the genetic structure of the human species makes such a possibility unlikely to the extreme. There may be uniqueness in combinations of traits, but no single trait is likely to have been unique in a particular part of the world although it might appear to be so because of the incomplete sampling provided by the spotty human fossil record.
Why do clusters of features occur in combination? There are several possible reasons: a they are consequences of a single pleiotropic gene, or tightly linked genetically, b they form part of a developmental complex, c they form part of functional complex, d they are selected for by common environmental factors, and e they occur together by chance But with the breadth and consistency of the latest research, this strong version of multiregionalism is falsified.
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Lahr , and Lieberman published similar findings. These include 1 thickened vault bones, 2 a long, flattened frontal squama whose anterior edge merges into 3 strong, continuous browridges forming an almost or straight bar of bone across the orbits, 4 a posterior position for the minimum frontal breadth, and 5 a prebregmatic eminence. Princeton: Princeton University Press. This is said to have occurred through population size changes at the peripheries populations were no longer small , increased gene flow, and Neolithic demic-replacements:. Encyclopedia of Quaternary Science Second Edition. When in the early 20th century numerous hominins with robust large-brained skulls and heavy brow ridges now usually characterized as H.
Multi-regional model. Navigation menu
The hypothesis contends that the mechanism of clinal variation through a model of "Centre and Edge" allowed for the necessary balance between genetic drift , gene flow and selection throughout the Pleistocene, as well as overall evolution as a global species, but while retaining regional differences in certain morphological features.
The multiregional hypothesis was first proposed in , and then revised in In its revised form, it is similar to the Assimilation Model, which holds that modern humans originated in Africa and today share a predominant recent African origin, but have also absorbed small, geographically variable, degrees of admixture from other regional archaic hominin species.
The Multiregional hypothesis was proposed in by Milford H. Wolpoff , Alan Thorne and Xinzhi Wu. Howells , who confused Weidenreich's hypothesis with a polygenic "candelabra model" in his publications spanning five decades:.
How did Multiregional evolution get stigmatized as polygeny? We believe it comes from the confusion of Weidenreich's ideas, and ultimately of our own, with Coon's. The historic reason for linking Coon's and Weidenreich's ideas came from the mischaracterizations of Weidenreich's Polycentric model as a candelabra Howells, , , , , that made his Polycentric model appear much more similar to Coon's than it actually was.
Through the influence of Howells, many other anthropologists and biologists have confused multiregionalism with polygenism i. Alan Templeton for example notes that this confusion has led to the error that gene flow between different populations was added to the Multiregional hypothesis as a "special pleading in response to recent difficulties", despite the fact: "parallel evolution was never part of the multiregional model, much less its core, whereas gene flow was not a recent addition , but rather was present in the model from the very beginning"  emphasis in original.
Despite this, multiregionalism is still confused with polygenism, or Coon's model of racial origins, from which Wolpoff and his colleagues have distanced themselves. Weidenreich himself in wrote: "I may run the risk of being misunderstood, namely that I believe in polyphyletic evolution of man". Chris Stringer , a leading proponent of the more mainstream recent African origin theory , debated Multiregionalists such as Wolpoff and Thorne in a series of publications throughout the late s and s.
Stringer distinguishes the original or "classic" Multiregional model as having existed from its formulation until , to a "weak" post variant that has "shifted close to that of the Assimilation Model".
The finding that " Mitochondrial Eve " was relatively recent and African seemed to give the upper hand to the proponents of the Out of Africa hypothesis. But in , Alan Templeton published a genetic analysis involving other loci in the genome as well, and this showed that some variants that are present in modern populations existed already in Asia hundreds of thousands of years ago.
Since this study other studies have been done using much more data see Phylogeography. Proponents of the multiregional hypothesis see regional continuity of certain morphological traits spanning the Pleistocene in different regions across the globe as evidence against a single replacement model from Africa.
In general, three major regions are recognized: Europe , China , and Indonesia often including Australia. Regional continuity There may be uniqueness in combinations of traits, but no single trait is likely to have been unique in a particular part of the world although it might appear to be so because of the incomplete sampling provided by the spotty human fossil record.
Combinations of features are "unique" in the sense of being found in only one region, or more weakly limited to one region at high frequency very rarely in another. Wolpoff stresses that regional continuity works in conjunction with genetic exchanges between populations. Long-term regional continuity in certain morphological traits is explained by Alan Thorne 's "Centre and Edge"  population genetics model which resolves Weidenreich's paradox of "how did populations retain geographical distinctions and yet evolve together?
For example, in Wolpoff and colleagues published an analysis of character traits of the skulls of early modern human fossils in Australia and central Europe. They concluded that the diversity of these recent humans could not "result exclusively from a single late Pleistocene dispersal", and implied dual ancestry for each region, involving interbreeding with Africans.
Thorne held that there was regional continuity in Indonesia and Australia for a morphological clade. In , Andrew Kramer tested 17 proposed morphological clade features. He found that: "a plurality eight of the seventeen non-metric features link Sangiran to modern Australians" and that these "are suggestive of morphological continuity, which implies the presence of a genetic continuum in Australasia dating back at least one million years"  but Colin Groves has criticized Kramer's methodology, pointing out that the polarity of characters was not tested and that the study is actually inconclusive.
Phillip Habgood discovered that the characters said to be unique to the Australasian region by Thorne are plesiomorphic :. Many are also commonly found on the crania and mandibles of anatomically-modern Homo sapiens from other geographical locations, being especially prevalent on the robust Mesolithic skeletal material from North Africa.
Yet, regardless of these criticisms Habgood allows for limited regional continuity in Indonesia and Australia, recognizing four plesiomorphic features which do not appear in such a unique combination on fossils in any other region: a sagittally flat frontal bone, with a posterior position of minimum frontal breadth, great facial prognathism, and zygomaxillary tuberosities. Wolpoff, initially skeptical of Thorne's claims, became convinced when reconstructing the Sangiran 17 Homo erectus skull from Indonesia, when he was surprised that the skull's face to vault angle matched that of the Australian modern human Kow Swamp 1 skull in excessive prognathism.
Durband in contrast states that "features cited as showing continuity between Sangiran 17 and the Kow Swamp sample disappeared in the new, more orthognathic reconstruction of that fossil that was recently completed". Xinzhi Wu has argued for a morphological clade in China spanning the Pleistocene, characterized by a combination of 10 features.
Liujiang and recent Chinese. Habgood in criticized Wu's list, pointing out that most of the 10 features in combination appear regularly on fossils outside China. However, according to Chris Stringer , Habgood's study suffered from not including enough fossil samples from North Africa, many of which exhibit the small combination he considered to be region-specific to China.
Facial flatness as a morphological clade feature has been rejected by many anthropologists since it is found on many early African Homo erectus fossils, and is therefore considered plesiomorphic,  but Wu has responded that the form of facial flatness in the Chinese fossil record appears distinct to other i.
Shovel-shaped incisors are commonly cited as evidence for regional continuity in China. They discuss the fact that there are different degrees of "shovelled" e.
Smith also emphasizes that: "It is the pattern of shoveling that identities as an East Asian regional feature, not just the occurrence of shoveling of any sort". Since the early s, David W. Frayer has described what he regards as a morphological clade in Europe.
Although many anthropologists consider Neanderthals and Cro Magnons morphologically distinct,   Frayer maintains quite the opposite and points to their similarities, which he argues is evidence for regional continuity:.
Frayer et al. Regarding the latter, Frayer observes a sequence of nasal narrowing in Neanderthals, following through to late Upper Palaeolithic and Holocene Mesolithic crania. His claims are disputed by others,  but have received support from Wolpoff, who regards late Neanderthal specimens to be "transitional" in nasal form between earlier Neanderthals and later Cro Magnons.
More recent claims regarding continuity in skeletal morphology in Europe focus on fossils with both Neanderthal and modern anatomical traits, to provide evidence of interbreeding rather than replacement. Fossil remains of Graecopithecus found in Bulgaria and Greece have been dated to 7. A analysis of mitochondrial DNA from people by Cann et al.
Such a recent replacement scenario is not compatible with the Multiregional hypothesis and the mtDNA results led to increased popularity for the alternative single replacement theory.
Multiregionalists have responded to what they see as flaws in the Eve theory,  and have offered contrary genetic evidences.
Initial analysis of Y chromosome DNA, which like mitochondrial DNA, is inherited from only one parent, was consistent with a recent African replacement model. However, the mitochondrial and Y chromosome data could not be explained by the same modern human expansion out of Africa; the Y chromosome expansion would have involved genetic mixing that retained regionally local mitochondrial lines.
In addition, the Y chromosome data indicated a later expansion back into Africa from Asia, demonstrating that gene flow between regions was not unidirectional. An early analysis of 15 noncoding sites on the X chromosome found additional inconsistencies with the recent African replacement hypothesis.
The analysis found a multimodal distribution of coalescence times to the most recent common ancestor for those sites, contrary to the predictions for recent African replacement; in particular, there were more coalescence times near 2 million years ago mya than expected, suggesting an ancient population split around the time humans first emerged from Africa as Homo erectus , rather than more recently as suggested by the mitochondrial data.
While most of these X chromosome sites showed greater diversity in Africa, consistent with African origins, a few of the sites showed greater diversity in Asia rather than Africa.
For four of the 15 gene sites that did show greater diversity in Africa, the sites' varying diversity by region could not be explained by simple expansion from Africa, as would be required by the recent African replacement hypothesis.
Later analyses of X chromosome and autosomal DNA continued to find sites with deep coalescence times inconsistent with a single origin of modern humans,      diversity patterns inconsistent with a recent expansion from Africa,  or both.
In , a DNA study of more than 12, men from East Asian regions showed that all of them carry a mutation that originated in Africa about 35, to 89, years ago and these "data do not support even a minimal in situ hominid contribution in the origin of anatomically modern humans in East Asia".
In a review and analysis of the genetic lineages of 25 chromosomal regions, Alan Templeton found evidence of more than 34 occurrences of gene flow between Africa and Eurasia. Of these occurrences, 19 were associated with continuous restricted gene exchange through at least 1. Three were associated with the original expansion of Homo erectus out of Africa around 2 million years ago, 7 with an intermediate expansion out of Africa at a date consistent with the expansion of Acheulean tool technology, and a few others with other gene flows such as an expansion out of Eurasia and back into Africa subsequent to the most recent expansion out of Africa.
Recent analyses of DNA taken directly from Neanderthal specimens indicates that they or their ancestors contributed to the genome of all humans outside of Africa, indicating there was some degree of interbreeding with Neanderthals before their replacement.
By , extraction of DNA directly from some archaic human samples was becoming possible. However, "Out of Africa" Theory proponents also explain this with the fact that genetic changes occur on a regional basis rather than a continental basis, and populations close to each other are likely to share certain specific regional SNPs while sharing most other genes in common.
As we do not know the specific migration matrix, we are unable to input the exact data, which would answer these questions irrefutably. From Wikipedia, the free encyclopedia.
Hominin events for the last 10 million years. Hominin timeline. This box: view talk edit. Homo habilis. Homo erectus. Homo sapiens. Earlier apes. Gorilla split. Possibly bipedal. Chimpanzee split. Earliest bipedal. Stone tools. Exit from Africa. Earliest fire use. Earliest cooking. Earliest clothes. See also: Life timeline , and Nature timeline. Life timeline. Single-celled life. Multicellular life. Earliest water. Earliest life.
Earliest oxygen. Atmospheric oxygen. Oxygen crisis. Sexual reproduction. Earliest plants. Ediacara biota. Cambrian explosion. Earliest apes. See also: Human timeline , and Nature timeline. Main article: Archaic human admixture with modern humans. Archaic human admixture with modern humans Human evolution Human origins Mitochondrial Eve Nature timeline Phyletic gradualism Recent African origin of modern humans Y-chromosomal Adam. Bibcode : Sci The Human Lineage.
American Journal of Physical Anthropology. American Anthropologist. Human Evolution. Race and human evolution: A fatal attraction. New York: Simon and Schuster. Howells, W. Studies in Physical Anthropology; No.
Acta Anthropologica Sinica. Smith, F. Cambridge University Press. Brian Moloughney and Peter Zarrow, pp. In: A Companion to Paleoanthropology. This combination of facts is a bit puzzling, and both hypotheses account for them a bit differently. Under the Out of Africa hypothesis, the first humans to leave Africa 1. Species, of course, are defined by reproductive isolation, so the evolution of these several species of humans was separate.
The fossil archaic humans that we find throughout the Old World belonged to these several species, but only one branch of this ancient family tree could give rise to today's humanity. This branch was African. The origin of modern humans in Africa explains why today's Africans are more genetically variable than other populations they were the first human population to expand, and other populations like those of Europe and Asia were founded later.
The recent origin explains why today's human populations are genetically similar -- they haven't had time to diverge very much. The resemblances with archaic humans in some modern people are explained either as a result of parallel evolution the same selection in the same place leads to similar features or as a result of slight genetic contributions from archaic humans into today's populations.
Under the Multiregional evolution hypothesis, the first humans to leave Africa 1. Instead, these populations always exchanged genes with each other through recurrent gene flow. Today, we are part of this same species, which has evolved greatly over time to a very different morphology and behavior from the first humans.
The low genetic differences among human populations are a result of a history of gene flow between ancient populations. Our present morphology and behavior have greatly changed from archaic humans because of natural selection in a global human population. Resemblances between archaic and modern humans in some parts of the world are the result of ancestry.
The greater genetic variation within Africa is a consequence of larger African population size, greater ecological diversity and local selection, or both. These factors gave Africa a dominant role in the ancestry of today's human population. It was first posted in , and the science has changed a lot since then. We now have ancient DNA evidence from Neanderthals, early modern humans in Europe, and a handful of ancient samples from Africa.
Those have changed the picture substantially from the turn of the century.
Multiregional Hypothesis: Human Evolutionary Theory
The Multiregional Hypothesis model of human evolution abbreviated MRE and known alternatively as Regional Continuity or Polycentric model argues that our earliest hominid ancestors specifically Homo erectus evolved in Africa and then radiated out into the world.
Based on paleoanthropological data rather than genetic evidence, the theory says that after H. Homo sapiens , so MRE posits, evolved from several different groups of Homo erectus in several places throughout the world. However, genetic and paleoanthropological evidence gathered since the s has shown conclusively that that simply cannot be the case: Homo sapiens evolved in Africa and dispersed out into the world, somewhere between 50,, years ago.
What happened then is quite interesting. In the midth century, when Darwin wrote Origin of Species , the only lines of evidence of human evolution he had were comparative anatomy and a few fossils. The only hominin ancient human fossils known in the 19th century were Neanderthals , early modern humans , and H.
A lot of those early scholars didn't even think those fossils were humans or related to us at all. When in the early 20th century numerous hominins with robust large-brained skulls and heavy brow ridges now usually characterized as H. These arguments still had to be tied directly to the growing fossil record: again, no genetic data was available.
The predominant theory then was that H. As more and more distantly-related fossil hominins were identified in the s and s, such as Australopithecus , it became clear that human evolution was much older than previously considered and much more varied.
In the s and 60s, numerous hominins of these and other older lineages were found in East and South Africa: Paranthropus , H. The predominant theory then although it varied greatly from scholar to scholar , was that there were nearly independent origins of modern humans within the various regions of the world out of H.
Don't kid yourself: that original hardline theory was never really tenable -- modern humans are simply too much alike to be evolved from different Homo erectus groups, but more reasonable models such as those put forward by paleoanthropologist Milford H. Wolpoff and his colleagues argued that you could account for the similarities in human beings on our planet because there was lots of gene flow between these independently evolved groups. In the s, paleontologist W.
Howells argued that H. By the s, growing data from human genetics led Stringer and Andrews to develop a model that said that the very earliest anatomically modern humans arose in Africa about , years ago and archaic populations found throughout Eurasia might be descendants of H. The differences were stark and testable: if MRE was right, there would be various levels of ancient genetics alleles found in modern people in scattered regions of the world and transitional fossil forms and levels of morphological continuity.
If RAO was right, there should be very few alleles older than the origins of anatomically modern humans in Eurasia, and a decrease in genetic diversity as you get away from Africa.
Between the 's and today, over 18, whole human mtDNA genomes have been published from people all over the world, and they all coalesce within the last , years and all the non-African lineages only 50,, years old or younger. Any hominin lineage that branched off from the modern human species prior to , years ago did not leave any mtDNA in modern humans. Today, paleontologists are convinced that humans evolved in Africa and that the bulk of modern non-African diversity is recently derived from an African source.
The exact timing and pathways outside of Africa are still under debate, perhaps out of East Africa, perhaps along with a southern route from South Africa. The most startling news from a human evolution sense is some evidence for mixing between Neanderthals and Eurasians. The discovery of a completely new species called the Denisovans threw another stone in the pot: even though we have very little evidence of Denisovan existence, some of their DNA has survived in some human populations.
It is now clear that before we can understand the diversity in archaic humans, we have to understand the diversity in modern humans. Although MRE has not been seriously considered for decades, now it seems possible that modern African migrants hybridized with local archaics in different regions of the world. Genetic data demonstrate that such introgression did occur, but it is likely to have been minimal. Neither Neanderthals nor Denisovans survived into the modern period, except as a handful of genes, perhaps because they were unable to adapt to the unstable climates in the world or competition with H.
Share Flipboard Email. Kris Hirst. Kris Hirst is an archaeologist with 30 years of field experience. Updated March 05, Disotell TR. Archaic human genomics. American Journal of Physical Anthropology S55 Journal of Human Evolution Gamble C. In: Mock CJ, editor. Encyclopedia of Quaternary Science Second Edition. Amsterdam: Elsevier. The four faces of Eve: hypothesis compatibility and human origins.
Quaternary International Stringer C. Why we are not all multiregionalists now. Continue Reading.