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.

Multiregional evolution holds that the human species first arose around two million years ago and subsequent human evolution has been within a single, continuous human species. This species encompasses all archaic human forms such as Homo erectus, Denisovans, and Neanderthals as well as modern forms, and evolved worldwide to the diverse populations of anatomically modern humans (Homo sapiens).

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. Proponents of multiregionalism point to fossil and genomic data and continuity of archaeological cultures as support for their hypothesis.

The multiregional hypothesis was first proposed in 1984, and then revised in 2003. 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 is not currently the most accepted theory of modern human origin among scientists. "The African replacement model has gained the widest acceptance owing mainly to genetic data (particularly mitochondrial DNA) from existing populations. This model is consistent with the realization that modern humans cannot be classified into subspecies or races, and it recognizes that all populations of present-day humans share the same potential." The African replacement model is also known as the "out of Africa" theory, which is currently the most widely accepted model. It proposes that Homo sapiens evolved in Africa before migrating across the world." And: "The primary competing scientific hypothesis is currently recent African origin of modern humans, which proposes that modern humans arose as a new species in Africa around 100-200,000 years ago, moving out of Africa around 50-60,000 years ago to replace existing human species such as Homo erectus and the Neanderthals without interbreeding.Liu, Hua; et al. (2006). "A Geographically Explicit Genetic Model of Worldwide Human-settlement History". American Journal of Human Genetics 79 (2): 230–237. doi:10.1086/505436. PMID 16826514. Weaver, Timothy D.; Roseman, Charles C. (2008). "New developments in the genetic evidence for modern human origins". Evolutionary Anthropology: Issues, News, and Reviews (Wiley-Liss) 17 (1): 69–80. doi:10.1002/evan.20161. http://www3.interscience.wiley.com/journal/117921411/abstract.Fagundes, N. J.; Ray, N.; Beaumont M.; Neuenschwander, S. Salzano, F. M.; Bonatto, S. L.; Excoffier, L. (2007). "Statistical evaluation of alternative models of human evolution". Proc Natl Acad Sci USA 104 (45): 17614–9. doi:10.1073/pnas.0708280104. PMID 17978179. PMC 2077041. Bibcode: 2007PNAS..10417614F. https://www.pnas.org/doi/10.1073/pnas.0708280104Wolpoff, Milford, and Caspari, Rachel (1997). Race and Human Evolution. Simon & Schuster. p. 42. This differs from the multiregional hypothesis in that the multiregional model predicts interbreeding with preexisting local human populations in any such migration."Scholarly Community Encyclopeda.

History

Overview The Multiregional hypothesis was proposed in 1984 by Milford H. Wolpoff, Alan Thorne and Xinzhi Wu.Wolpoff, M. H.; Wu, X. Z.; Alan, G.; G. Thorne (1984). "Modern Homo sapiens Origins: A General Theory of Hominid Evolution Involving the Fossil Evidence from east Asia". The Origins of Modern Humans, New York: Liss, 411–83. Wolpoff credits Franz Weidenreich's "Polycentric" hypothesis of human origins as a major influence, but cautions that this should not be confused with polygenism, or Carleton Coon's model that minimized gene flow. According to Wolpoff, multiregionalism was misinterpreted by William W. Howells, who confused Weidenreich's hypothesis with a polygenic "candelabra model" in his publications spanning five decades:

Through the influence of Howells, many other anthropologists and biologists have confused multiregionalism with polygenism i.e. separate or multiple origins for different populations. 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.Wolpoff, M. H.; Caspari, R. 1997. Race and human evolution: A fatal attraction. New York: Simon and Schuster.Wolpoff, M. H.; Caspari, R. (2000). "The Many Species of Humanity". Przegląd Antropologiczny 63(1): 3–17. Wolpoff has also defended Wiedenreich's Polycentric hypothesis from being labeled polyphyletic. Weidenreich himself in 1949 wrote: "I may run the risk of being misunderstood, namely that I believe in polyphyletic evolution of man".Weidenreich, F. (1949). "Interpretations of the fossil material". In: Early Man in the Far East: Studies in Physical Anthropology. Howells, W. W. (ed). "Studies in Physical Anthropology" series, Vol. 1. Detroit: American Association of Physical Anthropologists. pp. 149–57.

In 1998, Wu founded a China-specific Multiregional model called "Continuity with [Incidental] Hybridization".Rosenberg, K. R.; Wu, X. (2013). "A River Runs through It: Modern Human Origins in East Asia". In: The Origins of Modern Humans: Biology Reconsidered. Smith, F. H (ed). Wiley-Blackwell. pp. 89–122. Wu's variant only applies the Multiregional hypothesis to the East Asian fossil record, and is popular among Chinese scientists.Liu, L.; Chen, X. (2012). The Archaeology of China: From the Late Paleolithic to the Early Bronze Age. Cambridge University Press. p. 14: "the majority of Chinese archaeologists and palaeontologists support the multiregional development model, proposing a hypothesis of regional continuity with hybridization between immigrants and indigenous populations in the evolution from H. erectus to H. sapiens in East Asia." However, James Leibold, a political historian of modern China, has argued the support for Wu's model is largely rooted in Chinese nationalism.Leibold, J. (2012). "Filling in the Nation: The Spatial Trajectory of Prehistoric Archaeology in Twentieth-century China", in Transforming History: The Making of a Modern Academic Discipline in Twentieth Century China, eds. Brian Moloughney and Peter Zarrow, pp. 333–71 (Hong Kong: Chinese University Press). Outside of China, the Multiregional hypothesis has limited support, held only by a small number of paleoanthropologists.Begun, D. R. (2013). "The Past, Present and Future of Palaeoanthropology". In: A Companion to Paleoanthropology. Wiley-Blackwell. p. 8: "It needs to be noted, however, that this [Multiregional model] is a minority view among paleoanthropologists, most of whom support the African replacement model."

"Classic" vs "weak" multiregionalism 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 1980s and 1990s.Stringer, C. B. (1992). "Replacement, continuity and the origin of Homo sapiens". In: Continuity or Replacement? Controversies in Homo sapiens Evolution. F. H. Smith (ed). Rotterdam: Balkema. pp. 9–24.Bräuer, G.; Stringer, C. (1997). "Models, polarization, and perspectives on modern human origins". In: Conceptual Issues in Modern Human Origins Research. New York: Aldine de Gruyter. pp. 191–201. Stringer describes how he considers the original Multiregional hypothesis to have been modified over time into a weaker variant that now allows a much greater role for Africa in human evolution, including anatomical modernity (and subsequently less regional continuity than was first proposed).

Stringer 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".

Genetic studies 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 2002, 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. This meant that even if our male line (Y chromosome) and our female line (mitochondrial DNA) came out of Africa in the last 100,000 years or so, we have inherited other genes from populations that were already outside of Africa. Since this study other studies have been done using much more data (see Phylogeography).

Fossil evidence

Morphological clades

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). Wolpoff cautions that the continuity in certain skeletal features in these regions should not be seen in a racial context, instead calling them morphological clades; defined as sets of traits that "uniquely characterise a geographic region". According to Wolpoff and Thorne (1981): "We do not regard a morphological clade as a unique lineage, nor do we believe it necessary to imply a particular taxonomic status for it". Critics of multiregionalism have pointed out that no single human trait is unique to a geographical region (i.e. confined to one population and not found in any other) but Wolpoff et al. (2000) note that regional continuity only recognizes combinations of features, not traits if individually accessed, a point they elsewhere compare to the forensic identification of a human skeleton:

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 2001 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.

Indonesia, Australia