Origins of Modern Humans
As it is usually presented, there are two major competing models on this subject – recent African origin and multiregional evolution. The debate concerns both the relative amount of replacement or interbreeding that occurred in areas outside of Africa, when waves of humans (or human ancestors) left it to colonize other areas, and the relative importance of more recent waves as opposed to more ancient ones.
The mainstream view, known as the recent African origin model, holds that all or nearly all modern human genetic diversity around the world can be traced back to the first anatomically modern humans to leave Africa. This model is supported by multiple and independent lines of evidence, such as the fossil record and genetics.
Historically, critics of this view are often bracketed together as holding a "multiregional hypothesis", which has waned in popularity since the early 1990s. Such critics argue that significant amounts of older non-African genetic lineages have survived in various parts of the world through inter-breeding with anatomically modern humans. According to strong versions of the multiregional model the various human populations around the world today will have surviving genetic material that goes back as far as early humans such as Homo erectus. A wide set of data in human evolutionary genetics (Jobling, Hurles and Tyler-Smith, 2004) strongly favour the “Out of Africa" model. Analyses of modern Europeans suggest that no mitochondrial DNA (direct maternal line) originating with Neanderthals has survived into modern times.
However the recent sequencing of the Neanderthal and Denisovan genomes shows some admixture. A draft sequence publication by the Neanderthal Genome Project in May 2010 indicates some form of hybridization between archaic humans and modern humans took place after modern humans emerged from Africa. An estimated 1 to 4 percent of the DNA in Europeans and Asians (i.e. French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA and not with Sub-Saharan Africans (i. e., Yoruba and San probands), while Melanesians have an additional 1-6% of Denisovan origin.
In practice, controversy is generally about specific periods and specific proposals for periods of such interbreeding. The existence and importance of gene flow out of Africa is generally accepted, while the possibility of isolated instances of inter-breeding between recent sub-Saharan arrivals and their less "modern" contemporaries at various stages of prehistory is not particularly controversial. Nonetheless, and according to recent genetic studies, modern humans seem to have mated with "at least two groups" of ancient humans: Neanderthals and Denisovans.
Read more about this topic: Anatomically Modern Humans
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