Anatomically modern humans
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The term anatomically modern humans (AMH, also AMHS for "anatomically modern Homo sapiens") in paleoanthropology refers to individuals of Homo sapiens with an appearance consistent with the range of phenotypes in modern humans.
Anatomically modern humans evolved from archaic Homo sapiens in the Middle Paleolithic, about 200,000 years ago. The emergence of anatomically modern human marks the dawn of the subspecies Homo sapiens sapiens, i.e. the subspecies of Homo sapiens that includes all modern humans. The oldest fossil remains of anatomically modern humans are the Omo remains, which date to 195,000 (±5,000) years ago and include two partial skulls as well as arm, leg, foot and pelvis bones.
Anatomically modern humans are distinguished from their immediate ancestors, archaic Homo sapiens, by a number of anatomical features. Archaic Homo sapiens had robust skeletons, indicating that they lived a physically demanding life; this may mean that anatomically modern humans, with their more gracile frames, had become more dependent on technology than on raw physical power to meet the challenges of their environment.
Archaic Homo sapiens also had very prominent brow ridges (protruding layers of bone above the eye socket). With the emergence of anatomically modern humans, the brow ridges had significantly reduced, and in modern humans they are, on average, barely visible. Another distinguishing feature of AMH is a prominent chin, something which is lacking in archaic Homo sapiens.
AMH commonly have a vertical forehead whereas their predecessors had foreheads that sloped backwards. According to Desmond Morris, the vertical forehead in humans not only houses larger brains, but the prominent forehead plays an important role in human communication through eyebrow movements and forehead skin wrinkling.
Early modern humans
The Omo, Herto, Skhul, and Jebel Qafzeh remains are sometimes referred to as "Early Modern Humans" because their skeletal remains exhibit a mix of archaic and modern traits. Skhul V, for example, has prominent brow ridges and a projecting face. However, the brain case of Skhul V is distinct from that of the Neanderthals and is similar to the brain case of modern humans.
In Europe, the early modern humans were the Cro-Magnon.
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.
Modern human behavior
There is considerable debate regarding whether the earliest anatomically modern humans behaved similarly to recent or existing humans. Modern human behaviors characteristic of recent humans include fully modern language, the capacity for abstract thought and the use of symbolism to express cultural creativity. There are two opposing hypotheses regarding the origins of modern behavior. Some scholars argue that humans achieved anatomical modernity first, around 200kya, and only later did they adopt modern behaviors around 50kya. This hypothesis is based on the limited record of fossils from periods before 50kya and the abundance of human artifacts found after 50kya.[further explanation needed] Proponents of this view distinguish "anatomically modern humans" from "behaviorally modern humans".
The opposing view is that humans achieved anatomical and behavioral modernity simultaneously. For example, proponents of this view argue that humans had evolved a lightly built skeleton during the transition to anatomical modernity, and this could have only occurred through increased human cooperation and the increased use of technology, traits characteristic of modern behavior.
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- Homo sapiens – Museum of Natural History