Modern humans are theorized to have evolved from archaic humans, who in turn evolved from Homo erectus. Varieties of archaic humans are sometimes included under the binomial name "Homo sapiens" because their brain size is very similar to that of modern humans. Archaic humans had a brain size averaging 1200 to 1400 cubic centimeters, which overlaps with the range of modern humans. Archaics are distinguished from anatomically modern humans by having a thick skull, prominent brow ridges and the lack of a prominent chin.
Homo rhodesiensis "Broken Hill Cranium": dated to either 130,000 years ago (using amino acid racemization determination) or 800,000 to 600,000 years ago (within the same time as Homo erectus), depending on which dating method is used.
Anatomically modern humans appear from about 200,000 years ago and after 70,000 years ago (see Toba catastrophe theory) gradually marginalize the "archaic" varieties. Non-modern varieties of Homo are certain to have survived until after 30,000 years ago, and perhaps until as recent as 10,000 years ago. Which of these, if any, are included under the term "archaic human" is a matter of definition and varies among authors. Nonetheless, according to recent genetic studies, modern humans may have bred with "at least two groups" of ancient humans: Neanderthals and Denisovans. Other studies have cast doubt on admixture being the source of the shared genetic markers between archaic and modern humans, pointing to an ancestral origin of the traits originating 500,000 to 800,000 years ago.
New evidence suggests another group may also have been extant as recently as 11,500 years ago, the Red Deer Cave people of China. Chris Stringer of the Natural History Museum in London has suggested that these people could be a result of mating between Denisovans and modern humans. Other scientists remain skeptical, suggesting that the unique features are within the variations expected for human populations.
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