Fossils showing specific characteristics deemed to be transitional between Homo erectus and Homo sapiens are grouped in the category of archaic humans and referred to as archaic Homo sapiens, or as Homo heidelbergensis and Homo neanderthalensis.
The earliest fossils displaying the morphological characteristics associated with early archaic humans, or Homo heidelbergensis, are found in eastern Africa and date to about 600,000 years ago. Similar fossils are found in Eurasia at Mauer, Germany, by about 500,000 years ago; at Atapuerca, Spain, by 300,000 years ago; and at Dali, China, by 200,000 to 300,000 years ago. It is unclear whether archaic humans occurred in Southeast Asia.
Fossils found in western Eurasia, dating to between about 200,000 and 30,000 years ago, and characterized by specific morphological characteristics, are referred to as late archaic humans (Homo sapiens) or Neanderthals (Homo neanderthalensis).
Archaic human sites in the late Pleistocene reveal evidence of increased tool complexity, increased hunting efficiency, social cooperation, burials, and possibly the practice of postmortem modification of bodies.
The earliest fossils characterized as anatomically modern humans (Homo sapiens sapiens or Home sapiens idaltu) are found in eastern Africa and date to about 160,000 years ago. Subsequent finds of similar fossils occur in southern Africa dating to 130,000 years ago and in the Middle East dating to 110,000 years ago. Thereafter the fossils defined as modern humans show up at sites in China by 70,000 years ago, Australia by 60,000 years ago, western Europe by 40,000 years ago, and the Americas by at least 15,000 years ago.
Material culture associated with modern human sites is increasingly complex relative to archaic forms. These complexities include blade tools, dramatic increases in the types of tools, ubiquitous burials, some postmortem modification of bodies, and use of symbols and art. By 20,000 years ago the first hints of modern human sedentariness and population patterns begin to appear.
Scientists disagree over the way in which modern humans arose. Three main models have been proposed.
The Recent African Origin (RAO) model assumes that modern humans appeared as the result of a recent speciation event in Africa and subsequently dispersed throughout the rest of the world, replacing or assimilating all archaic human populations.
The Multiregional Evolution (MRE) model assumes that Homo sapiens is an old species (originating about 1.7 million years ago) and all populations of archaic humans transitioned to modern forms due to consistent gene flow and similar adaptive trajectories.
The Multiple Dispersal (MD) model assumes three major dispersals of human populations from Africa in the last 1.7 million years, the first coinciding with the movement of H. erectus out of Africa, the second with the appearance of early archaics (or H. heidelbergensis), and the third with the appearance of anatomically modern humans. This model also predicts recurrent gene flow across all time periods.
Fossil and genetic evidence offer some support for both the RAO and MRE models. The MD model may be the best fit for current genetic data sets.
