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11.9 Models of Human Evolution

Today, all humans are classified as belonging to the species Homo sapiens. However, this is not the first species of hominids: the first species of genus Homo, Homo habilis, evolved in East Africa at least 2 Ma and members of this species populated different parts of Africa in a relatively short time. Homo erectus evolved more than 1.8 Ma, and by 1.5 Ma had spread throughout the Old World. Virtually all physical anthropologists agree that Homo sapiens evolved out of Homo erectus. Anthropologists have been divided as to whether Homo sapiens evolved as one interconnected species from Homo erectus (called the Multiregional Model, or the Regional Continuity Model), or evolved only in East Africa, and then migrated out of Africa and replaced Homo erectus populations throughout the Old World (called the Out of Africa Model or the Complete Replacement Model). Anthropologists continue to debate both possibilities, but most anthropologists currently favour the Out of Africa model.

11.9.1 Multiregional model

Advocates of the Multiregional model have argued that the simultaneous evolution of Homo sapiens in different parts of Europe and Asia would have been possible if there was a degree of gene flow between archaic populations. Similarities of morphological features between archaic European and Chinese populations and modern Homo sapiens from the same regions support a regional continuity only possible within the Multiregional model.

11.9.2 Out of Africa model

According to the “Out of Africa Model”, modern Homo sapiens evolved in Africa 200,000 years ago. Homo sapiens began migrating from Africa between 70,000 and 50,000 years ago and would eventually replace existing hominid species in Europe and Asia. The “Out of Africa Model” has gained support by recent research using mitochondrial DNA (mtDNA). After analysing genealogy trees constructed using 133 types of mtDNA, they concluded that all were descended from a woman from Africa, dubbed Mitochondrial Eve.

There are differing theories on whether there was a single exodus, or several (a Multiple Dispersal Model). There was a coastal dispersal of modern humans from the Horn of Africa around 70,000 years ago. This group helped to populate Southeast Asia and Oceania. A second wave of humans dispersed across the Sinai peninsula into Asia, resulting in the bulk of human population for Eurasia. This second group possessed a more sophisticated tool technology and was less dependent on coastal food sources than the original group. Much of the evidence for the first group’s expansion would have been destroyed by the rising sea levels at the end of the Holocene era. The multiple dispersals models is contradicted by studies indicating that the populations of Eurasia and the populations of Southeast Asia and Oceania are all descended from the same mitochondrial DNA lineages. The study further indicates that there was most likely only one single migration out of Africa that gave rise to all Non-African populations.

11.9.3 Comparison of the two models

The two models differ widely. The “Multiregional Model” suggests that the fossil record should show the same regional differences in anatomical characteristics that are currently visible today. Racial differences would be deep-rooted, going back as much as two million years. In the “Out of Africa Model”, however, the fossil record would not be expected to show continuity of anatomical characteristics over time; on the contrary, the regional characteristics of older fossils would likely be replaced globally by more modern African ones. Racial differences would be shallow-rooted, having evolved over a relatively short period of time.