OUT OF AFRICA

Out of Africa model
See also: Recent single origin hypothesis
According to the Out of Africa Model, developed by Chris Stringer and Peter Andrews, modern H. sapiens evolved in Africa 200,000 years ago. Homo sapiens began migrating from Africa between 70,000 – 50,000 years ago and would eventually replace existing hominid species in Europe and Asia.[56][57] 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.[58]
There are differing theories on whether there was a single exodus, or several (a Multiple Dispersal Model). A Multiple Dispersal Model involves the Southern Dispersal theory,[59] which has gained support in recent years from genetic, linguistic and archaeological evidence. In this theory, 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, explaining the discovery of early human sites in these areas much earlier than those in the Levant. 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.[59]. 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.[60]


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Loring Brace, an anthropologist at University of Michigan and a proponent of the idea that people descended from Neanderthals — he argues that features of skulls show a steady progression from Neanderthal to human — says the DNA evidence does not sway him. Different patterns of movement may have caused mitochrondial DNA to diverge more quickly in the past, he says. "The whole picture is still very spotty," Brace says.
Erik Trinkaus, an anthropologist at Washington University in St. Louis, says the DNA evidence does not disprove his assertion that the 25,000-year-old skeleton of child unearthed in Portugal is the descendent of a human-Neanderthal hybrid. The new research, he says, just shows interbreeding was not common.
"There is no contradiction," he says.
Goodwin also says his finding isn’t the final word. Perhaps Neanderthals and humans mated and produced sterile offspring, similar to mules, the crossbreed of horses and donkeys. "It’s very hard to prove any negative," Goodwin says. "I wouldn’t claim this to be conclusive."




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