The "Out of Africa" theory of human migration proposes that our ancient Homo sapiens ancestors evolved in Africa before migrating in a single wave to the Asian continent about 60,000 years ago. Studies made over the past 15 years, however, raise questions on the theory.
Out Of Africa Migration Model In Need Of Revision
A new study, which was published in the journal Science on Dec. 8, suggests that new discoveries made over recent years show that modern humans may have originated from several migrations from Africa, which started as early as 120,000 years ago, or 60,000 years earlier than previous estimates. Researchers, for instance, have found Homo sapien specimens in China, Southeast Asia, and even Australia that were dated between 70,000 and 120,000 years ago.
Early Migrants Were Possibly A Group Of Foragers
Study researcher Michael Petraglia, from Max Planck Institute for the Science of Human History, said that the early migrants were possibly a small group of foragers and that the later, major "out of Africa" event most likely happened about 60,000 years ago.
"The traditional 'out of Africa' model, which posits a dispersal of modern Homo sapiens across Eurasia as a single wave at ~60,000 years ago and the subsequent replacement of all indigenous populations, is in need of revision," the researchers wrote in their study. "Important findings highlighted here include growing evidence for multiple dispersals predating 60,000 years ago in regions such as southern and eastern Asia."
Interbreeding Among Ancient Human Species
The modern humans that moved into Asia met other species, which include the mid-Pleistocene Homo, the Denisovans, Neanderthals, and possibly the H. floresiensis.
Hereditary investigations revealed that some degree of inbreeding occurred during these interactions, which scientists said has led to some beneficial traits in modern humans such as having a strong immune system. The Melanesians were found to be part Denisovan. Non-Africans likewise carry at least 1 to 4 percent Neanderthal DNA in their genes.
It was previously thought that the interbreeding happened after the "Out of Africa" migration but a 2016 study showed that the early modern humans, who originated from Africa and Neanderthals, had lived outside of the continent interbred earlier than previously thought.
"Interbreeding between several archaic Homo sapiens populations certainly occurred in Africa," said Christopher Bae of the University of Hawaii at Manoa.
"This greater biogenetic diversity in Africa has long been recognized part of the argument to consider Africa as having a longer history for contemporary humans than Asia."