No crossbreeding with NeanderthalsNo hanky spanky with the Neanderthals, or ape-men (Homo erectus) in our family tree. A new study shows that we are 100 % an African product. This is the result of a comparison of skulls and DNA of human remains found worldwide. It appears that human species living elsewhere in the world did not contribute to our ancestry.
The team led by Andrea Manica at the University of Cambridge, England, compared over 6,000 skulls from more than 100 ancient human populations. The research discovered a loss of genetic diversity the farther away from Africa people lived.
This supports the single origin, or "out of Africa" theory that states early humans colonized the Earth after spreading out of Africa some 80,000 years ago.
The opposite is the "multiregional" theory that states Homo sapiens emerged from various human populations in different areas of the world.
"The origin of anatomically modern humans has been the focus of much-heated debate. We have combined our genetic data with new measurements of a large sample of skulls to show definitively that modern humans originated from a single area." said Manica.
Other researches showed that genetic differences in human populations correlate with distance from Africa.
In the new approach, the researchers measured 37 traits in male and female skulls of at most 2,000 years old, as these were better preserved. Environment was found to influence many human skull traits. Distance from Africa determined up to 25 % of variation in the skulls' traits.
"The researchers made sure that the DNA analysis used the same framework as the analysis for the skulls-so the two could be fully compared. I would argue we had two independent shots at getting the same answer, and remarkably, the answer is exactly the same," said Manica.
The lowest genetic variation level was discovered in ancient populations from South America and Australia, the most remote inhabited areas from Africa. This situation sustains the idea that Homo sapiens arose solely in Africa. Modern human populations built up genetic and physical diversity for about 150,000 years before spreading out of Africa, but about 20,000 and 30,000 years ago they reached Australia and about 12,000 years ago South America.
"The more you move away from that center of diversity where you started, the less diversity you have," Manica said.
This pattern matched globally and the authors place the origins of modern humans in south-central Africa.
Other theories give at least partially a non-African origin to Homo sapiens, from descendants of Homo habilis, which spread out of Africa at least 1.5 million years ago. These are the Neanderthals of Europe and western Asia and the ape-man (Homo erectus) of eastern/southeastern Asia and even the controversial hobbits from the Indonesian island of Flores.
"What we can confidently say is that there has not been a wave [of anatomically modern humans] starting from somewhere else, because then you'd find a second area with more variability. Matings with the Neandertals never ever happened, but if it did happen, none of the descendants stayed around. Effectively, any mating had no contribution whatsoever to modern humans," Manica said.
This challenges the findings of the anthropologist Erik Trinkhaus of Washington University in St. Louis, Missouri, who discovered fossil evidence pointing that Homo sapiens and Neandertals did interbreed.
"The idea that humans get more uniform further from Africa is simply ludicrous. Modern-day Chinese and Australian Aborigines look no more similar to each other than do Africans and Europeans." said Trinkhaus.
Still, this affirmation has something ludicrous, as Manica's team explains diversity inside a given population, not amongst populations.
Still, there are some researchers that insist that even if Homo sapiens emerged in Africa, it absorbed local archaic populations.
"It could very well be that there was a recent out-of-Africa expansion, coupled with some either small or large amount of genetic exchange with humans outside of Africa," said Charles Roseman, of the University of Illinois at Urbana-Champaign.