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article imageThe Origin of Humans: South-central Africa

By Tea Lulic     Jul 19, 2007 in Science
Humans came from Africa. There were no Neanderthals or "hobbits" in human family tree. According to the new study, pattern of skull variations found around the world bolsters the "earlier species" theory.
Many have heard about "Out of Africa" theory but did not have any evidence to confirm this. Now, a study which compared the skulls from around the world and analyzed DNA of human remains says that their results point towards modern humans or Homo sapiens having a single origin in Africa.
Researchers working on this study found that variations in skulls from local populations are less diverse the farther one goes from the ancestral continent. However, they did not find any evidence that human species living elsewhere in the world actually contributed to our ancestors' make-up.
Their results confirm that humans spread out from Africa some 50,000 years ago and supplanted earlier species such as Neanderthals. Evolutionary geneticist William Amos of the University of Cambridge in England says this evidence could also pinpoint from which part of the African continent did humans flourish exactly and how messy the exodus could have been.
Research
Amos, Andrea Manica (Cambridge evolutionary bilogist) and their colleagues used approximately 4,666 male (and female?) skulls, all of which were less than 2,000 years old and collected from 105 places in the world. Since skulls varied in locations, they used 37 different measurements and compared it with the distance the population's ancestors would have had to travel to get there from Africa.
Their hypothesis was that the farther early Homo sapiens migrated from their homeland, the less variety would be seen in their skulls. All of the early humans would have carried a less diverse subset of the bigger group's genes. However, if they bred with other humans such as Neanderthals, they would have a much larger genetic variability because new genes would be injected into them and thus, boosted variability.
Furthermore, the researchers made sure that the DNA is analyzed in the same way as the skulls, so that the two could be fully compared. The lowest amount of variation was found in ancient population in South America and Australia. These two regions were the most remote from Africa.
This DNA evidence which points to low variability, researchers argue in the latest issue of Nature, could be only possible is Homo sapiens arose solely from Africa. This could be supported by the previously known evidence: populations built up genetic and physical diversity for approximately 150,000 years before migrating to other continents.
The team also noted that it was not until about 20,000-30,000 years ago that early humans reached South America and Australia.
"The more you move away from that center of diversity where you started, the less diversity you have," Manica said.
Researchers also found that this pattern was very consistent globally.
Results
The study also points out that Homo sapiens originated in south-central Africa in the "cradle of humanity."
"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," Manica said.
Manica cannot, however, say that matings with Neanderthals never ever happened and that if that did happen, none of the offspring or humans survived.
Opposing views
Anthropologist Erik Tirnkhaus of Washington University in St. Louis, Missouri, claims that he has found fossil evidence suggesting that Homo sapiens and Neanderthals did interbreed. He is skeptical about this new study and its results.
He states that the issue is about how much modern humans that were spreading out of Africa 50,000 years ago interbred with regional groups (archaic humans) and where and when did this happen. He also adds that it is ludicrous to claim that humans get more uniform further from Africa, noting that certain anatomical and genetic traits cannot be explained as simple and complete expansion of humans out of Africa.
However, Manica says that even if they did interbreed the offspring would have had different variations in their skulls. He is always open to seeing whether limited interbreeding occurred. So far, this new study and evidence found only allow for more hypotheses to be formed and tested.
Additional websites used: National Geographic
Please Note: It is not clarified whether the team studied only male skulls or male and female skulls. The sources used for this article contradict themselves.
More about Africa, Humans, Homo sapiens