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Discoveries Breathe New Life into Human Origins Debate
Nariokotome Boy, or Turkana Boy, a Homo erectus found by
Alan Walker and Richard Leakey, Lake Turkana, Kenya is the most complete
Homo erectus ever found.
Where did humans come from? With the help of modern science, this deceptively simple question has brought about myriad debates regarding the origin of modern humanity. The two strongest origin theories seem incompatible, yet each continues to return evidence backing their own theory.
Theres always alternative explanations [to new evidence], said John Relethford, a professor of anthropology at the State University of New York at Oneonta. It gets really confusing and complicated.
On one side: scientists who claim modern humans arose from a single cradle of civilization in Africa. On the other: those who say modern humans evolved everywhere, as populations mixed and advantageous genes spread.
The most recent discoveries fall on the side of those who argue the latter. The two studies, published separately by Australian and U.S. scientists, examine two types of evidence: DNA and anatomical. Both studies, say the scientists, show that modern humans could not have evolved from a single African source.
SEARCHING FOR THE FIRST HOMO SAPIENS
Neither side disputes that hominids once emerged from Africa, colonizing Eurasia.
One circle of scientists maintains that human precursors remaining in Africa evolved into a second Out of Africa group of physically and intellectually modern humansHomo sapienswho recolonized Eurasia, replacing so-called archaic humans.
The theory maintains that Neandertals and other geographically distinct hominidsdescendents of the first African exodusbecame extinct with the arrival of modern humans 100,000 years ago.
One version of the Out of Africa theory holds that modern humans can be traced back to a single African ancestor, dubbed Eve.
Opposition to this theory comes from multiregionalists, anthropologists who see modern man arising from a process of change within a species, said one of the theorys architects, Milford Wolpoff.
Multiregionalists see modern humans arising from these changes in Africa, Eurasia, and Australia. The species that evolved, they say, gained traits held by all modern humans but remained racially diverse because of geographical adaptations and the distances between populations.
The modern traits were shared species-wide through interbreeding, maintains Wolpoff.
The [Homo sapiens] genes spread widely and were successful, he explained.
Wolpoff also argues for a much earlier date for the evolution of Homo sapiens than Out of Africa theorists postulate.
Theres only been one species for a long time, he said.
NEW FINDINGS SUGGEST NO EVE
The findings of two of multiregionalisms architects, Wolpoff and Australian National Universitys Alan Thorne, lend credence to their theory.
Wolpoffs team of scientists compared the anatomical structure of bones found in Australia and central Europe, looking for signs of a uniquely African ancestry. They found none. Their report, published in Science, reveals that Wolpoff found evidence of both African and local ancestors.
We could not disprove the hypothesis of multiple ancestry, he said. We dont think [the replacement theory] could be correct.
Meanwhile Thorne and other Australian researchers were studying the DNA of Australian skeletons, including Mungo Man, a modern human skeleton that has been dated as far back as 60,000 years.
What the Australian team found, said Wolpoff, was that the oldest of the Australian skeletons does not have African mitochondrial DNA.
Their research, published in the Proceedings of the National Academy of Sciences, suggests that, anatomically modern humans were present in Australia before the complete fixation of mtDNA now found in all living people.
Despite this new evidence, the debate about the origins of modern humans is likely to continue, said Relethford. I dont think any one single study is going to do it.
A lot of people argue for an intermediate ground, he added, [that] the change to modern humans did take place first in Africa and then spread out, but did not completely replace archaic human populations.
Wolpoff, however, contends that once a new generation of scientists examines the issue, they will back multiregionalism.
Were writing this for them, he said.