A new analysis of DNA
evidence offers a new twist on the popular "Out of Africa" theory
of human origins: Modern humans interbred with other populations around
the world for hundreds of thousands of years rather than replacing them.
Among the study's
implications: the genes of people today carry vestiges of genes of Neanderthals
and other extinct branches of the human family. According to the original
Out of Africa theory, ancestors to today's human population migrated from
Africa 100,000 years ago, and they replaced less modern populations in
Europe and Asia.
The new study by population
biologist Alan R. Templeton of Washington University in St. Louis suggests
instead that there were at least two distinct migrations. The first wave
occurred between 420,000 and 840,000 years ago, he said, and the second
between 80,000 and 150,000 years ago.According to Templeton,
the most recent migration, and perhaps both, were not "replacement
he said DNA evidence shows evidence of interbreeding.
appears in this week's Nature journal. While the study offers no original
data, it employs a unique statistical method that Templeton argues more
reliably traces genetic trails over time. Templeton was lecturing in Israel
and unavailable for comment. Other scientists said Templeton's conclusions
could reconcile the Out of Africa theory with fossil evidence that suggests
there was more than one migration wave. But they were less sure that Templeton's
analytical model is entirely accurate.
In a separate review
in Nature, Rebecca L. Cann, a molecular biologist at the University of
Hawaii, suggested Templeton was "overambitious in the scale of his
analysis" and perhaps too eager to contribute to the contentious
For his study, Templeton developed a computer program
called GEODIS to analyze genetic material taken from thousands of present-day
humans around the world.
analyzes DNA from 10 locations in each genetic sample. Previous statistical
models that have targeted just one region of DNA _for example mitochondrial
DNA that is passed from the mother to subsequent generations.
approach has resulted in incomplete results "with low statistical
resolution," he argued.
In her rebuttal, Cann
said the new model needs to be independently verified, and its conclusions
compared to existing evidence on human origins from archaeology, linguistics
and other scientific disciplines.
"Perhaps we will
need a demonstration that GEODIS reveals the composite picture before
we can settle on how to interpret the varied signals uncovered by Templeton's
analysis on a global scale," she said.
Credit Source: Michael
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