New Analysis Shows Three Human Migrations Out Of Africa
February 10, 2006
Source: Washington University in St. Louis
A new, more robust analysis of recently derived human gene
trees by Alan R.
Templeton, Ph.D, of Washington University in St Louis, shows three distinct
major waves of human migration out of Africa instead of just two, and
statistically refutes - strongly - the 'Out of Africa' replacement theory.
That theory holds that populations of Homo sapiens left Africa 100,000 years
ago and wiped out existing populations of humans. Templeton has shown that
the African populations interbred with the Eurasian populations - thus,
making love, not war.
"The 'Out of Africa' replacement theory has always been a big controversy,"
Templeton said. "I set up a null hypothesis and the program rejected that
hypothesis using the new data with a probability level of 10 to the minus
17th. In science, you don't get any more conclusive than that. It says that
the hypothesis of no interbreeding is so grossly incompatible with the data,
that you can reject it."
Templeton's analysis is considered to be the only definitive statistical
test to refute the theory, dominant in human evolution science for more than
"Not only does the new analysis reject the theory, it demolishes it,"
Templeton published his results in the Yearbook of Physical Anthropology,
A trellis, not a tree
He used a computer program called GEODIS, which he created in 1995 and later
modified with the help of David Posada, Ph.D., and Keith Crandall, Ph.D. at
Brigham Young University, to determine genetic relationships among and
within populations based on an examination of specific haplotypes, clusters
of genes that are inherited as a unit.
In 2002, Templeton analyzed ten different haplotype trees and performed
phylogeographic analyses that reconstructed the history of the species
through space and time.
Three years later, he had 25 regions to analyze and the data provided
molecular evidence of a third migration, this one the oldest, back to 1.9
million years ago.
"This time frame corresponds extremely well with the fossil record, which
shows Homo erectus expanding out of Africa then," Templeton said.
Another novel find is that populations of Homo erectus in Eurasia had
recurrent genetic interchange with African populations 1.5 million years
ago, much earlier than previously thought, and that these populations
persisted instead of going extinct, which some human evolution researchers
thought had occurred.
The new data confirm an expansion out of Africa to 700,000 years ago that
was detected in the 2002 analysis.
"Both (the 1.9 million and 700,000 year) expansions coincide with recent
paleoclimatic data that indicate periods of very high rainfall in eastern
Africa, making what is now the Sahara Desert a savannah," Templeton said.
"That makes the timing very amenable for movements of large populations
through the area."
Templeton said that the fossil record indicates a significant change in
brain size for modern humans at 700,000 years ago as well as the adaptation
and expansion of a new stone tool culture first found in Africa and later at
700,000 years expanded throughout Eurasia.
"By the time you're done with this phase you can be 99 percent confident
that there was recurrent genetic interchange between African and Eurasian
populations," he said. "So the idea of pure, distinct races in humans does
not exist. We humans don't have a tree relationship, rather a trellis. We're
Editor's Note: The original news release can be found here.