NEW YORK -- A new genetic study has indicated that every person in the world is descended from a single woman who lived in Africa 200,000 years ago, scientists reported Wednesday.
The California biochemists, reporting in the British science journal Nature, studied cellular DNA of 147 women from around the world and made their claim based on the assumption that DNA evolves at a constant, known rate. Deoxyribonucleic acid, or DNA, holds the blueprints for heredity.
Constructing a genetic family tree that supposedly encompasses all humans, the scientists traced its roots back to a single female who they said was probably a member of the first small band of Homo sapiens who evolved in Africa about 200,000 years ago. Her descendants began migrating to Europe and Asia approximately 70,000 years later, they said.
The scientists, all researchers from the University of California at Berkeley, used women in their study because they tested the DNA of mitochondria, an energy-producing portion of a cell inherited exclusively from the mother.
The study, based on genetic information passed from mothers, could not indicate ancestral paternity, they said.
Anthropologists interviewed before the report was published criticized the findings, even though they said the Berkeley theory does not clash with fossil evidence of the earliest humans.
'I have difficulty accepting a theory that says all populations derive from one female,' said George J. Armelagos, a professor of anthropology at the University of Massachusetts at Amherst and spokesman for the American Anthropolocial Association.
'We also don't know enough about DNA rate of change,' he said. 'Their time clock could be way off.'
Using the premise that DNA evolves at a known rate, the Berkeley scientists compared the mitochondrial DNA of Africans, Asians, Caucasians and aborigines of Australia and New Guinea.
According to the report in Nature, they used the comparisons to map out a gene 'genealogy linking maternal lineages in modern human populations to a common ancestral female.'
The scientists believe the woman was African because all the DNA samples had characteristics believed to have evolved hundreds of thousands of years ago in Africa. Fossil evidence also indicates the first Homo sapiens evolved in Africa, the researchers noted in their report. They did not speculate on what may have happened to the woman's contemporaries.