With the national publication Friday of a paper by a UC Irvine evolutionary biologist, another dissenting salvo has been fired at the controversial theory that modern-day human genes can be traced back some 200,000 years to a sole genetic mother.
The latest edition of the journal Science features a seven-page paper by professor Francisco Ayala that disputes the nearly decade-old theory that one woman, or the "mitochondrial Eve," in Africa was the prime mother of modern-day humans.
"It is a romantic theory, yes, to have a mitochondrial Eve," Ayala said in an interview Friday. "It is consistent with the biblical myth and it is easier to imagine. But it is wrong, it is flawed logic."
Ayala's research shows that some genetic material locked within modern-day DNA traces back perhaps 60 million years, and that some 100,000 "Eves" existed long before the sole female cited by the earlier theory.
The mitochondrial Eve theory was devised by scientists at UC Berkeley who in the 1980s said the rate of mitochondrial DNA mutations within human cells acted as a sort of timekeeper, providing clues that pointed to the species' past.
DNA in one part of the human cell, the mitochondria, is passed down only through mothers, so tracking its mutation led the Berkeley team to a startling conclusion: A woman who lived in Africa 200,000 years ago was the source of the genes that exist in all humans today.
But that theory has been the target of a steady barrage of criticism and skepticism, the latest from Ayala.
Ayala said the Berkeley research confused gene genealogies with the genealogy of people. The Eve they found may indeed have been the starting point of the mitochondrial DNA that still survives, but contributors of other genetic attributes existed before her and at the same time.
Ayala's research also counters the belief by some scientists that there were "bottle-necks," large drops in the early human population that made it easier for evolutionary changes to grab hold.
The suggestion that the differentiation between races was a fairly recent splinter growth in the evolution of humans has often accompanied the mitochondrial Eve theory. Ayala also disputes that, suggesting in his journal paper that the race differences began about 1.8 million years ago, when human growth took the species outward from Africa.
Ayala, a 61-year-old native of Spain, is chairman of the board of directors for the American Assn. for the Advancement of Science, an organization with a membership of 140,000 scientists. He is the Donald Bren Professor of Biological Sciences at UCI.