ROANOKE TIMES
Copyright (c) 1995, Roanoke Times
DATE: Monday, December 25, 1995 TAG: 9512260040
SECTION: NATIONAL/INTERNATIONAL PAGE: C-9 EDITION: HOLIDAY
DATELINE: IRVINE, CALIF.
SOURCE: PAT BRENNAN ORANGE COUNTY REGISTER
THE LATEST SCIENTIFIC theories say African Eve is not a woman, but a molecule.
One of the most stirring images in the debate over humanity's beginnings is that of ``African Eve,'' the genetic mother of us all who lived about 200,000 years ago.
But an evolutionary biologist at the University of California, Irvine, says the cherished image is a myth.
``What my work does, largely, is to prove that we could not have had fewer than 100,000 ancestors at any one time,'' said Professor Francisco Ayala, whose findings were published Friday in the journal Science.
Put another way, African Eve is not a woman. She's a molecule.
To understand this notion, we must step into the wild, uncharted country known as paleoanthropology - the study of the bone fragments, fossil tools, heaps of refuse and scratches in the dirt left by long-dead humans. And near-humans.
Few fields of inquiry have inspired so much public conflict, intramural bile and poison-pen diatribes among normally civilized scientists.
And the furious debate has been energized in recent years by DNA researchers, who discovered that within our cells are tiny molecular ``clocks'' - bits of flotsam that change, or mutate, at a predictable rate over millions of years.
These have been used to make solid links to our apish past and to shatter some beliefs held by scientists who prefer to draw their conclusions from skulls and teeth, not clues encrypted in strands of DNA.
The ``African Eve'' hypothesis, which first captured the public imagination in 1987, is perhaps the most stunning application of this new technology. Researchers led by the late Allan C. Wilson of the University of California, Berkeley, focused their attention on microscopic energy factories, known as mitochondria, that enjoy a quasi-independent lifestyle as they perform chores inside our cells.
These organelles evolve separately from the DNA in the nucleus of human cells; they possess their own sets of DNA and their own rates of mutation. And because they are supplied exclusively by mothers to the embryos growing within them, they are passed on from generation to generation only by women.
By measuring the rate of change in the mitochondrial DNA, and extrapolating backward in time, the Wilson team effectively clocked the origin of human mitochondria.
They pegged it to 200,000 years ago, on the African continent. And they confidently sketched the enduring image of Eve - the prime ancestor of our species, homo sapiens.
But in a paper likely to ignite controversy, Ayala contends that science popularizers - and some scientists - who promote the African Eve idea are making a fundamental error.
``The mitochondrial Eve hypothesis emanates from a confusion between gene genealogies and individual genealogies,'' Ayala writes in the introduction to his paper.
Famed in scientific circles for his work on the genealogy of fruit flies, Ayala uses his own venerable genealogy to illustrate his point.
``[My] name was created in the year 1085, when the king of Spain, Alfonso the Sixth, granted to a particular vassal the land of Ayala,'' he said. ``All Ayalas who live in the world today - in Spain, Mexico, the Philippines - all descend from that particular man.''
That makes the original Ayala ``the ancestor of all of us,'' he said. But it would be a mistake to assume that the first Ayala to hold the name originated all the DNA in the bodies of today's Ayalas.
In the same way, the originator of today's mitochondrial DNA - the hypothesized African Eve - also cannot be the originator of all human DNA.
Genes come from many different ancestors, not one, or even a few, Ayala said. Mitochondrial DNA represents only 1/400,000th of the DNA in our bodies.
``Think of an inheritance - $4 million dollars,'' Ayala said. ``Ten dollars comes from an aunt somewhere in Africa 200,000 years ago. But you are more interested in the rest of the $4 million, which comes from different places.''
Another professor of human genetics, Luigi Luca Cavalli-Sforza of Stanford University, said he drew a similar conclusion from gene studies of his own 10 years ago. He said few scientists still believe in an African Eve.
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