Tracking 'Adam' And 'Eve'
Scientists on a DNA hunt through time have so far placed in time the earliest known female human ancestor and the earliest known male ancestor of a group of human beings, but the two didn't live at the same time in history.
If Adam and Eve were the ancestors of all humans alive today, as the Bible teaches, science hasn't yet gotten to the point where that can be proven.
But DNA detectives do know quite a lot, thanks to two components of the human genetic map that can be tracked back through thousands of generations of human history.
Teams of scientists from North and South America, Europe, the Mideast, Asia and the Pacific Rim tracked the Y chromosome, which is handed down only from father to son, in the DNA of over a thousand men from 22 geographic areas.
In an interview with CBS News.com, Stanford University geneticist Peter Underhill says the genetic evidence indicates that the earliest known male ancestor of all the men who were tested lived in Africa about 59,000 years ago.
Other studies tracking mitochondrial DNA, which is handed down only from mother to daughter, indicate that earliest female ancestor whose DNA shows up in the current population lived 143,000 years ago.
Geneticists come up with those dates by means of the so-called molecular clock - a mathematical method for fixing dates in history according to the rate at which DNA tends to mutate.
The mutations are, in a way, the scientist's friend.
"If there was no mutational process, all the Y chromosomes in the world and all the mitochondrial DNA in the world would be identical," says Underhill.
He points out that most DNA mutations "are harmless, in that they have no impact on the fitness of the organism, but they do create these nice molecular markers" for the long ago events which allowed the DNA to turn up in today's population.
A new study, published in the November issue of the scientific journal Nature Genetics, reconciles the two bodies of research while adding a great deal of detail to the family tree of all humans living today.
"Most of us know where our family came from, and take pride in it," says Underhill. "There is an innate curiosity within our species about our affinity with our ancestors. But our knowledge tends to go back only a few generations."
Why do we need to know the history of our DNA?
"Aside from satisfying our own scientific curiosity, and that of the public, medical geneticists who are studying traits and diseases in populations like to know why a particular group of people tends to have a higher incidence of certain traits and diseases," explains Underhill.
Scientists believe there are two main factors controlling what DNA makes it down the line to today's gene pool: natural selection, that is, survival of the fittest, and just plain chance.
A big way chance manifests itself is through the gender of one's offspring. Men who don't have sons won't be passing on their chromosome, and it will pass out of the DNA pool forever. So will the mitochondrial DNA of women who don't have daughters.
Geographic migrations also play a role.
"There is the hope," says Underhill, "that somehow all this complicated information will someday have an impact on human disease - understanding it - curing it."
He believes the research has been "a good investment" for the government, and adds that obviously a lot of businesses feel the same way, since many are putting their own dollars behind genetic research.
By Francie Grace ©2000, CBS Worldwide Inc., All Rights Reserved