Archaeo-Chemists Track Ancient DNA
THE molecule that carries the genetic blueprints of plants, animals, and humans - DNA - has opened a new window into the past. Its ability to reflect both differences and linkages between individuals and families, as well as between larger groups, is the key to a fast-growing science of biomolecular archaeology that would have seemed a science fiction dream even a decade ago.
In one of the latest developments, Peter Parham and David A. Lawlor at Stanford University in Palo Alto, Calif., and William W. Hauswirth and Cynthia D. Dickel at the University of Florida at Gainsville have studied DNA from the nuclei of cells in human brain tissue. It is preserved at what is known as the Windover site - a swampy pond in central Florida. Remains of 165 individuals in the pond are 6,990 to 8,130 years old.
As the archaeo-chemists explain in describing their research recently in Science, they have just begun to study distinctive features in such DNA. They say that further work "may determine familial relationships between Windover individuals and further define the relationship between this ancient population and modern Amerindian populations."
That would supplement a 1989 study by Swedish biochemist Svante Paabo. While doing postdoctoral work at the University of California, Berkeley, Dr. Paabo extracted DNA from a 7,000-year-old human brain preserved in another Florida bog called Little Salt Spring. This raised a question about the first migrations of Amerindians from Asia. Modern Amerindians show only three distinct DNA lineages. Paabo found indications of a fourth lineage. Such studies may eventually show approximately where in Asia the or iginal migrating groups came from and how many people were in each group.
This is different from the DNA "fingerprinting" used to link criminals with their crimes. Ancient DNA is hard to work with. It's scarce and generally is damaged. The technical breakthrough that makes the new molecular archaeology possible was developed six years ago at Cetus Corporation in San Francisco. Called by a name that only a chemist would love - polymerase chain reaction - it enables a researcher to pick out a desired DNA segment even when the sample is small and damaged. It then makes hundreds of thousands of copies of that segment to produce enough material for standard analyses.
Until now, researchers such as Paabo have worked with DNA from mitochondria. These units, which are employed in energy production within a living cell, lie outside the cell nucleus. They have limited genetic information and are inherited only from mothers. DNA in the nucleus has much more genetic information and is inherited from both parents. But it is very scarce. Now Parham and his colleagues have learned to work with nuclear DNA, opening up a potentially rich research field.
This kind of work has implications beyond archaeology. The hundreds of millions of dead and dried specimens in museums potentially are a rich store of DNA that biologists could use to trace evolution of both extinct and living species.
Thus a technical breakthrough in one field - in this case DNA chemistry - can open new research avenues in other fields. As Paabo has noted, the new techniques "have enabled us to ... catch evolution red-handed."