DNA Teaches History a Few Lessons of Its Own
The New York Times "Week in Review"
May 24, 1998
HISTORY, with all its horrors, accidents and astonishments, has been interpreted as an epic tale of great men and as a tragic tale of alienated labor. It has been interpreted through the eyes of religion, psychology and metaphysics. But now the search for another kind of history is taking place.
That quest led to the exhumation of the Tomb of the Unknown Soldier this month, and to the recent disinterments of Yves Montand and Jesse James. It has drawn researchers to villages in India seeking saliva samples. Blood has been drawn from descendants of Thomas Jefferson and descendants of one of his slaves. Jews who identify themselves as descendants of the Biblical high priests have been probed.
The new history is inscribed in strands of DNA. Genetic researchers assert that there is new information that history must take into account, new evidence about once-private events, and that there are new ways of interpreting the distant human past.
Credit: Associated Press Attorney Robert
"Bob" Cooley, a descendant of former U.S.
President Thomas Jefferson, poses with a
portrait of Jefferson.
The prospect of genetic history has already heightened some anxieties over what is considered inappropriate racial analysis, while inspiring speculation about shared human origins and worldwide migrations.
On the smallest scale, the approach has become commonplace. Analysis of individual genetic fingerprints is now a standard forensic tool. DNA testing has also become crucial in paternity suits (claims of paternity led to the tests now being conducted on the remains of Montand).
The Unknown Soldier from the Vietnam War is being tested after the family of a missing Air Force lieutenant killed in 1972 argued that the Unknown might well be their relation. Since the armed forces now keep a registry of all soldiers' DNA "prints," there may never be an Unknown Soldier again.
The Thomas Jefferson case is evidence of a broader historical reach. Did Jefferson father a child with one of his slaves, Sally Hemings? That has been the oral tradition among Hemings' descendants, recently accepted as fact in the Merchant-Ivory movie "Jefferson in Paris," though dismissed by many historians. DNA testing is being used to reveal the probabilities.
But it is also being used for grander historical interpretation. In a major recent book, "The History and Geography of Human Genes"(Princeton, 1994), researchers analyzed nearly a century of genetic information from isolated communities around the world, arguing that the data reveal a path of human migrations over the past 200,000 years, beginning in Africa and extending across Asia to the Americas.
But the principal author, L. Luca Cavalli-Sforza, a professor of genetics at Stanford University, cautioned that the genetic data were too crude, including, for example, information about inherited blood type. Subtle DNA analysis was just coming into its own.
Now one kind of analysis is based on close examination of portions of the male Y chromosome, which are, remarkably, passed from father to son absolutely unchanged, providing a record of patrilineal descent unaffected by matings or migrations.
In Cavalli-Sforza's lab, a molecular biologist, Peter Underhill, and a biochemist, Peter Oefner, found ways to discern about 150 variations in that strandchanges that can only be attributed to extremely rare mutations. Identical changes in different men point to a common ancestor.
Last year, for example, Michael Hammer, a geneticist at the University of Arizona, showed that a genetic analysis of the Y chromosomes of Jewish men who ritualistically identified themselves as descendants of the Biblical High Priest Aaron and are known as Cohanim showed a high transmission of markers that were less prevalent among Jews who did not identify as Cohanim. This was evidence, Hammer said, of the accuracy of the oral tradition.
The same analysis of subtle markers has been used to assert the existence of a single prehistoric Adam, a human who had a subtle mutation in the Y chromosome whose descendants left their compatriots in Africa and populated the rest of the Earth, possibly then returning to Africa as well. Only a few living men don't have that markersome Ethiopians, Sudanese and Khoisan people in southern Africa. Analyses of DNA markers passed exclusively from mother to daughter have reached similar conclusions about a proto-Eve and her African origins.
Such markers can be valuable in discerning other historical migrations as well. The Wall Street Journal reported recently that two researchers are trying to determine whether historical accounts of ancient Jews migrating east after the destruction of their temple in the sixth century B.C. are accurate. They are testing inhabitants of villages in India, where some communities retain an oral tradition of Israelite origins.
There have also been new kinds of historical speculation and interpretation based on genetic data. Henry C. Harpending, a University of Utah anthropologist, has argued that mathematical analysis of contemporary genetic variability shows that the original human community probably had a population no larger than 10,000, at a single site. This site, he suggested in an interview, could be searched for by archaeologists.
Other researchers have made suggestions that reinterpret ancient hunter-gatherer societies. Apparently, women's genetic information has been geographically dispersed more widely than men'scontradicting the accepted evidence that men traveled more. The new hypothesis is that women encountered by men on their travels tended to return home with them, bearing children far from their birthplaces.
There is some nervousness about the genetic retelling of history, partly because, as Cavalli-Sforza points out in his book, racism has been an ancient part of historical conflict and has, in modern times, become particularly pernicious in its association with genetics. Moreover, genetic research is most fruitful within groups that have maintained long-term cohesion or isolationlike Jews, Basques, Native Americans or American blacksgroups that have characteristics associated with "race." This has led to some worry about the possible misuse of research, for example, among Jews taking part in tests about inherited disease.
But Cavalli-Sforza argues that genetic analysis of history has nothing to do with race. In fact, it proves that race is an illusion: variability within "races," he points out, is greater than genetic variability between "races."
More important, the markers now being used to trace history have no association with appearance or with known characteristics. Underhill pointed out that this is why they are so important: they have no apparent evolutionary or social value.
These markers trace events rather than help cause them. They thus seem to be the objective witnesses to history that historians have long sought, providing evidence of the most private acts of procreationnew data upon which historians are beginning to work their interpretive art.
Copyright 1998 The New York Times Company