The geneticists working on the Y chromosome may eventually be able to date migrations with similar precision. The major class of mutation on the Y is so rare that the ticks of the mutation clock are too many thousands of years apart to be reliably averaged. But a second kind of mutation occurs more rapidly and the combination of the two may make a reasonable clock.
Analysis of the Y chromosome has already yielded interesting results. Dr. Ariella Oppenheim of the Hebrew University in Jerusalem said she had found considerable similarity between Jews and Israeli and Palestinian Arabs, as if the Y chromosomes of both groups had been drawn from a common population that began to expand 7,800 years ago.
In the middle ages, the Vikings settled in Greenland but contact with their colonies was lost at the beginning of the 15th century. In 1720, by which time the Danes had long become Protestants, there arose considerable concern that the missing colonists, if they still existed, would be Roman Catholics and in need of conversion. An expedition was sent to Greenland but found only ruined houses and Eskimos. Did the Vikings perish or intermarry? An analysis of Greenlanders' mitochondrial DNA shows only genetic signatures typical of the New World, and it indicates their unalloyed descent from Eskimos of Alaska. "It looks bad for the Vikings," said Dr. Peter Forster of the University of Cambridge, a co- author of the study.
Dr. Douglas Wallace of Emory University, who pioneered the use of mitochondrial DNA to analyze human origins, said of the emerging type of analysis: "The Y chromosome has a great future. But it is a very new technology."