Scientists use DNA fragments to trace the migration of mod...( Human beings may have made their first ...)

Human beings may have made their first journey out of Africa as recently as 70,000 years ago, according to a new study by geneticists from Stanford University and the Russian Academy of Sciences. Writing in the American Journal of Human Genetics, the researchers estimate that the entire population of ancestral humans at the time of the African expansion consisted of only about 2,000 individuals.

"This estimate does not preclude the presence of other populations of Homo sapiens sapiens [modern humans] in Africa, although it suggests that they were probably isolated from one another genetically, and that contemporary worldwide populations descend from one or very few of those populations," said Marcus W. Feldman, the Burnet C. and Mildred Finley Wohlford Professor at Stanford and co-author of the study.

The small size of our ancestral population may explain why there is so little genetic variability in human DNA compared with that of chimpanzees and other closely related species, Feldman added.

The study, published in the May edition of the journal, is based on research conducted in Feldman`s Stanford laboratory in collaboration with co-authors Lev A. Zhivotovsky of the Russian Academy and former Stanford graduate student Noah A. Rosenberg, now at the University of Southern California.

"Our results are consistent with the `out-of-Africa` theory, according to which a sub-Saharan African ancestral population gave rise to all populations of anatomically modern humans through a chain of migrations to the Middle East, Europe, Asia, Oceania and America," Feldman noted.

Ancient roots

Since all human beings have virtually identical DNA, geneticists have to look for slight chemical variations that distinguish one population from another. One technique involves the use of "microsatellites" - short repetitive fragments of DNA whose patterns of variation differ among populations. Because microsatellites are passed from genera
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
27-May-2003

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