New gene study enters Indo-European fray.

Analysis of DNA from modern humans supports other indications that a northward migration of farmers from ancient Turkey and the Middle East, beginning around 9,000 years ago, shaped Europe's genetic geography. The DNA data also bolster a controversial theory that links this agricultural expansion to the spread of Indo-European languages, contend Alberto Piazza, a geneticist at the University of Torino, Italy, and his colleagues.

However, the genetic finds may also lend weight to a contrary proposal, the researchers add: that nomads from the central Eurasian Yamna culture spread Indo-European languages shortly after they invented wheeled vehicles approximately 5,500 years ago (SN: 2/25/95, p.120).

"It is possible that both expansions were responsible for the spread of different subfamilies of Indo-European languages, but our genetic data cannot resolve their relative importance," the researchers conclude in the June 20 Proceedings of the National Academy of Sciences.

Their investigation employs blood samples gathered earlier as part of an analysis of worldwide human genetic variation. Study coauthor L. Luca Cavalli-Sforza, a geneticist at Stanford University, directed the international project. Cavalli-Sforza and his colleagues describe those findings in The History and Geography of Human Genes (1994, Princeton University Press).

Piazza's team analyzed DNA from people in Europe and adjacent parts of central Eurasia and the Middle East. The researchers calculated the frequency of certain structural variations in 95 genes. They then used a statistical procedure to sort through the catalog of measured genetic differences, looking for geographic patterns of variation.

From about one-quarter of the measured genetic differences they extracted a pattern of numerous DNA changes in Turkey and the Middle East, with genetic mutations gradually declining in northern locales. Since such changes accumulate over time, early farmers moving north and settling the European continent probably left this genetic legacy, the scientists argue.

This pattern of DNA changes also appears to jibe with the theory that farmers moving northward from ancient Turkey spread Indo-European languages, Piazza's team holds.

A map developed from about one-fifth of the observed gene differences shows a trend toward a genetic split between populations in the extreme north and those in southern regions. The researchers suggest that this split may have two causes. It could result from differing adaptations to cold climates as well as the separation of northern groups, which spoke Uralic languages, from Indo-European speakers.

A third map, derived from about one-tenth of the entire set of gene differences, displays DNA changes that peak in central Eurasia and tail off throughout Europe. This pattern corresponds roughly to the movement of Yamna people into Europe.

Despite the new findings, controversy over Indo-European origins seems unlikely to diminish anytime soon. Available genetic data cannot untangle the roots of Indo-European languages, asserts Robert R. Sokal, a biostatistician at the State University of New York at Stony Brook.

However, the new evidence corroborates earlier genetic studies that found traces of an expansion of early farmers from Turkey into Europe, according to Sokal (SN: 8/22/92, p.117).

A study directed by Sokal, slated to appear later this year in Human Biology, finds no linguistic evidence of an Indo-European origin in ancient Turkey. His team examined geographic patterns in the number of related words in known Indo-European languages.

"At this point, I can't substantiate any hypothesis of Indo-European origins," Sokal remarks.