Common origin cited for American Indians.

Common origin cited for American Indians 

The vast majority of American Indians most likely descended from a single migrating population from Asia, biochemist Douglas C. Wallace told a scientific gathering last week in Bar Harbor, Maine.

With that assertion, Wallace enters the long-running debate over who first settled in the New World. Much recent attention has focused on the linguistic research of Stanford University's Joseph Greenberg, who argues that Native American languages fall into three groups that descended from one ancestral tongue (SN: 6/9/90, p.360).

"Our findings support Greenberg's hypothesis," Wallace told SCIENCE NEWS. "If we go back far enough in time, most American Indians should genetically link up with one Asian population."

Wallace and his co-workers at Emory University in Atlanta studied mitochondrial DNA from South America's Ticuna Indians, Central America's Maya and North America's Pima. A total of 99 individuals, each with a different maternal ancestry, donated blood for genetic analysis.

Mitochondrial genes lie outside the nuclei of cells and are inherited only from the mother. Using DNA-cutting enzymes to snip mitochondrial samples at specific locations, the researchers pinpointed chemical sequences at those locations.

All three tribes have high frequencies of mitochondrial DNA containing at least three of four rare chemical sequences, two of which otherwise occur only in Asian populations, Wallace reports. Early Asian immigrants to the New World must have carried the four "master" sequences with them, he maintains. Moreover, most modern American Indians apparently descended from at least four women in an early migrating group, he adds.

Mitochondrial analysis has not yet yielded an entry date for the prehistoric settlers, although Wallace estimates that Asians first trekked into the Americas 15,000 to 30,000 years ago. Exceptions to the shared mitochondrial heritage include Eskimos, Aleuts, Navajos, Apaches and a few others who arrived later on, he says.

Wallace reported these results, detailed in the March AMERICAN JOURNAL OF HUMAN GENETICS, at last week's Short Course in Medical and Experimental Mammalian Genetics.

His group's findings contrast with those of another genetic study reported in March (SN: 6/9/90, p.361). Indians from predominantly Pacific Northwest tribes encompass up to 30 mitochondrial DNA lineages extending back 40,000 to 50,000 years, asserted a team led by Svante Paabo of the University of California, Berkeley. A series of separate migrations must have fueled the observed genetic diversity, Paabo proposed.

Paabo and his colleagues studied chemical substitutions in a small section of mitochondrial DNA known to undergo rapid structural changes; Wallace's team searched for genetic markers along the entire thread of mitochondrial DNA.

Wallace says he has not seen Paabo's data and does not know why the two studies arrive at opposite conclusions. However, he says the tribes he studied were largely free of the outside genetic influences that would obscure ancient mitochondrial mothers. Analysis of blood types and proteins affirms that the Ticuna and Pima tribes in his study had virtually no genes from non-native groups, while the Maya tribe possessed a small amount of European ancestry.