BAR HARBOR, MAINE, JULY 26 -- Nearly all American Indians are descendants of a single small band of pioneers who crossed into the New World from Asia perhaps 15,000 to 30,000 years ago, a genetics researcher said today.

The descendants of this hardy group make up 95 percent of American Indians, including the Mayas, Incas and many others spread throughout North, Central and South America. The exceptions are the Eskimos and Aleuts of the Arctic rim, the Navajos, Apaches and a few others who arrived later, said Douglas Wallace of Emory University in Atlanta.

"It was clearly a small migration," Wallace said of the ancestral group. He based his findings on studies of special sets of genes found outside the nuclei of cells.

The genes are in the cell's energy-processing structures called mitochondria. They are passed on to children by mothers, not by fathers. Studies of the genes allow researchers to trace maternal ancestry, Wallace explained during a meeting at the Jackson Laboratory here. These are the same genes that were used a few years ago to suggest that all modern humans descended from one African woman -- immediately dubbed Eve -- who lived about 200,000 years ago.

Analysis of mitochondrial DNA from American Indians showed that the vast majority descended from four women in that original migrating group.

"That's a striking finding," said Michael Silverstein, an anthropologist at the University of Chicago who studies American Indian languages.

If the finding is confirmed, Silverstein said, it would support a theory that all American Indian languages are descendants of one ancestral tongue. Anthropologists have been debating such a suggestion by Joseph Greenberg of Stanford University.

Wallace hopes to establish the time of migration using techniques to find how long it took for ancestors' genes to diversify through mutation to produce the differences found among Indians today.