BAR HARBOR — Nearly all American Indians are descendants of a single small band of pioneers who walked across what’s now the Bering Strait from Asia 15,000 to 30,000 years ago, a genetics researcher said Thursday.

The descendants of this hardy group make up 95 percent of American Indians, including the Mayans, Incas and many other 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 the genes that are related to the body’s energy production. The genes were extracted from blood samples from members of three different Indian groups.

In a presentation during a genetics course at the Jackson Laboratory in Bar Harbor, Wallace also reported using the same energy-producing genes — called mitochondria — to identify for the first time the cause of a form of epilepsy.

The mitochondrial genes, which are separate from the body’s other genes, are passed on to children only by mothers, not by fathers.

Studies of the genes allow researchers to trace maternal ancestry, Wallace explained.

The research on 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 significantly extends the conclusions about Indian origins that can be made using language studies.

In March, anthropologists met in Boulder, Colo., to debate a suggestion by Joseph Greenberg of Stanford University that most American Indian languages derived from one ancestral language.

That controversial view is supported by Wallace’s studies, which trace most American Indians to the migration of a single small group of people who presumably spoke the same language, Wallace said.

Other researchers have identified up to 200 linguistic groups, said Greenberg. That would suggest there had been many separate migrations or that the migrations occurred so long ago that the original language had had time to split into many different forms.

Wallace said his data argues strongly against those possibilities.

Wallace is trying to determine when the small group of Indian pioneers lived. The land bridge across the Bering Strait existed from about 30,000 years ago, when the glaciers that covered it receded, until about 15,000 years ago, when the glaciers melted and water covered the bridge.

He hopes to establish the time of migration using techniques to find how much time it took for the ancestors’ genes to diversify to the way they are among Indians today.

The studies might also be used to test the longshot theory that American Indians descended from Polynesians who managed to migrate from their islands in the south and central Pacific.