Two days after a tsunami thrashed the island where his ancestors have lived for tens of thousands of years, a lone tribesman stood naked on the beach and looked up at a hovering coast guard helicopter.

The tribesman took out his bow and shot an arrow toward the rescue chopper.

It was a signal the Sentinelese have sent out to the world for millennia: They want to be left alone. Isolated from the rest of the world, the tribesmen needed to learn nature’s sights, sounds, and smells to survive.

Government officials and anthropologists believe that ancient knowledge of the movement of wind, sea, and birds may have saved the five indigenous tribes on the Indian archipelago of the Andaman and Nicobar islands from the tsunami that hit the Asian coastline December 26.

“They can smell the wind. They can gauge the depth of the sea with the sound of their oars. They have a sixth sense which we don’t possess,” said Ashish Roy, a local environmentalist and lawyer who has called on the courts to protect the tribes by preventing their contact with the outside world.

The tribes live the most ancient, nomadic lifestyle known to man, frozen in the Paleolithic past. Many produce fire by rubbing stones. They fish and hunt with bow and arrow, and live in leaf and straw community huts. And they don’t take kindly to intrusions.

Anil Thapliyal, a commander in the Indian coast guard, said he spotted the lone tribesman on the island of Sentinel, a 23-square-mile key, on December 28.

“There was a naked Sentinelese man,” Mr. Thapliyal said. “He came out and shot an arrow at the helicopter.”

According to varying estimates, there are only about 400 to 1,000 members alive today from the Great Andamanese, Onges, Jarawas, Sentinelese, and Shompens. Some anthropological DNA studies indicate their bloodlines go back 70,000 years. They originated in Africa and migrated to India through Indonesia, anthropologists say.

It appears that many tribesman fled the shores well before the waves hit the coast, where they would typically be fishing at this time of year.

After the tsunami, local officials spotted 41 Great Andamanese – out of 43 in a 2001 Indian census – who had fled the submerged portion of their Strait Island. They also reported seeing 73 Onges – out of 98 in the census – who fled to highland forests in Dugong Creek on Little Andaman Island, or Hut Bay, a government anthropologist said.

However, the fate of the three other tribes won’t be known until officials complete a survey of the remote islands this week, he said. The government reconnaissance mission will also assess how the ecosystem – most crucially, the water sources – has been damaged.