Here begins on of the last chapters inthe human story - the peopling of the americas.
Most scientists agree that today's Native Americans descend from ancient Asians who crossed from Siberia to Alaska in the last ice age, when low sea levels would have exposed a land bridge between the continents.
They probably traveled along the coast - perhaps a few hundred people moving from one piece of land to the next, between a freezing ocean and a wall of ice.
"A coastal route would have been the easiest way in," says Wells. "But it still would have been a hell of a trip.
Once across, they followed the immense herds of animals into the mainland and spread to the tip of South America in as little as a thousand years.