BERKELEY, Calif. (AP) A decade ago, the timing of the first humans to reach the Americas seemed clear. Scientific opinion held that the ancestors of American Indians crossed the Bering Strait from Asia 11,000 or 12,000 years ago, after the last Ice Age, then fanned out across two continents.
Then, in 1989, University of California, Berkeley, linguist Johanna Nichols began a systematic look at Indian languages.
She traced language families, based on points such as how numbers were used, where a verb is placed in a sentence or even the "m" sound in pronouns, and decided that history was wrong. She found 150 language families in North and South America, a surprisingly high number since languages take time to develop into new tongues.
"I knew perfectly well that there's no way you could get 150 such language families in here, of such different types, in that time," Nichols says. "Whatever the age of the languages is, it's a great deal more than 11,000 years."
Using her research to analyze migration patterns, she found evidence to suggest that the Americas have been inhabited for 30,000 or 40,000 years — three times the generally accepted time frame. Moreover, there seemed to be several migratory waves.
In due course, microbiologists tracking DNA in Indian tribes announced similar conclusions, while archaeologists discovered a 12,500-year-old settlement in Monte Verde, Chile, which would have taken Asian settlers at least 6,000 years to reach.
At an American Association for the Advancement of Science conference last month, Nichols and other scientists on a panel discussing the first Americans found their once-rejected theories to now be mainstream.
"It's converging with archaeological evidence to the point that we're starting to feel reasonably confident that there were humans in the New World prior to 20,000 years ago," says David Meltzer, a Southern Methodist University archaeologist.
Archaeological finds seem to show that modern human migration, which apparently started in Africa 100,000 to 120,000 years ago, occurred much faster than once believed.
Nichols, who began her career teaching Slavic languages at Berkeley in 1972, explored a mathematical pattern in how Indian languages evolved into new tongues. On average, each of the oldest language families developed into 1.5 language families every 6,000 years, she says. By dividing the number of language families by that factor, she came up with an estimate of how far back an area was settled.
A pattern emerged. The first wave or two of migrants from Asia arrived 30,000 to 40,000 years ago, and the settlers spread out, perhaps thinly, through the Americas.
Then the last Ice Age arrived, lasting from 22,000 years ago to 14,000 years ago. The first Americans, researchers suggest, apparently remained in South America during the climate change.
After the Ice Age, "it looks to me like language spread north from somewhere — perhaps the Gulf Coast or Central America — into North America," Nichols says.
As the first settlers headed north, a new wave of migrants was arriving across the Bering Strait from Asia. They were different both in language and culture from the older natives, Nichols said, and seemed to remain west of the Sierra Nevada in North America and of the Andes in South America.
In a final wave, the ancestors of modern-day Eskimos arrived from Asia about 5,000 years ago, staying in what is now Alaska, Canada and Greenland.
Nichols estimates that the world's languages in general have developed over a 120,000-year period. Does that mean there is an ancient mother tongue?
Nichols is cautious.
"It could be that all the world's languages accidentally go back to just one of the ones that was spoken then," she says, but there is no way to be sure — yet.