11:24 04 September 03

NewScientist.com news service

Skull measurements on the remains of an isolated group of people who lived at the southern tip of Mexico's Baja California has stirred up the debate on the identity of the first Americans once again.

The earliest inhabitants of North America differed subtly but significantly from modern native Americans. The difference is clearly seen in the skull shapes of the first people to colonise the continent, who had longer, narrower skulls than modern people.

One theory says it is because two distinct groups of people migrated to North America at different times. But another theory says that just one population reached the continent and then evolved different physical attributes, except for a few isolated groups.

Anthropologists once assumed the earliest Americans resembled modern native Americans. That changed with the discovery of a 10,500-year-old skeleton called Luzia in Brazil, and the 9000-year-old skeleton of Kennewick man in Washington state.

[B]Both had the long, narrow skulls that more resemble those of modern Australians and Africans than modern native Americans, or even the people living in northern Asia, who are thought to be native Americans' closest relatives.[/B]

Some researchers argued that they were simply unusual individuals, but scientists have now identified the same features in recent remains from the Baja California.

Desert island

The Pericú hunter-gatherers survived until just a few hundred years ago at the end of the peninsula, says Rolando González-José, of the University of Barcelona, Spain, (Nature, vol 425, p 62).

He thinks the formation of the Sonora desert isolated the Pericú for thousands of years, but they vanished when Europeans disrupted their culture. González-José measured 33 Pericú skulls and found their features were similar to those of the ancient Brazilian skulls.

This backs the idea that a first wave of long, narrow skulled people from south-east Asia colonised the Americas about 14,000 years ago. These were followed by a second wave of people from north-east Asia about 11,000 years ago, who had short skulls.

This theory has been championed by Walter Neves, at the University of Sao Paulo, Brazil. He says the second wave may have been larger, and eventually came to dominate the Americas. "The discovery is exactly what I have been predicting since the late 1980s," Neves told New Scientist.

However Joseph Powell, an anthropologist at the University of New Mexico in Albuquerque, is not convinced. He thinks the earliest Americans did come from south-east Asia, but believes they evolved into modern native Americans.

"Even with two waves, each would have changed over the past 10,000 to 12,000 years through adaptation and microevolution," he says. Neves argues that the change in skull shape after 8000 years ago is too sudden for evolution.

Journal reference: Nature (vol 425, p 62)

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