Early Brazilians unveil African look. (Science News of the week).

The stormy scientific debate over the origins of the first Americans has taken a surprising geographic turn. Human skulls unearthed in Brazil and ranging in age from about 8,000 to 11,000 years look more like modern Africans and Australian aborigines than like modern Asians or Native Americans, according to a report presented in Kansas City at last week's annual meeting of the American Association of Physical Anthropologists.

This finding contradicts the influential theory that Asians were the first to cross the now submerged Bering land bridge to North America around 12,000 years ago, says Walter A. Neves of the University of Sao Paulo. Instead, African migrants actually may have been the first to take this northern route into the Americas, theorizes Neves, who directed the Brazilian excavation and fossil analysis. At least 45,000 years ago, he adds, migrating Africans reached Australia via a southern route.

The exact timing of population movements that brought Africans to what is now South America remains unknown, the Brazilian scientist says.

"The anatomical similarities of Australians and the first South Americans are related to their shared African ancestry," Neves says. "We need to understand patterns of prehistoric human migration through Siberia much better."

In 1994 and 1995, Neves and his coworkers excavated Santana do Riacho 1, the largest known prehistoric burial site in the Americas. The researchers uncovered the skeletal remains of at least 40 individualsin 28 separate graves.

Radiocarbon analyses indicated that the burials occurred over a 3,000-year span, beginning about 11,000 years ago.

The Brazilian scientists compared measurements of the intact skulls of six adults--two men and four women--with those of skulls from modern populations of Africans, aboriginal Australians, Asians, and Native Americans.

The Santana do Riacho 1 skulls exhibited considerable variation in shape, Nevus remarks. However, they shared several traits with Africans and aboriginal Australians. These characteristics include a long, narrow brain case and eye sockets set relatively low on the face.

An 11,000-year-old skull found at another Brazilian site a decade ago displays these same traits, Neves adds.

He suspects that African-based travelers reached South America by land rather than by sea.

Other anthropologists familiar with the Brazilian skulls agree that they look African in some respects. However, they emphasize that the nature and timing of early forays into the Americas remain poorly understood (SN: 4/15/00, p. 244).

For example, skull measurements provide only ambiguous clues for untangling the evolution of populations, comments Richard L. Jantz of the University of Tennessee in Knoxville. If ancient Brazilian settlers exhibited a large amount of anatomical variability, it may be a coincidence that Neves found a few who show African similarities, Jantz says.

Moreover, the few available North American human skulls from 8,000 to 11,000 years ago bear little resemblance to modern populations, including Africans, he maintains. An analysis of the 8,400-year old skeleton of Kennewick Man, discovered in Washington State in 1996, revealed some anatomical links to modern Polynesians, further complicating this picture (SN: 5/15/99, p. 315).

Prehistoric humans everywhere shared many skeletal features that underwent regional modifications due to factors such as natural selection and random genetic changes, proposes Joseph F. Powell of the University of New Mexico in Albuquerque. Those influences, rather than a distinct African origin, may account for the Brazilian skulls' shape, he asserts.

"The Brazilian specimens have an African look," Powell says. "But what that means is anybody's guess."