Baja skulls shake up American ancestry.

Around 600 years ago, the Pericu people roamed the southern tip of what is now Mexico's Baja peninsula, a finger of land that extends below California. Although the Spanish conquest spelled their demise in the 16th century, the Pericu were living links to America's first settlers, according to a new anthropological study.

Pericu skulls closely resemble 8,000-to-11,000-year-old human skulls unearthed in Brazil, say Rolando Gonzalez-Jose of the University of Barcelona, Spain, and his colleagues. The Brazilian skulls look strikingly like those of today's Australian aborigines (SN: 4/7/01, p. 212). Moreover, the scientists contend, the data indicate that the Pericu were unrelated to modern Native American and eastern Asian groups.

These findings support the scientists' theory that both the first Americans, who arrived at least 12,000 years ago, and the first Australians, who showed up down under around 40,000 years ago, have a common root in southern Asia. A second wave of American settlers, the ancestors of present-day Native Americans, immigrated from northeastern Asia a mere several thousand years ago, Gonzalez-Jose's group concludes in the Sept. 4 Nature.

That scenario clashes with the traditional view that both the initial and later waves of American settlers came from northeastern Asia.

"Slowly, we are realizing that the ancestry of the Americas is as complex and as difficult to trace as that of other human lineages around the world," comments anthropologist Tom D. Dillehay of the University of Kentucky in Lexington.

Gonzalez-Jose and his coworkers compared measurements of 33 Pericu skulls housed at a Mexican museum with those of 22 ancient Brazilian skulls and hundreds of skulls from a worldwide sample of contemporary groups.

The Baja and Brazilian skulls exhibit telling similarities, the investigators say. These include long, narrow braincases and short, thin faces, a pattern akin to that of modern inhabitants of southern Asia and South Pacific islands.

The Pericu and the ancient Brazilians were descendents of America's initial settlers, the scientists propose. After the last ice age ended around 10,000 years ago, they add, the expansion of a desert across the middle of the Baja peninsula isolated the Pericu from other Native American groups.

Some of the continent's first arrivals probably traveled south along the Pacific coast from Alaska to reach the Baja peninsula's southern tip, Gonzalez-Jose says. Researchers typically theorize that after trekking through Alaska, the first Americans headed south through an inland ice corridor.

It's still unclear whether the Baja population descended from the continent's ancient settlers or grew to resemble prehistoric Brazilians by virtue of adapting to a New World environment that's similar to Brazil's, Dillehay says.

According to archaeologist David J. Meltzer of Southern Methodist University in Dallas, the next step is to extract DNA from the Baja and Brazilian skulls and determine whether the two groups had close genetic ties. For now, Meltzer remains convinced by skeletal and archaeological evidence that points to Siberia as the homeland of America's first settlers.