When a young child asks "where did I come from" the question can be answered quite simply, albeit perhaps a bit self-consciously. Determining just how the first humans arrived in the Americas, in contrast, has proved remarkably difficult. One theory holds that the first people to enter the New World came from northeast Asia about 12,000 years ago and were the direct ancestors of present-day Native Americans. But fossils bearing similarities to populations from south Asia and the southern Pacific Rim have posed difficulties for this explanation. A study published today in the journal Nature adds further fuel to the debate over the peopling of the New World, supporting a more varied geographical history for the first Americans.

Rolando González-José of the University of Barcelona and his colleagues examined 33 modern Amerindian skulls recovered from the tip of the Baja peninsula in Mexico. Studying numerous cranial traits, the team took detailed measurements in order to compare the remains with those from other sites. They found that the skulls showed a stronger resemblance to so-called Paleoamericans, who arrived from south Asia and the Pacific Rim, than they do to Paleoindian remains that have been linked to northeast Asia and Mongolia. Tom D. Dillehay of University of Kentucky notes in an accompanying commentary that the "new data add to accumulating evidence of morphological differences between early humans from different areas of the Americas."

More early human remains will be needed to obtain a clearer picture of the initial colonization of the Americas. Notes Dillehay, "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."