Modern humans linked to single origin.

A new study that calculates the mathematical fit of competing explanations of human evolution with the geographic array of specific fossil features supports a single African or southwest Asian origin for modern humans.

The analysis enters a heated debate over human origins. One theory posits an Mrican genesis for modern humans between 100,000 and 200,000 years ago, after which Homo saplens spread elsewhere and replaced Neandertals. An opposing view argues that modern humans evolved simultaneously in several parts of the world beginning about I million years ago, with genetic input from Neandertals (SN: 9/25/93, p. 196).

"Africa and southwest Asia are good candidates for areas where modern human anatomy originated," asserts Diane M. Waddle, an anthropologist at Duke University Medical Center in Durham, N.C. "I'm confident that Neandertals had nothing significant to do with modern human evolution."

Waddle's study relies on a method, developed by geneticist Robert R. Sokal of the State University of New York at Stony Brook, for calculating the correspondence between various scientific predictions and sets of relevant data. Sokal and his coworkers have used this method to evaluate theories of modern language origins based on links between language patterns and genetic traits in European populations (SN: 8/22/92, p.!17).

The Duke scientist studied 83 fossil craniums of H. saplens and Neandertals found at sites in Europe, southwest Asia, and Africa. Specimens ranged in age from around 40,000 to 400,000 years old. Waddle placed the fossils in 12 groups, depending on geographic location and age.

She then measured a series of cranial features and traits to calculate the anatomical variation in each group and the degree to which pairs of groups resembled one another.

Considered either as separate origin sites or lurepeal into a single group, African and southwest Asian fossils account better for the resulting pattern of anatomical relationships than the assumption that evolution took distinctive paths in Africa, Asia, and Europe, Waddle contends in the March 31 NATURE.

Advocates of multiregional human evolution, such as Alan G. Thorne of Australian National University in Canberra, doubt that Waddle's conclusion will hold up once she studies East Asian and Australian fossils. Waddle plans to analyze these specimens, which have often been cited in defense of a separate Asian evolution of modern humans.