Dr. Spoor’s predictions were drawn from a digital reconstruction of the disturbed remains of the jaws of the original 1.8 million-year-old Homo habilis specimen found 50 years ago by the legendary fossil hunters Louis and Mary Leakey at Olduvai Gorge in Tanzania.

The reconstruction, suggesting a plausible evolutionary link between A. afarensis and H. habilis, yielded a remarkably primitive picture of a deep-rooted diversity of a species that emerged much earlier than the 2.3 million years ago suggested by some specimens. The teeth and jaws appeared to be more similar to A. afarensis than to subsequent Homo erectus or Homo sapiens, modern humans that emerged about 200,000 years ago.

Dr. Spoor’s analysis also seemed to put a new face on H. habilis. He said that individual species of early Homo are more easily recognizable by jaw structure and facial features than by differences in brain size, which tend to be highly variable. Dr. Villmoare and colleagues made similar observations in their article. Both the predictions and the mandible findings called attention to smaller teeth with the emergence of H. habilis and evidence suggesting that the species probably split in different evolutionary lines, only one of which might have been ancestral to later H. erectus and H. sapiens.