In 2003 Dr. Atkinson and Russell Gray, another biologist at the University of Auckland, reconstructed the tree of Indo-European languages with a DNA tree-drawing method called Bayesian phylogeny. The tree indicated that Indo-European was much older than historical linguists had estimated and hence favored the theory that the language family had diversified with the spread of agriculture some 10,000 years ago, not with a military invasion by steppe people some 6,000 years ago, the idea favored by most historical linguists.

“We’re uneasy about mathematical modeling that we don’t understand juxtaposed to philological modeling that we do understand,” Brian D. Joseph, a linguist at Ohio State University, said about the Indo-European tree. But he thinks that linguists may be more willing to accept Dr. Atkinson’s new article because it does not conflict with any established area of linguistic scholarship.

“I think we ought to take this seriously, although there are some who will dismiss it out of hand,” Dr. Joseph said.

Another linguist, Donald A. Ringe of the University of Pennsylvania, said, “It’s too early to tell if Atkinson’s idea is correct, but if so, it’s one of the most interesting articles in historical linguistics that I’ve seen in a decade.”

Dr. Atkinson’s finding fits with other evidence about the origins of language. The Bushmen of the Kalahari Desert belong to one of the earliest branches of the genetic tree based on human mitochondrial DNA. Their languages belong to a family known as Khoisan and include many click sounds, which seem to be a very ancient feature of language. And they live in southern Africa, which Dr. Atkinson’s calculations point to as the origin of language. But whether Khoisan is closest to some ancestral form of language “is not something my method can speak to,” Dr. Atkinson said.

His study was prompted by a recent finding that the number of phonemes in a language increases with the number of people who speak it. This gave him the idea that phoneme diversity would increase as a population grew, but would fall again when a small group split off and migrated away from the parent group.

Such a continual budding process, which is the way the first modern humans expanded around the world, is known to produce what biologists call a serial founder effect. Each time a smaller group moves away, there is a reduction in its genetic diversity. The reduction in phonemic diversity over increasing distances from Africa, as seen by Dr. Atkinson, parallels the reduction in genetic diversity already recorded by biologists.