Language May Have Helped Early Humans Spread Out of Africa

The story of humanity's prehistoric expansion across the planet isrecorded in our genes. And, apparently, the story of the spread oflanguage is hidden in the sounds of our words. That's the finding of anew study, which concludes that both people and languages spread outfrom an African homeland by a similar process—and that language may havebeen the cultural innovation that fueled our ancestors' momentous migrations.

Tracing the spread of languages has been difficult. Most linguistsuse changes in words or grammatical structures to try to track languageevolution. The English word "brother," for example, translates as bhrater in Sanskrit, brathir in Old Irish, frater in Latin, and phraterin Greek. These differences can be used to reconstruct the ancientwords that gave rise to these modern ones. But unlike genes, thesecultural units cannot be traced back far enough to distinguish patternsof language change much earlier than about 6500 years ago.

So Quentin Atkinson, a psychologist at the University of Auckland inNew Zealand who has long worked on language evolution, decided to lookat language units whose pedigrees might be traceable further back:phonemes, the smallest units of sound that allow us to distinguish oneword from another. For example, the English words "rip" and "lip" differby a single phoneme, one corresponding to the letter "r" and the otherto the letter "l."

Atkinson looked at the phonemes from 504 languages across the world, using as his database the authoritative online World Atlas of Language Structures,which includes phonemes based on differences in the sounds of vowels,consonants, and spoken tones. He then constructed a series of models,demonstrating first that smaller populations have lower phonemediversity. And, as also predicted if language arose in Africa, phonemediversity was greatest in Africa and smallest in South America andOceania (the islands of the Pacific Ocean), the points farthest fromAfrica, Atkinson reports online today in Science. The patternmatches that for human genetic diversity: As a general rule, the fartherone gets from Africa—widely accepted as the ancestral home of ourspecies—the smaller the differences between individuals within aparticular population.

Controlling for differences in population size and other potentiallyconfounding factors, Atkinson then modeled the worldwide languagephoneme pattern that would be expected if human language had spread from2560 different potential points of origin around the planet. He foundthat the model that best fit present-day phoneme diversity patterns wasone that put the origins of all languages in central and southern Africa.

Atkinson's best-fit model parallels not only the overall geneticpattern, suggesting an out-of-Africa migration of modern humans, butalso subsequent events in human prehistory. Thus outside of Africa, thegreatest phoneme diversity was found in languages thought to have arisenin Southeast Asia, consistent with high genetic diversity there. Thissuggests that Southeast Asian populations grew very rapidly soon afterour ancestors left Africa. And within the Americas, phoneme diversitywas smaller the farther a population was from the Bering Strait,consistent with assumptions that the first Americans came over thestrait from Asia and spread as far as South America.

These parallels also suggest that human language predates theout-of-Africa migrations of 50,000 to 70,000 years ago. Atkinsonconcludes that language might have been the essential cultural andcognitive innovation that fueled human colonization of the globe.

Robin Dunbar, a psychologist at the University of Oxford in theUnited Kingdom, says Atkinson's study is a "really novel approach" thatovercomes the limitations of earlier studies. "The key to this was usingphoneme diversity rather than words or grammar." And Dunbar agrees withAtkinson that language evolution might have been "crucial infacilitating" the African exodus.

Bart de Boer, a linguist at the University of Amsterdam, adds thatthe paper "looks methodologically quite sound." But he says he issurprised that phonemes can be used to trace language evolution so farback in time—and that over the course of tens of thousands of yearsphoneme diversities in far-flung areas of the world have not "driftedback to the sizes found in Africa" because cultural evolution ofphonemes is "much faster than genetic evolution." De Boer says that hewould be happy if the paper turns out to be correct, but researchersmust first be sure that its conclusions are not "caused by somemethodological artifact we have all missed."