Tracing the spread of languages has been difficult. Most linguists use changes in words or grammatical structures to try to track language evolution. The English word "brother," for example, translates as bhrater in Sanskrit, brathir in Old Irish, frater in Latin, and phrater in Greek. These differences can be used to reconstruct the ancient words that gave rise to these modern ones. But unlike genes, these cultural units cannot be traced back far enough to distinguish patterns of language change much earlier than about 6500 years ago.So Quentin Atkinson, a psychologist at the University of Auckland in New Zealand who has long worked on language evolution, decided to look at language units whose pedigrees might be traceable further back: phonemes, the smallest units of sound that allow us to distinguish one word from another. For example, the English words "rip" and "lip" differ by a single phoneme, one corresponding to the letter "r" and the other to 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 phoneme diversity. And, as also predicted if language arose in Africa, phoneme diversity was greatest in Africa and smallest in South America and Oceania (the islands of the Pacific Ocean), the points farthest from Africa, Atkinson reports online today in Science. The pattern matches that for human genetic diversity: As a general rule, the farther one gets from Africa—widely accepted as the ancestral home of our species—the smaller the differences between individuals within a particular population.
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