PEOPLING AMERICA
La peuplement des Amériques
De quand date l’arrivée des premiers hommes sur le continent américain ? Pendant longtemps, cette question a divisé la communauté scientifique mondiale, plus précisément celle des archéologues et des anthropologues. Un linguiste arrivera-t-il à réconcilier les deux camps ?
How America was originally colonised is a topic of perennial interest at the American Association for the Advancement of Science. Until recently, the earliest uncontested archaeological evidence of people living in the New World came from Swan Point, in Alaska. This dates back 14,400 years.
2.Linguists, however, maintain that the diversity of native languages in the Americas could not have arisen so quickly. Conventional models of linguistic evolution assume tongues separate in the way populations of organisms do—so that the flow of vowels, words and grammatical structures between groups must cease before new languages can emerge, just as a cessation of gene flow gives rise to new species.
3.This suggests it would take at least 50,000 years for a single population speaking a single language to diversify and spread through the Americas in a way that yielded the pattern heard today. Since Native Americans’ genes do, indeed, indicate they all derive from a single population, this discrepancy in timing is a paradox.
25,000 YEARS
4. That paradox may be close to resolution. Recent digs have pushed the physical evidence of America’s settlement back in time. Meanwhile, as the meeting heard from Mark Sicoli, a linguist at the University of Virginia, in Charlottesville, a different model of linguistic evolution brings the common ancestor of Native-American tongues forward. Apply a few error bars to the results and the two estimates touch—at about 25,000 years ago.
5.The problem with explaining linguistic evolution in pure Darwinian terms is that words are not genes. Species, once separate, do not exchange genetic information because they do not interbreed. Languages, though, can exchange grammatical and semantic elements when they meet, which can speed up diversification. Dr Sicoli thus turned to computational phylogenetic analysis, an area of linguistic research that tries to work out whether and how such interaction may have taken place.
CALCULATIONS
6. From the thousand or so Native-American languages he chose four dozen spoken in Alaska and northern Canada, the part of the Americas closest to humanity’s point of entry from Asia. He and his colleagues created a database that recorded, for each of them, 116 linguistic features such as sounds, parts of words, the functions of these parts and the ways a language combines words into phrases.
7.They then used this to identify the influences of languages on each other. They also added geographical information, plotting the flow of linguistic change along the Pacific coast and through the river valleys. This nearly halved the time needed to give rise to the modern situation if the languages had evolved independently from a single common ancestor. That suggests the process of divergence may have begun as recently as 25,000 years ago.