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"No matter how we [changed] the analysis or assumptions, we couldn't get a date of around 6,000 years," says Gray.
"This kind of study is exactly what linguistics needs," says April Mc Mahon, who studies the history of languages at the University of Sheffield, UK.
"The genetic evolution of humans in the very recent past might in some ways be linked to the cultural evolution," he said.
Other scientists urge great caution in interpreting the research.
Aside from not knowing what the gene variants actually do, no one knows how precise the model Lahn used to date them is, Collins added.
Lahn's own calculations acknowledge that the microcephalin variant could have arisen anywhere from 14,000 to 60,000 years ago, and that the uncertainty about the ASPM variant ranged from 500 to 14,000 years ago.
Words are better understood than grammar as a guide to language history; the same sentence structure can arise independently in different tongues.
The resulting tree matches many existing ideas about language development.
Lahn and colleagues examined two genes, named microcephalin and ASPM, that are connected to brain size.That does not mean one population is smarter than another, Lahn and other scientists stressed, noting that numerous other genes are key to brain development."There's just no correlation," said Duke's Wray, calling education and other environmental factors more important for intelligence than DNA anyway. The information contained in the AP News report may not be published, broadcast, rewritten or redistributed without the prior written authority of The Associated Press.Russell Gray and Quentin Atkinson, of the University of Auckland in New Zealand use the rate at which words change to gauge the age of the tree's roots - just as biologists estimate a species' age from the rate of gene mutations.The differences between words, or DNA sequences, are a measure of how closely languages, or species, are related.
The work was funded by the Howard Hughes Medical Institute. A family tree of Indo-European languages suggests they began to spread and split about 9,000 years ago.