Those criticisms are particularly important, Collins said, because Lahn's testing did find geographic differences in populations harboring the gene variants today.They were less common in sub-Saharan African populations, for example.
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 The information contained in the AP News report may not be published, broadcast, rewritten or redistributed without the prior written authority of The Associated Press.
"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.
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.
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.
The finding hints that farmers in what is now Turkey drove the language boom - and not later Siberian horsemen, as some linguists reckon.
"We, including scientists, have considered ourselves as sort of the pinnacle of evolution," noted lead researcher Bruce Lahn, a University of Chicago geneticist whose studies appear in Friday's edition of the journal Science.
"There's a sense we as humans have kind of peaked," agreed Greg Wray, director of Duke University's Center for Evolutionary Genomics.
Spanish and Portuguese come out as sisters, for example - both are cousins to German, and Hindi is a more distant relation to all three.