For the microcephalin gene, the variation arose about 37,000 years ago, about the time period when art, music and tool-making were emerging, Lahn said.
For ASPM, the variation arose about 5,800 years ago, roughly correlating with the development of written language, spread of agriculture and development of cities, he said.
"A different way to look at is it's almost impossible for evolution not to happen." Still, the findings also are controversial, because it's far from clear what effect the genetic changes had or if they arose when Lahn's "molecular clock" suggests — at roughly the same time period as some cultural achievements, including written language and the development of cities.
The resulting tree matches many existing ideas about language development."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.Spanish and Portuguese come out as sisters, for example - both are cousins to German, and Hindi is a more distant relation to all three.All other Indo-European languages split off from Hittite, the oldest recorded member of the group, between 8,000 and 10,000 years ago, the pair calculates.