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The conclusion will be controversial, as there is no consensus on where Indo-European languages came from.

Some linguists believe that Kurgan horsemen carried them out of central Asia 6,000 years ago.

So suggests new research that tracked changes in two genes thought to help regulate brain growth, changes that appeared well after the rise of modern humans 200,000 years ago.

Years later, a ruler declares one of those copies the definitive manuscript, and a rush is on to make many copies of that version — so whatever changes from the original are in this presumed important copy become widely disseminated.

Scientists attempt to date genetic changes by tracing back to such spread, using a statistical model that assumes genes have a certain mutation rate over time.

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.

"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.Gray and Atkinson analysed 87 languages from Irish to Afghan.Rather than compare entire dictionaries, they used a list of 200 words that are found in all cultures, such as 'I', 'hunt' and 'sky'.In fact, the variations were so common they couldn't be accidental mutations but instead were probably due to natural selection, where genetic changes that are favorable to a species quickly gain a foothold and begin to spread, the researchers report.Lahn offers an analogy: Medieval monks would copy manuscripts and each copy would inevitably contain errors — accidental mutations.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.