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Hundreds of languages, from English to Hindustani, are all derived from a single ancestral tongue. Now DNA from ancient bones suggests that the people who spoke this ancient language lived somewhere south of the Caucasus mountains in western Asia.

Languages evolve and diversify, much like biological species. Today, about 3 billion people today speak an Indo-European language, such as English, Spanish, Hindustani and Nepali. All these languages are descended from a single common ancestor.

This hypothetical ancient language, Proto-Indo-European (PIE), was spoken somewhere in Eurasia some time between about 5500 and 9000 years ago. But linguists are unsure where.

There are two leading ideas. The PIE homeland was either on the western Eurasian steppe somewhere north of the Caucasus mountains, or somewhere to the south of those mountains, perhaps in the Fertile Crescent in western Asia.

Indo-European languages were ultimately spoken in both regions. This suggests that the ancient inhabitants of the Caucasus mountains, which lie directly between the two proposed homelands, might hold crucial clues.

Across the mountains

To investigate, at the Max Planck Institute for the Science of Human History in Jena, Germany, and his colleagues examined DNA from 45 ancient humans, who lived in the Caucasus region between about 3200 and 6500 years ago.

The ancient DNA suggested that genes 鈥� and people 鈥� were flowing through the Caucasus mountains 6500 years ago. But the flow appears to have been largely one-way: from south to north.

The people living in the northern region of the Caucasus mountains 6500 years ago had genes similar to those previously detected in prehistoric farmers who lived in the north-east Fertile Crescent, in western Iran. What鈥檚 more, this 鈥淚ranian farmer鈥� genetic signature also spread onto the Eurasian steppe.

If DNA spread north through the Caucasus mountains and onto the Eurasian steppe 6500 years ago, it鈥檚 possible that languages did too. The researchers conclude that the PIE homeland may have been south of the Caucasus.

Haak is unable to comment on the findings yet, because the study is currently going through peer review.

Steppe or crescent?

A PIE homeland south of the Caucasus mountains makes sense, says linguist , who also works at the Max Planck Institute for the Science of Human History but was not involved in the study.

He points to that suggested the prehistoric people inhabiting the Eurasian steppe had . 鈥淏ut it鈥檚 much clearer now that the direction of the spread is going from south to north,鈥� he says.

However, Haak鈥檚 study goes against the trend, as in recent years the idea that the PIE homeland was on the Eurasian steppe has been gaining popularity.

This is largely because earlier ancient DNA studies have indicated that about 4800 years ago. This migration may have carried Indo-European languages into parts of Europe at this time.

The true birthplace

The problem with this idea is that the timings don鈥檛 match, as linguists think PIE was spoken significantly earlier than 4800 years ago.

Instead, Heggarty argues that PIE emerged in or near the northern Fertile Crescent, and some Indo-European languages were then carried north onto the Eurasian steppe 鈥� from where they moved west into Europe 4800 years ago.

鈥淓ven if several branches of Indo-European in Europe came from the steppe, it doesn鈥檛 mean you鈥檝e won the argument about where the ultimate homeland was,鈥� says Heggarty. 鈥淚f you鈥檙e looking for the PIE homeland, then you鈥檙e looking for where it all started, not just some of the branches.鈥�

The argument is unlikely to be settled any time soon. Linguist of the University of Pennsylvania in Philadelphia still favours the Eurasian steppe as the PIE homeland, which he says is more compatible with the archaeological record. However, he agrees that the southern option is not ruled out.