The peoples of India, Iran and Europe speak a Babel of tongues, but most — English included — are descended from an ancient language known as proto-Indo-European. Scholars have argued for two centuries about the identity and homeland of those who spoke this parent language, but a surprisingly sudden resolution of this longstanding issue may be at hand.

Many origins have been proposed for the birthplace of the Indo-European languages, but only two serious candidates are now under discussion, one of which assumes they were spread by the sword, the other by the plow.

Historical linguists can reconstruct many words of proto-Indo-European from their descendants. For example, there was probably a word “kwekwlos,” meaning wheel, which is the ancestor of “kuklos” in classical Greek, of “kakra” in Old Indic and – because K shifts to H in Germanic languages – of “hweohl” in Old English, itself the ancestor of wheel in modern English.

From the reconstructed vocabulary, the speakers of proto-Indo-European seem to have been pastoralists, familiar with sheep and wheeled vehicles. Archaeologists find that wheeled vehicles emerged around 4000 B.C., suggesting the proto-Indo-European speakers began to flourish some 6,500 years ago on the steppe grasslands above the Black and Caspian Seas. This steppe theory, favored by many linguists, holds that the proto-Indo-European speakers then spread their language to Europe, India and western China, whether by conquest or the appeal of their pastoral economy.