There is still another, completely independent approach to the dating problem—the science termed linguistic paleontology. Just as paleontologists try to discover what the past was like by looking for relics buried in the ground, linguistic paleontologists do it by looking for relics buried in languages.
To understand how this works, recall that linguists have reconstructed nearly 2,000 words of PIE vocabulary. It is not surprising that these include words like 'brother' and 'sky', which must have existed and been named since the dawn of human language. But PIE should not have had a word for 'gun', since guns were not invented until about 1300 AD, long after PIE-speakers had already scattered to speak distinct languages in Turkey and India. In fact, the word for 'gun' uses different roots in different Indo-European languages: 'gun' in English, fusil in French, ruzhyo in Russian, and so on. The reason is obvious: different languages could not possibly have inherited the same root for 'gun' from PIE, and they each had to invent or borrow their own word when guns were invented.
The gun example suggests that we should take a series of inventions whose dates we know, and see which of those do and which do not have reconstructed names in PIE. Anything—like gun—that was invented after PIE began to break up should not have a reconstructed name. Anything—like brother—that was invented or known before the break-up might have a name. (It does not have to have a name, because plenty of PIE words have surely become lost. We know the PIE words for 'eye' and 'eyebrow' but not'eyelid', although PIE speakers must have had eyelids.) Perhaps the earliest major developments without PIE names are battle chariots, which became widespread between 2000 and 1500 BC, and iron, whose use became important between 1200 and 1000 BC. The lack of PIE terms for these relatively late inventions does not surprise us, since the distinctness of Hittite had already convinced us that PIE broke up long before 2000 BC. Among earlier developments that do have PIE names, there are words for 'sheep' and 'goat', first domesticated by around 8000 BC; cattle (including separate words for cow, steer, and ox), domesticated by 6400 BC; horses, domesticated by around 4000 BC; and ploughs, invented around the time that horses were domesticated. The latest datable invention with a PIE name is the wheel, invented around 3300 BC.
Therefore, linguistic paleontology, even in the absence of any other evidence, would date the break-up of PIE as before 2000 BC but after 3300 BC. This conclusion agrees well with the one reached by extrapolating the differences between Hittite, Greek, and Sanskrit backwards in time. Hence if we wish to find traces of the first Indo-Europeans, we should be safe concentrating on the archaeological record between 2500 and 5000 BC, and perhaps slightly before 3000 BC. Having reached fair agreement about the 'when' question, let's now ask: where was PIE spoken? Linguists have disagreed about the PIE homeland ever since they first began to appreciate its significance. Almost every possible answer has been proposed, from the North Pole to India, and from the Atlantic to the Pacific shores of Eurasia. As the archaeologist J.P. Mallory puts it, the question is not, 'Where do scholars locate the Indo-European homeland? , but 'Where do they put it nowT
To understand why this problem has proved so difficult, let's first try to solve it quickly by looking at a map (see page 228). As of 1492, most surviving Indo-European branches were virtually confined to Western Europe, and only Indo-Iranian extended east of the Caspian Sea. Western Europe would be the most parsimonious solution to the search for the PIE homeland, the solution that required the fewest people to move long distances. Unfortunately for that solution, in 1900 a 'new' but long-extinct Indo-European language was discovered in a triply unlikely location. Firstly, the language (Tocharian, as it is now known) turned up in a secret chamber behind a wall in a Buddhist cave monastery. The chamber contained a library of ancient documents in the strange language, written around 600–800 AD by Buddhist missionaries and traders. Secondly, the monastery lay in Chinese Turkestan, east of all extant Indo-European speakers and about a thousand miles removed from the nearest ones. Finally, Tocharian was not related to Indo-Iranian, the geographically closest branch of Indo-European, but possibly instead to branches used in Europe itself, thousands of miles to the west. It is as if we suddenly discovered that the early medieval inhabitants of Scotland spoke a language related to Chinese.
Obviously, the Tocharians did not reach Chinese Turkestan by helicopter. They surely walked or rode there, and we have to assume that central Asia formerly had many other Indo-European languages that disappeared without the good fortune to be preserved by documents in secret chambers. A modern linguistic map of Eurasia (see page 228) makes obvious what must have happened to Tocharian and all those other lost Indo-European languages of central Asia. That whole area today is occupied by people speaking Turkic or Mongolian languages, descendants of hordes that overran the area from the time of at least the Huns to Genghis Khan. Scholars debate whether Genghis Khan's armies slaughtered 2,400,000 or only 1,600,000 people when they captured Harat, but scholars agree that such activities transformed the linguistic map of Asia. In contrast, most Indo-European languages known to have disappeared in Europe—like the Celtic languages Caesar found spoken in Gaul—were replaced by other Indo-European languages. The apparently European centre of gravity of Indo-European languages as of 1492 was actually an artifact of recent linguistic holocausts in Asia. If the PIE homeland really was centrally located in what became the Indo-European realm by 600 AD, stretching from Ireland to Chinese Turkestan, then that homeland would have been in the Russian steppes north of the Caucasus, rather than in Western Europe.
Just as the languages themselves gave us some clues to the time of PIE's break-up, so too they contain clues to the location of the PIE homeland. One clue is that the language family to which Indo-European has the clearest connections is Finno-Ugric, the family that includes Finnish and other languages native to the forest zone of north Russia (see map on page 228). Now it is true that the links between Finno-Ugric and Indo-European languages are enormously weaker than those between German and English, which stem from the fact that the English language was brought to England from northwest Germany only 1,500 years ago. The links are also much weaker than those between the Germanic and Slavic language branches of Indo-European, which probably diverged a few thousand years ago. Instead, the links suggest a much older propinquity between the speakers of PIE and of proto-Finno-Ugric. But since Finno-Ugric comes from the north Russian forests, that suggests a PIE homeland in the Russian steppe south of the forests. In contrast, if PIE had arisen much further south (say, in Turkey), the closest affinities of Indo-European might have been with the ancient Semitic languages of the Near East.
A second clue to the PIE homeland is the non-Indo-European vocabulary swept up as debris into quite a few Indo-European languages. I mentioned that this debris is especially noticeable in Greek, and it is also conspicuous in Hittite, Irish, and Sanskrit. That suggests that those areas used to be occupied by non-Indo-Europeans and were later invaded by Indo-Europeans. If so, the PIE homeland was not Ireland or India (which almost no one suggests today anyway), but it also was not Greece or Turkey (which some scholars still do suggest).