Archaeological evidence makes clear that domestic horses had similarly transformed human society on the Russian steppe much earlier, around 4000 BC. The steppe habitat of open grassland was hard for people to exploit until they could use horses to solve the problems of distance and transport. Human occupation of the Russian steppe accelerated with horse domestication and then exploded with the invention of ox-drawn wheeled vehicles around 3300 BC. The steppe economy came to be based on the combination of sheep and cattle for meat, milk, and wool, plus horses and wheeled vehicles for transport, and supplemented by a little farming.
There is no evidence for intensive agriculture and food storage at those early steppe sites, in marked contrast to the abundant evidence at other European and Mideast sites around the same time. Steppe people lacked large permanent settlements and were evidently highly mobile—again in contrast to the villages with rows of hundreds of two-storey houses in southeast Europe at the time. What the horsemen lacked in architecture, they made up for in military zeal, as attested by their lavish tombs (for men only!), filled with enormous numbers of daggers and other weapons, and sometimes even with wagons and horse skeletons.
Thus, Russia's Dnieper River (see map on page 243) marked an abrupt cultural boundary:, to the east, the well-armed horsemen, to the west, the rich farming villages with their granaries. That proximity of wolves and sheep spelt T-R-O-U-B-L-E. Once the invention of the wheel completed the horsemens' economic package, their artifacts indicate a very rapid spread for thousands of miles eastwards through the steppes of central Asia (see map). From that movement, the ancestors of the Tocharians may have arisen. The steppe peoples' spread westwards is marked by the concentration of European farming villages nearest the steppes into huge defensive settlements, then the collapse of those societies, and the appearance of characteristic steppe graves in Europe as far west as Hungary.
Of the innovations that drove the steppe peoples' steamroller, the sole one for which they clearly get full credit is the domestication of the horse. They might also have developed wheeled vehicles, milking, and wool technology independently of the Mideast's civilizations, but they borrowed sheep, cattle, metallurgy, and probably the plough from the Mideast or Europe. Thus, there was no single 'secret weapon' that alone explains the steppe expansion. Instead, with horse domestication the steppe peoples became the first to put together the economic and military package that came to dominate the world for the next 5,000 years—especially after they added intensive agriculture upon invading southeastern-Europe. Hence their success, like that of the second-stage European expansion that began in 1492, was an accident of bio-geography. They happened to be the peoples whose homeland combined abundant wild horses and open steppe with proximity to Mideastern and European centres of civilization.
As archaeologist Marija Gimbutas, from the University of California, Los Angeles, has argued, the Russian steppe peoples who lived west of the Ural Mountains in the fourth millenium BC fit quite well into our postulated picture of proto-Indo-Europeans. They lived at the right time. Their culture included the important economic elements reconstructed for PIE (like wheels and horses), and lacked the elements lacking from PIE (like battle chariots and many crop terms). They lived in the right place for PIE: the temperate zone, south of Finno-Ugric peoples, near the later homeland of Lithuanians and other Baits.
If the fit is so good, why does the steppe theory of Indo-European origins remain so controversial? There would have been no controversy if archaeologists had been able to demonstrate a rapid expansion of steppe culture from southern Russia all the way to Ireland around 3000 BC. But that did not happen; direct evidence of the steppe invaders themselves extends no further west than Hungary. Instead, around and after 3000 BC, one finds a bewildering array of other cultures developing in Europe and named for their artifacts (for instance, the 'Corded Ware and Battle-axe Culture'). Those emerging Western European cultures combine steppe elements like horses and militarism with old Western European elements, especially settled agriculture. Such facts cause many archaeologists to discount the steppe hypothesis altogether, and to see the emerging Western European cultures as local developments.
However, there is an obvious reason why the steppe culture could not spread intact to Ireland. The steppe itself reaches its western limit in the plains of Hungary. That is where all subsequent steppe invaders of Europe, such as the Mongols, stopped. To spread further, steppe society had to adapt to the forested landscape of Western Europe—by adopting intensive agriculture, or by taking over existing European societies and hybridizing with their peoples. Most of the genes of the resulting hybrid societies may have been the genes of Old Europe.
If steppe people imposed PIE, their mother tongue, on southeastern Europe as far as Hungary, then it was the resulting daughter Indo-European culture, not the original steppe culture itself, that spread to derived granddaughter cultures elsewhere in Europe. Archaeological evidence of major cultural change suggests that such granddaughter cultures may have arisen throughout Europe and east to India between WOO and 1500 BC. Many non-Indo-European languages held out long enough to be preserved in writing (like Etruscan), and Basque still survives today. Thus, the Indo-European steamroller was not a single wave, but a long chain of events that has taken 5,000 years to unfold.
As an analogy, consider how Indo-European languages came to dominate North and South America today. We have abundant written records to prove that they stem from invasions of Indo-European speakers from Europe. Those European immigrants did not overrun the Americas in one step, and archaeologists do not find remains of unmodified European culture throughout the sixteenth-century New World. That culture was useless on the US frontier. Instead, the colonists' culture was a highly modified or hybrid one that combined Indo-European languages and much of European technology (such as guns and iron) with American Indian crops and (especially in Central and South America) Indian genes. Some areas of the New World have taken many centuries for Indo-European language and economy to master. The takeover did not reach the Arctic until this century. It is reaching much of the Amazon only now, and the Andes of Peru and Bolivia promise to remain Indian for a long time yet.
Suppose that some future archaeologist should dig in Brazil, after written records have been destroyed and Indo-European languages have disappeared from Europe. The archaeologist will find European artifacts suddenly appearing on the coast of Brazil around 1530, but penetrating the Amazon only very slowly thereafter. The people whom the archaeologist finds living in the Brazilian Amazon will be a genetic mishmash of American Indians, blacks, Europeans, and Japanese, speaking Portuguese. The archaeologist will be unlikely to realize that Portuguese was an intrusive language, contributed by invaders, to a hybrid local society. Even after the PIE expansion of the fourth millenium BC, new interactions of horses, steppe peoples, and Indo-European languages continued to shape Eurasian history. PIE horse technology was primitive and probably involved little more than a rope-bit and bareback rider. For thousands of years thereafter, the military value of horses continued to improve with inventions ranging from metal bits and horse-drawn battle chariots around 2000 BC to the horseshoes, stirrups, and saddle of later cavalry. While most of these advances did not originate in the steppes, steppe peoples were still the ones who profited the most, because they always had more pasture and therefore more horses.
As horse technology evolved, Europe was invaded by many more steppe peoples, among whom the Huns, Turks, and Mongols are best known. These peoples carved out a succession of huge, short-lived empires, stretching from the steppes to Eastern Europe. But never again were steppe peoples able to impose their language on Western Europe.