Life used to be simple. When one of my sons would ask "Daddy, where do I come from?" I would say "The Eurasian Steppes. Just like all speakers of Indo-European languages." That would usually end the conversation pretty quickly. When they read this, they may leave off reading as soon as they see Indo-European. It became my go-to conversation killer when I wanted time to myself.
(Side note: My oldest son now has a daughter of his own so presumably he learned the answer to his real question somehow. I don't know where. The streets, probably.)
I have grown less certain about that answer over the years, and all goes dark before my eyes. If you can't trust the past to stay put, what can you trust? The prevailing theory on the Indo-European homeland for decades included warriors and horses. Lots of warriors, lots of horses. Clever warriors from the Eurasian steppes domesticated horses, hitched them up to chariots, and set out in all directions to conquer everyone with this new advanced military trick. They invaded India, Iran, Turkey, Southern Europe, and Northern Europe – not all at once, but pretty darn close together. Starting in about 4000 BC they moved outward, and by 2500 BC had pretty much conquered all the lands above, installing their daughter languages (Indo-Iranian, Proto-Celtic, etc) everywhere.
Linguists, who developed this theory, waited for the archaeologists to uncover all the stuff that would prove it. They’re still waiting. The archaeologists have found lots of interesting stuff, but evidence of invasions seems to be lacking. Without invasions, there aren’t good reasons for the various peoples of Europe and India to have started speaking all these versions of Indo-European. Most people would rather just go on speaking their own language, thank you very much. So there’s some problem, some contradiction there.
The idea of a small warrior elite caught on for awhile, ruling all these places but not actually overrunning them, enforcing their languages on everyone. That fell apart too, as language enforcement over vast areas is difficult even for empires, and there weren’t even any empires then.
On the plus side, we did learn a lot about the religious and social practices of some tribe that lived on the Eurasian Steppes, who probably are connected with us somehow.
Colin Renfrew To the (Temporary) Rescue. In the late 80's Renfrew put forth his idea that this tribe of our supposed ancestors started centuries earlier, from Anatolia (Turkey), and were farmers instead. These farmers took the agricultural technology of the Middle-East - herding and grain crops - and lit out for the territories. Nasty discussions developed whether these farmers displaced the previous inhabitants - which would explain the language spread - or the new technology just gradually spread into the Balkans, Europe, and the Eurasian Steppes - which would leave no convenient explanation why the other tribes would pick up a new language along with the sheep and the barley. Hey, we admire you Indo-European farmers so much we'd like to have one of your languages, too. We'll need about a half-dozen at first.
Supporting this theory is that it gets around the problem of no invasions quite nicely. No invasions needed. Lots of skirmishes, maybe, but constant warfare with neighboring tribes is pretty much the history of human beings for thousands of years, so no loss there. If my easy acceptance of violence toward neighbors distresses you, consider this: who else would they fight with? Why go three tribes over to skirmish? What would be the point of that? Sheesh.
Renfrew's theory also works well with more recent glottochronology and recreation of probable language trees. 6,000 years doesn't look like enough time anymore. 8,000, maybe even 10,000 looks better. There's some grumbling among linguists about that - 6K seemed okay, 8K might be allowable, but 10K, no way. Language changes too quickly, they say.
But it is the new genetic evidence that has everyone in a funk. As Bryan Sykes has discovered, the genetic background of Europeans is only 15% from that wave of farmers coming up in 5000BC. 80% of Europe's genes look like they've been right there since Paleolithic times. While Paleolithic includes everything up to about 11,500 BC, the most recent wave of settlers to Europe came well before that date. 15-20,000 years ago, that 80% chunk of Europe's genetic heritage arrived. That's about 10,000 years of problem, linguistically. Hard to sweep under the rug. As I noted above, that works out if it's just the farming technology that moves from the Balkans into Europe, and the people pretty much stay where they are. But why everyone would start speaking a new language remains unanswered.
The Paleolithic Continuity Theory suggests that they were already speaking daughter languages of Proto-Indo-European when they arrived. The Celts were speaking Celtic, Slavs Slavic, Balts Baltic, etc. Very neat. Very tidy. No need to dream up some reason for them to switch languages. What happened in historical times, with Italic-speakers and Germanic-speakers pushing the Celts around in the years AD is a completely separate issue, of no interest to the Indo-Europeanists. What all those hunter-gatherers were speaking before the farming came in is their concern.
That still leaves a fairly large problem however. How did those people speak languages that hadn't been invented yet? That wouldn't be invented for 10,000 years, in fact? The Italian linguists who are behind all this have a nifty explanation: language changes much more slowly than we thought. Slower than half the speed. In their telling, Indo-European was developed during the last Ice Age, when everyone was crammed into southern Europe. As the ice receded, that tribe was the dominant one moving back into the territory. A few stragglers related to the Basques, who had survived in Europe in isolated pockets that the ice missed, were easily pushed back into corners or eliminated altogether.
This all makes the linguists openly contemptuous - which linguists do very well, BTW, even to each other. Especially to each other. They were willing to flex maybe 2000 years on the start of the language family, but not 10,000 years. Impossible. Language changes too quickly for that.
Well, we'll see. I remain undecided - I think a stretched version of Renfrew's Anatolian view is still possible, but PCT is certainly intriguing.