One of the reasons we have some "history" is that they picked up, purchased, collected, seized, or otherwise laid hands on Greek scribes to take with them to write down important information ~ navigational hints, bills, deliveries, news about the gods, etc.
The Galicians in Spain claim their earliest materials (copied by hand down through the centuries like all ancient documents) are written in ancient Greek for example.
The seagoing Celts weren't the only people to do that, and Greek scribes were always highly prized and sought after.
I suspect in earlier times OTHERS found it advantageous to capture Middle Eastern agricultural technicians and use them as slaves in the "royal gardens".
Else we'd have to believe two possible other tales ~ (1) That Middle Eastern settlers could move into occupied hunting grounds in Europe and just start farming without difficulty, or (2) That primitive hunter/gatherers went to the Middle East to study farming and then returned!
Since Western Europeans look more like the Sa'ami than they do like the Arabs, I simply have to opt for the slavery option.
With the exception of a very few highly favored locations around the world, hunter-gatherers never developed anything much above the band or tribe level of organization. Not a dense enought population.
So they never had kings or royal gardens. Such things show up only with agriculture.
What I find most interesting is that these finds show the early history of Europe to be much like that of the US. More advanced agriculturists moving in from the east, pushing the less-advanced natives before them or wiping them out.
The archaeologists and anthropologists never tire of postulating some time in the distant past where things were handled peacefully, but whenever actual evidence turns up it seems to indicate our ancestors were all remarkably warlike.
That's why they became our ancestors. The unwarlike or those who were insufficiently efficient at war died, killed by our ancestors.
(3) Farmers from the Middle East, with the dense populations made possible by farming, were able to move into lands very thinly settled by hunters and push them out.
I'm not sure why that's hard to believe. It's exactly what Americans and Australians did.
Not to mention Bantus, Malays and a great many other peoples.
What we’ll see is that ancient peoples had much greater contact through trade and migration than we currently realize.
Intermarriage had to occur or tribal systems would collapse under their own genetic weight.
Have you checked out Dienekes blog? He blogs on genetic research. It can get very recondite and technical but it is of interest.