My favorite example is the writings of Onfim, who was a little boy in the 1200s in present day Russia whose scribbling and homework were exquisitely preserved on birch bark fragments. It’s so immediately recognizable as a little boy’s endearing doodles about knights and imaginary beasts, yet its 800 years old.
Edit: I'm also curious how much time (thousands of years) for there to be noticeable difference in the capability of the brain like abstract thinking. Language may be the real problem.
It's not thousands of years. French Canadians are enriched for some of the same brain-related defects that Ashkenazi Jews can get; we assume for the same reasons.
> Which defects?
Ashkenazi Jews are prone to a whole host of genetic defects that affect the brain, of which the most famous is Tay-Sachs.
> What reasons?
A lifestyle focused on commerce as opposed to foraging or agriculture.
> Who is assuming?
Everyone, basically.
In the case of the Ashkenazi Jews, as far as we can tell they've been like that for as long as records of the group have existed. But the French Canadian specialization in commerce postdates the discovery of North America.