I have have had famous people ask me how the Ionian Greeks became so smart (in Classical times, natch). In Classical times, the Greeks – particularly the Ionian Greeks – gave everybody this impression – in everyday experience, and certainly in terms of production of outstanding intellects. Everybody thought so. Nobody said this about the Persians – and nobody said it about the Jews, who never said it about themselves.
It’s an interesting question: perhaps there was some process analogous to that which we have proposed as an explanation for the high intelligence of the Ashkenazi Jews. Or maybe something else happened – a different selective process, or maybe it was all cultural. It’s hard to know – the Greek Dark Ages, the long period of illiteracy after the fall of Mycenaean civilization, is poorly understood, certainly by me.
Suppose that your biological IQ capacity (in favorable conditions) is set by a few hundred or thousand SNPS, and that we have identified those SNPS. With luck, we might find enough skeletons with intact DNA to see if the Ionian Greeks really were smarter than the average bear, and how that changed over time.
More generally, we could see if civilization boosted or decreased IQ, in various situations. This could be a big part of the historical process – civilizations falling because average competence has dropped, science being born because the population is now ready for it…
I think we’ll be ready to try this in a year or two. The biggest problems will be political, since this approach would also predict results in existing populations – although that would probably not be very interesting, since we already know all those results.