According to Galton, the highest IQ people ever were the Athenians. Their contemporaries agreed. Athens of Pericles (pic) was the cutting edge of human culture. Athens' alter ego was Sparta, its black twin separated at birth: they measured up each other in a terrible 28 year Peloponnesian war, and Sparta emerged superior.
Spartans were of the Dorian race, tall and slim and Nordic-looking. Originally they lived in four agricultural villages in the high Eurotas river valley when somewhere in the Greek Dark Ages they held an assembly and decided to give up subsistence farming and appropriate the surplus production of the Messenians living on the other side of the mountain. The Messenians were Dorians like themselves, and they were many: 200 to 400 thousand, against Sparta's 10 to 20 thousand. So they carefully organized themselves for this ambitious project.
Each Spartan gave up his land and gold, and they formed themselves in regiments. They stopped eating with their families and established communal messes, each one contributing food. They organized intensive military training, use of weapons and experimented with battle formations. They established the agoge, a comprehensive war school till age twenty when they were recruited into regular regiments. For almost a generation they fought the Messenians, till they conquered them and divided the land among the
homoioi (the similars, that is, "pure" Spartans that completed the agoge and had been accepted in a mess as equals).
To maintain the Messenians submissive, they created murderous Cryptic Patrols that systematically culled off the stronger-looking peasants. It was not conceptualized as a dysgenic/dumbing down program of the enslaved population, only as precautionary policing.
Being in campaign most of the time, they got a taste for male love and failed to care for families. Men being away campaigning, the women managed the farm. Eventually, Sparta learnt the business of war so well that conquered whole Greece.
They only neglected to reproduce themselves. There was no way to make young warriors to marry. The commune imposed fines and public shaming, but no children were a-coming. They would not accept non-Spartans, they would not share their wealth and power with strangers. At the peak of their power, no more than 3 or 4 thousand full Spartan citizens were left, lording over a Greece of 5 million.
When Alexander descended from Makedonia, the Spartans could not muster opposition for lackof manpower. Sparta was depopulated and abandoned, it became a tourist attraction, like say Venice today, with its North African gondoliers singing as tour guides.
My conclusion is that high IQ is unsustainable, it is poison. Eugenic societies don't last. The more I think about it, the more convinced I am that Pericles' open, liberal democracy is superior (*).
It is a paradox because rationally, it should not be so, but the fact is that it is so.
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(*) Note that its "openness" was strictly limited. Athens was an ethnic refuge or sanctuary in the extreme Southern corner of the Greek peninsula, surrounded by Dorian peoples like the Boiotians that applied a permanent pressure to drive them into the sea. Almost all the Ionians migrated to the isles and to Asia Minor, and only Athens remained as the last Ionic settlement on the mainland. Not less racist than the Spartans, Athenians had a multilayer procedure to establish the genealogy of the ephebes (18 y.o.) applying for military service and full citizenship. Those founded of mixed blood were sold as slaves.