* Kiss of death for a high IQ is having ancestors that evolved in a tropical or subtropical environment.
You absolutely need severe winters to weed out the lesser lights, unmotivated, peeps with a “next week” at the most time horizon, and assorted other slackers.
When it’s mid 80s all the time, the lesser lights get along just fine and there’s no reason for any increase in IQ.
Sharks have had the same brain to body ratio for 400 million years, it’s all they needed to survive. The mutant sharks with big brains were no more successful than the average, so it was never incorporated as a desirable mutation….unlike humans along the 40th north parallel….