Eliezer: human development looks to me like a poor source for insights on general intelligence. Consider the many human traits - hunting, tools, clothing, fire - that pre-date any hint of generality and ought really to be considered instinct. Consider that behavioral modernity is something like 50 kiloyears old, anatomically modern humans existed without a hint of culture for about 150 kiloyears before that point, and some isolated groups of anatomically modern, cultured, talking, music-making humans remained stuck in the stone age until the 1960s. Also, consider how few car-driving humans can perform the math that defines their car. It's evident to me that we are so very marginally generally intelligent as a species, that you would be hard put to nail down the signal amongst the noise.