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Some time ago in West Africa, an extended warm period forced some apes out of the trees and onto the savannah, where walking erect probably allowed the brain to remain cooler (and gave certain advantages in predator early-warning). So human intelligence may have rapidly evolved as a consequence of a behavioral adaptation brought about by a sudden environmental shift.

Hmm. I was under the impression that the main reason for environmental pressure toward bipedalism was that the spread of the savannah favored animals that could see over the grasses and spot predators, hence the selective pressures in favor of bipedalism (but that's as much a conjecture as any other, I suppose). Intelligence, I thought, was more a byproduct of a shift to a high protein meat diet after the development of hunting skills that then allowed for the deveopment and maintenance of a larger brain.