I believe we evolved on the seashore and in the ocean. We have traits like, a film over our eyes, body fat over our muscles, like blubber, oils that coat the skin, partially webbed fingers and toes, sweat out salt, lack of fur, upright posture for standing in deeper water and swimming more streamline we can hold our breath for 3+ minutes. All these things are related to marine animals and not plains animals. No other large primate or any plains animal for that mater have these mutations.
Genetic drift is finite for example a black couple can never have a white baby but might have a lighter one who could have a lighter one and so on. A smart couple might have a smarter child and a drummer one but the smarter one has a better shot at a healthy long life with more offspring and multiple mates.
I believe a catastrophic change took place that destroyed the shore front environment we were evolving on and the only survivors of our species were the ones that moved inland in search of a better living and our intelligence is in direct portion to the intelligence of that group.