No one can for sure explain why humans living on the same planet as other animals are a lot more intelligent and no one can explain why there are unique human beings a lot more intelligent than others either!
It's very strange and there has to be something happening that can't be explained....do you believe in aliens,...I never did but now I do as a matter of fact I do believe they probably introduced intelligence to humanity!
It just does not make sense that people whether through evolution somehow became so intelligent that even their distant ape cousins are still that far off!... It's either alien did something to people or people traveled through time by wherever means and somehow their distant ape cousins are probably living in thousands of years behind!
Am a simple traveler that likes to get out and about from place to place,..but have you ever thought that as much as we think of cars or other physical means that we are also traveling through time!