"The navigation of terrain on two unstable supports dependent on our balance and big toes and ability to account for gravitational pull? They all contribute to our abilities to read and do mathematics..."

Ostriches (which can do an Olympic marathon in 42 minutes!) are not great at mathematics. Humor aside, I agree with another commenter that human accomplishments, as compared with other animals, are often exaggerated. A gibbon can brachiate through the forest canopy (swinging and jumping from irregular branch to irregular branch) at the speed of a galloping horse. That involves far more dexterity than walking.