String theory is the only known theory that selects its own dimensionality. Se newton's laws can be in any dimension, but string theory cannot. Evolution has evolved our brain only to conceptualize in three dimensions. We cannot visualize a higher dimensional object easily because lions and tigers do not charge at us in five, six dimensions. Lions charge at us in three dimensions. And that's why evolution gave us a brain that can very easily conceptualize three dimensions. It was good for survival.