Who Determines Intellectual Capacity?

How is the intellectual capacity of an individual is determined? I would have to say that the brain is one of the most unique organ that function on your body. The brain is designed to store a gargantuan amount of memory; therefore, who knows the maximum amount an individual could actually retain and store. There are many things that we should focus on in life and the main thing I feel that should be, as far as intellectual capacity, is educating yourself beyond the imaginable.