text: Some people may be smarter than others because the may have more synaptic conections capable of reaching more neurons in many more parts of the brain. Having access to more "storage area" for memories, and being able to retreive more information from these areas. The resulting interconnectivity may produce a math genius, a gifted pianist, a soccer player, or a teacher or a physician. The first years in our life, under the care of our parents, our central nervous system is maturing. What happens then, may help explain your question. Loving, supporting parents, the absence of disease, and very good early education will create more synapsis.  Some of these characteristics may be of importance for the survival of the species, and will be coded in the DNA. So someone may be born smart, but without love and education early in life, may not be able to achieve its greatest potential.