I recently watched a documentary on "feral children", (wild children). While these children can learn to some degree, MRI's and CT scans show marked damage to the brain, areas that never developed because of lack of use. This is permanent damage. Therefore (IMHO) Intelligence has as much to do with nurture as with nature. If parts of the brain are not stimulated they fail to develope the necesary nueron connections to use them. Interesting stuff.