there are two factors the determine an individual's intelligence. The first is the sort of brain he is born with. Human brains differ considerably, some being more capable than others. But no matter how good a brain he has, to being with, an individual will have a low order of intelligence unless he has opportunities to learn. So the second fไactor is what happens to the environmentally, it is likely that his brain will fail to develop and he will never attain the level of intelligence of which he is capable.