To state whether intelligence is absolutely hereditary or environmental is pure retarded. Firstly, people would readily accept that there are biological predispositions to some physical features (height, looks, hair,) as well as some mental disorders, so why exclude intelligence? You would find a great sum of literature dealing with the hereditary of intelligence which explains it far better than I ever would. Look it at from this perspective. Intelligence can be likened to the baking of a pizza. One's natural abilities would be set as the base and the environmental factors act as the topping. One cannot exist without the other and the finished product is dependant on the quality of both ingredients.