There are two aspects which determine an individual’s intelligence. The first is the brain he is born (26) . Human brains differ considerably, (27) being more able than others. (28) no matter how good a brain he has to begin with, an individual Will have a low order of intelligence (29) he has opportunities to learn. So the second aspect is what (30) to the individual — the environment in which he is brought (31) . If an individual is handicapped (32) , it is likely that his brain will (33) to develop and he will (34) attain the level of intelligence of which he is (35) . The importance of environment in determining an individual’s intelligence can be (36) by the case history of the identical twins, Tom and Mike. When the twins were three months old, their parents died, and they were placed in (37) foster homes. Ton, was reared by parents of low intelligence in an (38) community with poor educational (39) . Mike, (40) was educated in the home of well-to-do parents who had been to college. This environmental (41) continued until the twins were (42) their late teens, (43) they were given test to (44) their intelligence. Mike’s I. Q. was 125, twenty-five points higher than the (45) and fully forty points higher than his identical brother.

26().