writing a summary There are two factors that 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 po matter how good a brain be has, to begin with, an individual will bave s low ordet of intelligence unless he has opportunities to learn. So the second factor is what happens to the individual-the sort of environment in which be is reared. If an individual is bandsapped ly, itis B yaat his brain will fail to deveep and he will never,tain level of the intelligence of which be is capable. The importance of environment in determining an individual's intelligence can be demonstrated by case hittory of the identical twins, Peter and Mark. Being identical, the twins bad identical brains at birth, and their growth processes were the same. When the twins were three months old, their parents died and they were placed in separate fostahomes. Peter was reared by parents of low intelligence in an isolated community with poor educational opportunities. Mark was reared in the home of well-to-do parents who had been to college. He was read to as a child, sent to good schools, and given very much opportunity to be stimulated intellectually. teens, when This tal difference continued until the twins were in their late they were given tests to measure their intelligence. Peter's LQ. was 85, well below the level he might have attained if reared under average conditions. Mark's LQ. was 125, twenty-five points above the average and fully forty points higher than his identical brother. Given equal opportunities, the twins, having identicalthin would have testedatroughly the same level.