Laboratory and sociological evidence indicates that the higher mammal may be psychologically at the mercy of his environment to a much greater degree than we have been accustomed to think. The greater the development of intelligence, the greater the vulnerability to emotional breakdown. The price of high intelligence is susceptibility to imagined dangers and unreasoning suspicion, and other emotional weaknesses. This conclusion is not only supported by work with animals but also agrees with the course of development in children, growing intelligence being accompanied by increased frequency and intensity of emotional problems up to the age of five years. Then, apparently, the trend is reversed. Adult