Do the first two years of a childs life really determine his or her future development? Are human beings, like other primates, solely motivated by the pursuit of pleasure? What can be concluded today about the notion of temperament? Is it stable and unchanging throughout life? This book is the culmination of a lifetime of research. Jerome Kagan, one of the founders of modern development psychology, is known the world over for the precision and originality of his work, as well as for his overall examination of the methods and meaning of psychology. Jerome Kagan teaches at Harvard University. He is the author of several works on psychology that are regarded as classics.