The issue of the differences and similarities between humans and their cousins the chimpanzees governs the definition of human identity. How can this difference be explained? By studying the learning process of chimpanzees and comparing it to that of children, Ann and David Premack were gradually able to discover a series of differences, none of which were radical but when put together showed a yawning gap between the two species. The results they obtained enabled them to reconstruct little by little the sum of the differences that make up human identity. Ann and David Premack are specialists in the study of primates.