Why Humans Are Unique: Three Theories.

Three recent papers reject Darwin's claim that there is no fundamental difference between humans and animals. Each offers a unique theory of the difference. The first theory holds that although animals can perceive perceptual relations, humans alone can reinterpret the higher order relations between these relations. The theory offers analogical reasoning as an example of the uniquely human ability to deal with higher order relations between relations. However, chimpanzees are capable of analogical reasoning if the analogies are conceptually simple. The second theory proposes that human intelligence has far better developed social than physical competence-a claim that ignores, and is contradicted by 20 years of infant research showing that the infant's social and physical modules are almost equally developed. The third theory finds that whereas animal abilities are limited adaptations restricted to a single goal, human abilities are domain general and serve indeterminately many goals. This article rejects the first two theories and explains the unique character of domain-general human competence in terms of the interweaving of evolutionarily independent abilities-an interweaving found in humans only.