心の理論
Primates have advanced cognitive abilities: some make tools and use them to acquire food and for social displays; some can perform tasks requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can recognise [[Kinship|kin]] and [[conspecific]]s; and they can learn to use symbols and understand aspects of human language including some relational syntax and concepts of number and numerical sequence. Research in primate cognition explores problem solving, memory, social interaction, a [[Theory of mind#Non-human|theory of mind]], and numerical, spatial, and abstract concepts. Comparative studies show a trend towards higher intelligence going from prosimians to New World monkeys to Old World monkeys, and significantly higher average cognitive abilities in the great apes. However, there is a great deal of variation in each group (e.g., among New World monkeys, both [[spider monkey|spider]] and [[capuchin monkey]]s have scored highly by some measures), as well as in the results of different studies.