Is a notoriously difficult concept. It may be seen as a hierarchy of learning processes, with habituation , the most basic form of learning, being shared by all species. As we move ‘up’ the phylogenetic hierarchy, animals acquire the ability to learn by association ( classical and operant conditioning ), complex learning abilities such as problem-solving and learning sets, and finally, the acquisition of language (considered unique to humans).
However, this view of intelligence is criticised by many comparative psychologists as being unacceptably narrow. If intelligence is seen as the ability to solve problems that have ecological relevance in the animal’s own environment, then all species must be seen as equally intelligent in their own ways. There has been considerable comparative interest in species differences in self-recognition and theory of mind , although the relevance of such cognitive abilities to animals is still uncertain.
Intelligence may be simply a product of brain size, which present humans and the cetaceans (whales, dolphins and porpoises) as among the most intelligent species. Relative brain size (i.e. brain size relative to body size) is considered to be a better indicator of animal intelligence, although such a view also has problems (see brain size and intelligence ).
Intelligence may also be seen as a product of how animals solve social problems as well as physical problems, a form of intelligence that social psychologists call social cognition . Primates that form large and stable social groups are assumed to have the most highly developed social cognition of all animals. Repeated interactions over a prolonged period allow these animals to learn each other’s identities and to build up altruistic or antagonistic relationships. According to evolutionary psychologists, reasoning ability evolved largely out of the need to detect cheaters in social relationships (i.e. animals which take the benefits of social relationships must also pay a cost), a cognitive adaptation for social exchange .