e second half of the twentieth century to move away from the extreme scepticism and behaviourism of the first half. Elaborate and painstaking laboratory testing has added weight to theories which presume that psychological capacities under the headings of perception, expectancy, emotion and memory are present in at least the higher vertebrates, the mammals and birds. Specialized experimentation with monkeys and chimpanzees has confirmed that intellectual abilities of some description are present in these species, although attempts to train chimpanzees in the social and syntactical complexities of human language have had successes so limited that they would be better called failures.
Animals are widely used for investigating physiological mechanisms rather than psychological theories: for instance, for investigating the details of the eye and brain which allow for vision, or for studying the brain biochemistry which accounts for the emotional effects of tranquillizing or addictive drugs. For this and other reasons an important comparison in comparative psychology is between the human species and the rest. It was Aristotle's view that perception, memory, passion, appetite and desire, as well as pleasure and pain, belong to almost all living creatures. Modern studies would place greater restrictions on the generality of these psychological components, but for a full understanding of human youth and age, sleep and dreams, and human passion and perception, biological comparisons remain essential.
S. F. Walker Birkbeck College, University of London
McFarland, D. (ed.) (1980), The Oxford Companion to Animal Behaviour, Oxford.
Walker, S. F. (1983), Animal Thought, London.
See also: ethology; evolution; instinct; sociobiology.