Intelligence: the ability to acquire knowledge, to think and reason effectively, and deal with the environment. Sir francis galton (england, 1869) influenced by darwin, argued mental ability is inherited. Attempted to measure efficiency of the nervous system related to mental skills (unfavoured & failed because they weren"t related) Alfred binet (france, early 1900"s) argued mental ability came with age & that mental competence remains constant with age. Developed intelligence tests mental age - age which an individual performs intellectually. William stern expanded mental age to develop intelligence quotient (iq) Iq = (mental age/chronical age) x 100: wasn"t accurate because of ages, increase in societys iq, deviation iq now used, intelligence test relative to scores of large. Stanford-binet test ( terman, 1920"s: mostly verbal items, produces a single iq score. Wechsler scales most widely used tests today in usa. Wechsler preschool and primary scale of intelligence.