Charles Darwin, in "The expression of emotions in man and animals" (1872), showed that the way most emotions were shown was common between human cultures. He said this was inherited and had been the result of evolution. Behaviorism says that man's behaviour is affected by its results (operant conditioning). Behaviourists denied the importance of inherited behaviours, instincts, or an inherited tendency to behave. People who believe in evolutionary psychology think this is wrong. They think human behaviour has deep roots in our evolutionary past.