The concept of the evolution of morality refers to the emergence of human moral behavior over the course of human evolution. Morality can be defined as a system of ideas about right and wrong conduct. In everyday life, morality is typically associated with human behavior rather than animal behavior. The emerging fields of evolutionary biology, and in particular evolutionary psychology, have argued that, despite the complexity of human social behaviors, the precursors of human morality can be traced to the behaviors of many other social animals. Sociobiological explanations of human behavior remain controversial. Social scientists have traditionally viewed morality as a construct, and thus as culturally relative, although others such as Sam Harris argue that there is an objective science of morality.
Some evolutionary biologists and game theorists argue that since gradual evolutionary models of morality require incremental evolution of altruism in populations where egoism and cruelty initially reigned, any sense of occasional altruism from otherwise egoistic and cruel individuals being worse than consistent cruelty would have made evolution of morality impossible due to early stages of moral evolution being selected against by such sentiments causing the individuals with some morality to be treated worse than those with no morality. This would have caused low degree morality to become an adaptive valley that would preclude the early steps away from the no morality condition, precluding an early necessary condition for later evolution of higher degrees of morality. These scientists argue that while this rules out evolutionary explanations of the specific type of morality that feels disgust at some empathy from rarely empathic individuals by assuming it to be psychopathic Machiavellianism, it does not rule out evolution of other types of morality that accept a little altruism as better than no altruism at all.
While groups may benefit from avoiding certain behaviors, those harmful behaviors have the same effect regardless of whether the offending individuals are aware of them or not. Since the individuals themselves can increase their reproductive success by doing many of them, any characteristics that entail impunity are positively selected by evolution. Specifically punishing individuals aware of their breach of rules would select against the ability to be aware of it, precluding any coevolution of both conscious choice and a sense of it being the basis for moral and penal liability in the same species.
See also: Evolutionary origin of religions
Psychologist Matt J. Rossano muses that religion emerged after morality and built upon morality by expanding the social scrutiny of individual behavior to include supernatural agents. By including ever watchful ancestors, spirits and gods in the social realm, humans discovered an effective strategy for restraining selfishness and building more cooperative groups. The adaptive value of religion would have enhanced group survival.
See also: Evolution of human intelligence § Social exchange theory, Evolution of human intelligence § Sexual selection, Prisoner's dilemma, Sexual selection in humans, Altruism (biology), Cheating (biology), Mate choice, Sexual jealousy, Seduction § Human mate poaching, and Mate guarding in humans
In an experiment where subjects must demonstrate abstract, complex reasoning, researchers have found that humans (as has been seen in other animals) have a strong innate ability to reason about social exchanges. This ability is believed to be intuitive, since the logical rules do not seem to be accessible to the individuals for use in situations without moral overtones.
Disgust, one of the basic emotions, may have an important role in certain forms of morality. Disgust is argued to be a specific response to certain things or behaviors that are dangerous or undesirable from an evolutionary perspective. One example is things that increase the risk of an infectious disease such as spoiled foods, dead bodies, other forms of microbiological decomposition, a physical appearance suggesting sickness or poor hygiene, and various body fluids such as feces, vomit, phlegm, and blood. Another example is disgust against evolutionary disadvantageous mating such as incest (the incest taboo) or unwanted sexual advances. Still another example are behaviors that may threaten group cohesion or cooperation such as cheating, lying, and stealing. MRI studies have found that such situations activate areas in the brain associated with disgust.