Evolutionary Psychology & Aggressive Behavior

Evolutionary psychology is a relatively new branch within the behavioral sciences, having formal underpinnings beginning in the 1970s. While Darwin offered the basis for evolutionary psychology in his theory of evolution, he largely focused on biological adaptations resulting from evolutionary pressures. Evolutionary theory, in parallel, addresses psychological adaptations such as language, sexual selection and aggression.

Aggression, as a psychological behavior, is an act intended to cause physical, mental or social harm, particularly between members of the same species. While we often think of aggressive behavior as physical violence, psychologists also consider instances of a more subtle nature. For example, using rumor to damage another's reputation and public ridicule are both forms of social aggression.

In-Group Aggression

• In-group and same species aggression is considered a component and tool central to social networking and status determination. Robert Wright, in his book "The Moral Animal," describes our tools for social climbing as, "aimed either at kin, who share our genes, at non-kin of the opposite sex who can help package our genes for shipment to the next generation, or at non-kin of either sex who seem likely to return the favor."

  Those who cannot or will not meet these criteria are often met with increasing levels of aggression, sometimes to prevent others from altering an individual's current status, at other times to remove or capture the social status of an opponent.

Out-Group Aggression

• Survival is a primary source of aggression between members of different species. It is also viewed as a source for cooperative and altruistic behavior between those of the same species, resulting in behaviors such as herd mentality and the apparently selfless act of sacrificing oneself in defense of others.

  The psychology of out-group aggression also explains interactions between members of the same species found within different subgroups, real or imagined. For example, racism and warfare may be partially understood through the same psychological components that govern out-group aggression, founded on instincts for survival and preservation of resources.

Aggression and Altruism

• Altruism is often thought of as an individual's cultural and social selflessness. Evolutionary theory, however, describes it as a system of behaviors that may not appear to directly benefit the altruistic individual, yet, in reality, aid in an evolutionary sense.

  Robert Trivers, in his 1971 paper "The Evolution of Reciprocal Altruism," outlined aggression as one of many "important adaptations to regulate the altruistic system." It accomplishes this by persuading others toward mutually profitable social behavior.

  For example, Wright explains, "If word of your fierce honor gets around, so that a single, bloody fistfight deters scores of neighbors from cheating you--even slightly and occasionally--then the fight was worth the risk." The result is a reciprocal altruism, wherein each participant respects the honor of others, held in check through implied and actual aggression.

Gender Aggression

• Evolutionary psychology predicts different styles of aggression based on gender, particularly as they relate to sexual roles. In most cases, males tend toward direct aggression and physical violence, while females are apt to engage in more social and indirect forms. These differences are explained primarily as a result of gender-based, sexual investment.

Sexual Selection and Investment

• Typically, males may generate numerous offspring based on the number of females with which they have sexual access. Male aggression therefore benefits an individual by limiting and thwarting the sexual access of other males to the available pool of females.

  Females, by contrast, have a much higher investment in reproduction. Individually, a female may produce a limited number of offspring at any time. As a result, females benefit by mating with the strongest and most resourceful males, and success often requires social, rather than physical, aggression.