Overview
This lecture explores the biological, genetic, ecological, cultural, and evolutionary influences on aggression, competition, and cooperation, emphasizing the complexities of human violence and prosocial behaviors.
Perinatal Hormones and Aggression
- Early hormone exposure (especially androgens) can have organizational effects on brain structure, influencing later aggressive behavior.
- Animal studies show prenatal androgen exposure increases aggression in females.
- Human cases (e.g., congenital adrenal hyperplasia and diethylstilbestrol exposure) show ambiguous links between prenatal androgens and adult aggression.
- Twin studies suggest minor effects of prenatal testosterone on aggressive childhood play, but confounds make conclusions difficult.
- The "hyper-male" hypothesis of autism proposes prenatal androgens may contribute to autism, which is more common in males.
Genetics of Aggression
- Historically controversial, genetic factors now recognized as influencing aggression in animals and humans.
- Knockout or mutated genes can increase aggression, but often due to indirect effects like impulsivity or pain sensitivity.
- Solid candidates implicating serotonin and dopamine pathways.
- Gene effects depend heavily on early environmental factors (e.g., childhood abuse, stress).
- No simple gene predicts antisocial behavior; outcomes depend on context and upbringing.
- The XYY "supermale" hypothesis was debunked as an explanation for human violence.
Ecology and Culture
- Nomadic pastoralist cultures (e.g., herders) show higher rates of violence and value warrior classes due to defendable resources.
- "Cultures of honor" (e.g., in the American South) have heightened aggression in response to symbolic slights.
- Group violence correlates with myths of victimization and values of retribution.
- Ecological setting (deserts vs. rainforests) predicts patterns of violence and religious tendencies (monotheism vs. polytheism).
Social and Psychological Mechanisms
- Pseudo kinship: Groups can create bonds that mimic familial ties (e.g., military units), increasing cohesion and willingness to cooperate (or fight).
- Pseudospeciation: Making others seem non-human to justify aggression (e.g., propaganda).
- Us-them cognition can be triggered or reduced by experimental priming; perceiving others as individuals reduces amygdala-driven bias.
- Contact theory: Sustained intergroup contact can reduce aggression, but superficial exposure or poorly structured contact may increase hostility.
Evolutionary Perspectives
- Individual selection explains male-male violence over reproductive access and other forms of competition.
- Kin selection supports cooperation among relatives and explains some patterns of family violence but is not universally predictive.
- Reciprocal altruism and group selection foster cooperation when groups can punish cheaters, maintain reputations, or have repeated interactions.
- Group cohesion can both prevent internal violence and fuel external aggression (e.g., warfare, genocide).
Key Terms & Definitions
- Organizational Hormonal Effects — Early hormone actions that permanently shape neural circuits for future hormone responses.
- Activational Effects — Hormonal effects in adulthood that trigger specific behaviors based on prior organization.
- Pseudo Kinship — Socially constructed bonds that simulate family ties, enhancing group cooperation.
- Pseudospeciation — The psychological process of perceiving an outgroup as fundamentally different or non-human.
- Contact Theory — The idea that increased intergroup contact can reduce prejudice and aggression, under certain conditions.
- Cultures of Honor — Societies where reputation and honor are paramount, often leading to increased violence over symbolic issues.
Action Items / Next Steps
- Review game theory readings on altruistic and antisocial punishment (suggested, not required).
- Reflect on how cultural, ecological, and evolutionary forces shape social conflict and cooperation.
- Prepare for next lecture on further neurobiological or evolutionary mechanisms underlying social behavior.