Can Evolutionary Principles Explain Patterns of Family Violence? Archer, J. (2013). Can evolutionary principles explain patterns of family violence?. Psychological Bulletin, 139(2), 403-440. doi:10.1037/a0029114 Intro • “Violence within families is an extensive field of study whose research has wide-ranging implications for social policy” (Archer) • Focus on violence, subset of aggression • Application of evolutionary principles to research on family violence • Kin Selection – Adaptive for animals to distinguish kin from non kin Evolutionary Principles & Family Violence • Degree of shared kinship and Reproductive Value (RV) • Age, resources, and offspring quality • Resource Holding Power (RHP) • Characteristics of individuals engaged in conflicts Kin Selection • Kin are more likely than unrelated individuals to cooperate and less likely to compete, since altruistic behavior provides a way of perpetuating shared genes (W.D. Hamilton) • Inclusive Fitness • Parents care for offspring because they share genes that are rare in population • Hamilton’s Rule • Evolutionary costs and benefits • Benefits of helping a relative X coefficient of relatedness = costs • High rates of violence among step families • Kin Recognition • Animals must learn to differentiate kin • Assessment of the degree of resemblance • Facial resemblance = more cooperation and greater attraction Reproductive Value (RV) • RV is a measure of how likely individuals are to contribute to future generations • Offspring are more important to parents as a means of perpetuating genes than parents are to offspring • As offspring grow older, they become more valuable to parents • As parents grow older, their RV drops • Rates of violence • Offspring most at risk early in life, parents at risk the older they come Attachment & Selective Investment • Focus on offspring’s bond with his/her primary caretaker • Family violence • Attachment bond acts as an inhibitory influence on the motivational system underlying aggression Resource Holding Power (RHP) • Game theory model of the evolution of animal fighting (Parker, 1974) • Evaluating potential opponents fighting ability and act on information – fight or flee • Fighting ability = RHP • Assessing RHP and acting accordingly are an evolutionarily stable strategy (ESS; Maynard Smith, 1982) • RHP throughout the lifespan • Father son reversal of RHP Violence Between Parents, Offspring, and Siblings • Parental violence to unrelated Children • Reconstituted families are “crucibles for conflict” (Emlen, 1997) • Inclusive fitness • Degree of genetic relatedness • Higher rates of physical violence to children with stepparent across cultures • Higher risks from stepparents for homicide (Daly and Wilon, 1988) • Hostile rather than instrumental killings • Beating vs. suffocation, drowning, strangling, shooting, followed by suicide Violence between Parents, Offspring, and Siblings Cont. • Parental violence to genetic children • Parent offspring conflict model (Trivers, 1974) • Conflict will arise from offspring seeking more resources from parent • RVp • Reproductive value of parent decreases so parents value children more • Decline in parent abuse as parent grows older • RVc • Reproductive value of child is low early in life, but grows • Risk of abuse and neglect by parents higher for offspring’s early years, and then declines • Paternity Uncertainty • Facial resemblance Violence Between Parents, Offspring, and Siblings Cont. • Offspring’s Violence to Parents • As parents RV declines, offspring’s RV rises • Parents contribution to offspring’s fitness decreases • Parents RHP decreases as offspring’s RHP increases • Aggression to parents is frequent at young ages, but declines • Children express themselves physically, but learn to inhibit • Increase in offspring to parent homicide in 20’s • Increase in offspring RHP • More violence to stepfathers Violence Between Parents, Offspring, and Siblings Cont. • Violence Between Siblings • Inclusive Fitness • Predicts that genetic siblings will have less conflict than unrelated siblings • Confirmed in one study, more research is needed • Physical aggression is frequent between siblings, but generally at low levels • At young ages when aggression was common, older siblings showed more of it • RHP • Homicide most often occurs later in life between siblings • Greater tendency for siblings to cooperate and kill unrelated people Violence Between Partners • Partner violence as mate guarding • Paternity Uncertainty • Male doesn’t want to raise child that is not potentially his • Built in behavioral measures to maximize paternity certainty • Absence of sex difference in physical aggression to partners • Greater male – female violence found only in low gender empowerment nations • Findings support broader view – both sexes show mate guarding tendencies • Men want to avoid raising an unrelated child, women don’t want to lose a helper/protector Summary & Conclusions • Kin Selection • Greater risk of violence toward stepchildren than genetic children • Some parents showed abuse to stepchildren and not their genetic children • Weaker affective bonds with stepchildren • Reproductive Value (RV) • Violence by parents highest in infancy and decline through childhood • Supported for both violence and homicide • Supported by cues to poor physical prospects for child and shortage of resources • Decline in parental RV with age • Risk of violence to offspring declines • Risk of violence from offspring increases Summary and Conclusions Cont. • Resource Holding Power (RHP) • Older siblings generally initiate more physical aggression than younger ones • Boys moreso than girls • Sibling with lower RHP seeks help from parents • Reversal in parent-offspring violence in teenage years for boys • Partially supported • Increase in lethal violence in 20’s in case of sons to fathers Questions? • What are your thoughts on the research?