Evolutionary forensic psychology perspectives Presented By: Joseph A. Camilleri Evolutionary Psychology November 8 th, 2002

Definitions Homicide –Killing of one human being by another Neonaticide –Killing of an infant within 24 hours after his/her birth Infanticide –Killing of an infant within 1 year after his/her birth Filicide –Killing of a son/daughter over the age of 1 Uxoricide –Killing of the wife by a husband Parricide –Killing one’s parent

Why study homicide? Conflict assay (Daly & Wilson) –Window on evolved motivations that are rarely lethal Severe and genuine conflict –Unlike self-report Minimal biases of detection & reporting

Adaptive or Non-Adaptive Byproduct? Homicide is rare Non-Adaptive Byproduct 1.Male competition 2.Discriminative parental solicitude 3.Sexual jealousy/proprietariness

Who are the victims of homicide? 13 th Century England Homicide Data Victims are rarely related to the offender Co-offenders are more likely to be genetically related (Daly & Wilson, 1988)

Cross-cultural data Daly & Wilson (1988) Homicide

Who does the killing? Daly & Wilson (1990) Human Nature 1:

Most common situation… Men killing men Motives… Majority of all homicides (37%) are “altercations of relatively trivial origin; insult, curse, jostling etc” (Wolfgang, 1958) “Altercations appeared to be the primary motivating forces… usually trivial, indicating that many homicides are spontaneous acts of passion” (Mulvihill, Tumin & Curtis, 1969)

Most common situation continued… Maladaptive By-product #1: Competition –Females are choosey –Look for dominant male –Insults focus on one’s dominance (weak, poor…) –Violence is an adaptive way of deterring/resolving Examples… Movie Duels –Men willing to die for honour ‘Chicken’ –Car race to edge of cliff

Most common situation continued… Generally, violent behaviour is related to fitness and lethality may be governed by situation –Less secure society, homicide may be seen as ‘adaptive’ eg Dani Tribe, ‘kepu’ –Some groups, killing is a primary method of survival eg Mafia –Variance of income

Familicide RelationshipPercent Unrelated acquaintances 48% Stranger27% Relatives25% RelationshipPercent Consanguinal25% Spouse63% In-laws8% Step children4% All homicides: Detroit 1972Killing relatives: Detroit 1972 * 75% of all familial homicides were directed against non-genetic kin

Uxoricide Two possible theories 1.Risk increases with age -Due to less value 2.Risk decreases with age -Younger, more valuable mate increases jealousy/proprietary

Uxoricide continued… The winner is… Risk decreases with age Wilson & Daly (1998) in Rethinking Violence against Women (Dobash & Dobash, eds.)

Uxoricide continued… Maladaptive By-product #2: Sexual Proprietariness (Daly & Wilson) Males guard and control a valuable mate Males will change efforts due to… –Factors affecting her mate value (youth, health) –Factors affecting his mate value (status, resources) –Competition (sex ratio and qualities of rivals)

Uxoricide continued… Factors affecting his mate value & competition Study by Dijkstra & Buunk (1998) –Males are influenced by a rival’s dominance –More dominant rivals evoke greater sense of jealousy –These types of responses may be adaptive, but lethal consequences are not

Uxoricide continued… Potential confound #1? Coincides with age of males that murder more often… –NO: Risk is elevated with older husbands Age specific rates of killing same sex unrelated persons Uxoricide rates for wives aged years Homicides per million Daly & Wilson (1999) Scientific American Presents 10(2): 8-14

Uxoricide continued… Does presence of step children increase uxoricide risk? –YES: Evidence for greater shelter admissions and uxoricides with presence of step-children (Daly & Wilson) Uxoricides ( ) Daly et al Homicide Studies 1: Genetic Mixed Step only only Shelter admissions ( ) per 1000 per annum Genetic Mixed Step only only

Neonaticide, Infanticide & Filicide Who is at most risk? 1.Stepchildren: Child’s age (years)Canada Homicides per million

Filicide continued… Maladaptive by-product #3: Discriminative Parental Solicitude *Remember, step-parental homicide is RARE, however, presence of a step-parent increases a child’s risk by over 100% Makes sense to invest more with children who are genetically related –Spend less $ per child on food –Less financial support for college

Filicide continued… Who is at most risk? 2.Younger children Per capita rates of validated child abuse reports to the American Humane Association, 1976 Wilson et al (1980) J Biosocial Science 12:

Filicide continued… Who is at most risk? 3.Children with younger mothers England & Wales Ayoreo: Mid- 20 th Centruy Canada:

Filicide continued… Maladaptive by-product #4: Residual reproductive value - the older the mother the lower the opportunity cost

Summary Definitions Conflict assay Adaptive vs Non-adaptive byproduct –Male competition –Sexual proprietariness –Discriminative parental solicitude –Residual reproductive value Homicide perpetrators/victims –Homicide, uxoricide, filicide