PI = 'any investment that increases the chance child will survive at expense of parent's ability to invest in any other offspring - TRIVERS
Male & females dont invest equally --> Females not able to opt out of PI males can --> B/C males invest more courtship & can afford to devote little (in comp. to females) to parental care --> Adaptive value 4 unborn child = guaranteed caregiver (mum) --> Adaptive value 4 male continue to distribute genes elsewhere ..more offspring
Female gametes more costly than males = females only prod. 1-2 eggs per month, males limitless in prod. sperm --> Females invest more biologically than males, costs of childcare high --> Female ancestors min. maternal investment = 9month pregnancy, yrs feeding & carrying -->Min. paternal investment = teaspoon of semen --> Enormous diff. in max. reprod. success of sexes, random mating costly for human females --> CONTRADICTS PENTON-VOAK: females only mate w/males that are going to remain w/them --> Survey 2700 women .. 14% UK extra-marital mating --> Some women offset cost of PI by cuckoldry --> Extra-social support, better genetic quality --> H/W risks = abandonment & mate-retention strategies i.e. violence (Daly& Wilson)
Parental Investment II
Males need to ensure they arent cuckolded b/c human males considerable amount of investment in offspring & so greater concern about fidelity --> DUNBAR SUPPORTED males do invest parentally --> Males restrict reprod. opportunities to invest resources in children they believe are theirs --> Patriachal society .. adultery likely to be defined as what females 'did' --> I.E. Recent headlines= 'honour killings' Iran & Middle-Eastern countries
BUSS: US male students more concern sexual infidelity, female student emotional infidelity --> Physiological responses (heart-rate/BP increase) = males more distress imagining sexual imagery .. CHALLENGES view sex diff. in jel.are adaptive response in males & females --> METHODOLOGY: scientifically objective (replicable & reliable) --> H/W sample used ..generalisability..students high rate IQ.. younger .. less likely to maintain long-term relationship
CLOSELY RELATED SPECIES = Chimpanzees & Bonobos -> in both species males little/no parental invstment --> suggests emergence of male parenting in humans dramatic evolutionary change over primate ancestors/contribution of cultural learningExplana. of PI based evolutionary factors alone REDUCTIONIST --> Men's parental behaviour depends personal & social conditions inc. quality of relationship ..
..w/mother, characteristics of child, personality of father -> Childhood experiences may also affect upbringing of their child
PI theory males dont want anything to do w/offspring that arent theirs --> H/W ANDERSON CONTRADICTS = no diff. in resource allocation b/twn step-children & their biological offspring --> CULTURAL DIFF? Wstrn economies vs. 'poorer economies' = availability of resources to 'waste'