Sex differences in parental investment

Sex differences in parental investment

1. AO1

   • 'Any investment in an offspring that increases the chance that the offspring will survive at the expense of that parent's ability to invest in any other offspring' Trivers
     • Trivers believes females and males invest in offspring differently, females initial investment greater as gametes less numerous and more costly to produce than male gametes, and have to nourish kid for 9 months . Females can have limited number of kids, whereas males can have potentially unlimited
   • Limited offspring for females
     • 1. Breastfeeding last up to 4 years (some societies) 2. In UK & other western societies lasts between 3-12 months
   • Best way to maximise males reproductive success is to mate w/ as many partners as possible. Or, men need to concern themselves with fidelity of their mates so they can be sure she's mothering their kid.
     • Best way to maximise females reproductive success is to get best protection/ resources for her children
       • To be successful, you must pass on your genes. Means must have 2 babies who grow up to do same.

2. Sexual jealousy

   • Buss: asked P's to imagine their partner having sex/being in love w/ someone else and measured stress responses
     • Men more stressed at idea of them being unfaithful - therefore risks investing in offspring that aren't his
     • Women more stressed at idea of them being in love w/ someone else - Risked diversion of resources away from her and her family

3. Optimum level of offspring

   • Trivers argued that there is an optimum number of offspring for each parent.
     • Low investing male can afford many offspring, may favour 'quantity over quality'
     • Females would prefer quality rather than quantity. Consequently, females need to be much more choosey about whom they mate with

4. Maternal investment

   • Two consequences of the high cost of maternal investment: 1. Short term - men look for fertile women; women look for mate insurance. 2. Long term - men look for parenting skills and faithfulness; women look for resources, commitment and protection.

5. AO2/3

   • Inclusive empirical support: according to Daly and Wilson children under age of 2 at least 60x to be killed by step parent- mostly father - than by natural parent
     • Exactly what evolutionary theory would predict, since step- parents are genetically unrelated, whereas child inherits half of it's genes from biological parents
       • However most stepfathers don't kill or abuse, and a minority of biological fathers do: findings difficult to square with any explanation based on shared/non shared genes.
     • Trivers study in 1972 - family structures changed since then
   • how do evolutionary psychologists explain maternal neonaticide?
     • Pinker: when such act takes place in conditions of poverty, could be regarded as an adaptationist response. The psychological module that normally induces protectiveness in mothers in their newborns is switched off by challenge of poverty
       • Means both killing and protecting are explained by evolutionary selection.