'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.
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
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
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.
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.