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Slide 1

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Sex Differences in
Parental Investment
Relationships ­ Topic 5…read more

Slide 2

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What is parental investment?
Trivers (1992)
Parental investment is any investment by a parent in an
offspring that increases the chance that he offspring will
survive at the expense of that parents ability to invest in
any other offspring…read more

Slide 3

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Maternal Investment AO1
· The investment made by human females is considerably greater than
that made by males.
· This is because women produce less eggs in their lifetime than males do sperm
· Also, females can always be certain they're the mother (unlike fathers)
Why do human females invest
What are the costs of maternal
· As brain size increased as a result
· Symons (1979) explains that for our
of adaptation, human skull size
also increased
· The minimum maternal investment
· As a consequence, human
for females is 9 months of pregnancy
childbirth occurs earlier in
and years of feeding and carrying
development than other animals
· The minimum paternal investment is
· Human females have to breastfeed
a few moments of copulation and a
their young which means they're
teaspoon of semen
burdened by their child's extended
· This makes random mating much
period of child care
more costly for females
· Therefore, females contribute
more both during pregnancy and
post pregnancy…read more

Slide 4

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Extra Marital Affairs AO2
· The result of women's high parental investment is illustrated by
Baker and Bellis (1990)
· Due to high maternal investment, females want to ensure high
quality offspring
· They may do this by marrying a caring man with resources but by
finding good genes from elsewhere through extra marital affairs
· They support this with the estimation that 14% of the population
being products of extra marital affairs
This supports the idea that maternal investment is higher than paternal investment
and also suggests the consequences of this.…read more

Slide 5

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The benefits and risks of cuckoldryAO2
· Another consequence of women's high parental investment is that
some women may try to cuckold their partners
· This could benefit women by providing additional social support
from a second male and may also provide superior genes
· This suggests that cuckolding benefits women
However... The female could be abandoned or threatened by violence against her by
their partner…read more

Slide 6

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Paternal Investment AO1
· The investment made by human males is considerably less than that
made by females.
· This is because women produce less eggs in their lifetime than males do sperm
· Also, males can simply walk away after fertilisation which makes random mating
less costly for males
Sexual and emotional jealousy
Paternal investment and cuckoldry · The possibility of sexual infidelity is more
· When males invest their resources of a risk for a male as he could end up
they're under pressure to protect investing in offspring that isn't his own
themselves from investing in · Whereas for a female who's mate is
offspring that aren't their own unfaithful resources could be diverted
· Miller (1998) ­ as human males away from her and her offspring
make a considerable investment in · Buss (1995)
their children they have more · Sexual jealousy may have evolved as
concern about their mates fidelity a solution to these problems
· As a result, they try to ensure that · Men are more jealous of the sexual
their care isn't misdirected to non- act in order to avoid cuckoldry
relatives · Women are more jealous of
emotional infidelity in order to avoid
losing resources…read more

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