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Infidelity
Many human societies are based around
notionally monogamous relationships
However, it is relatively common for both
men and women to engage in sexual
activity with additional partners
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Infidelity
Prevalence of sexual infidelity difficult to
measure for obvious reasons. Some
estimates from the US:
Sexual infidelity occurs in 20-25% of
marriages (Wiederman, 1997)
65-75% of university students have had some
degree of extradyadic involvement whilst in aserious relationship (Shackelford et al, 2000)
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Infidelity
Infidelity also occurs in various animal
species, including those that apparently
form monogamous pair bonds
It occurs in both males and females
E.G. in some supposedly monogamous bird
species 10-40% of chicks were fathered by a
male other than the females pair-bondedmate
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Infidelity & Evolution
Infidelity might have evolutionary
advantages & be an adaptive strategy
If so, male & female infidelity are likely to
have different motives & possible
consequences
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Male Infidelity
Possibly explainable in terms of quantity
based indiscriminate mating strategy
More partners = more offspring
Men more likely to report having affairs that
were just about sex (Glass & Wright, 1985)
Male infidelity not necessarily linked to
dissatisfaction with current relationship (Hall &Fincham, 2005)
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Female Infidelity
Possibly explainable in terms of quality
based strategy for optimising survival
chances of offspring
Best physical specimens may not be best
resource providers (best of both worlds)
Infidelity more strongly linked to
dissatisfaction with currently relationship thanin male infidelity (Glass & Wright, 1985)
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Infidelity
That infidelity serves different purposes in
M & F is supported by other evidence e.g.
M less likely to forgive, more likely to break up
with sexually, rather than emotionally
unfaithful partner (Shackelford et al, 2002)
F seem more sensitive than M to emotional
infidelity (Hall & Fincham, 2004)
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Infidelity & Parental Investment
Infidelity may have an influence on
investment in offspring & other parental
behaviour
It makes poor evolutionary sense to invest in
offspring that dont carry your genes
Females can be certain that the young are
theirs, males less so Mummys babies, daddys maybes
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Infidelity & Parental Investment
Misattributed paternity prevalence is
difficult to measure. Sample estimates:
Anderson (2005) meta-analysis, studies of
general population: 3.9%
Bellis et al (2005) meta-analysis, studies of
general population: 3.7%
CSA (2005) cases of disputed paternity only:16%
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Infidelity & Parental Investment
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Infidelity & Parental Investment
Because females can always be certain
that the offspring carry their genes they
are likely to invest more resources
This tendency is multiplied across
generations, so mothers mother (guaranteed
relationship) invests more than fathers father
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