Infidelity

1
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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2
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 a
  serious relationship (Shackelford et al, 2000)

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3
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-bonded mate

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4
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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5
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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6
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 than
  in male infidelity (Glass Wright, 1985)

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7
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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8
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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9
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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10
Infidelity Parental Investment
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11
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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