Buss, Chapter 8 Problems of Kinship

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Buss, Chapter 8Problems of Kinship
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Hamiltons Rule

• Under what conditions will an altruistic gene
  spread in a population?
• c product of the benefit to the recipient X the
  degree of relatedness between actor and recipient

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Hamiltons Rule

• Examples for siblings or parents/children,
  benefit must at least double cost, as they are
  approximately .5 related for grandparents/grandch
  ildren, benefit must be 4X cost, as relatedness
  is about .25

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Hamiltons rule

• What does this rule NOT imply? That an
  individuals decision will be based just on this
  math!!
• Theory is that the formula determines when
  altruism can be expected to evolve
• However, patterns of helping CAN be predicted
  based on degree of relatedness

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Hamiltons rule

• Degrees of relatedness
• Siblings .5 half-siblings .25
• Parents/children .5
• Grandparents/grandchildren .25
• Cousins .125

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Altruism

• Ground squirrel studies alarm calls
• Predators kill more of those squirrels that give
  alarm calls compared to squirrels that do not
• Thus, giving alarm call is altruistic
• When do squirrels give alarm calls most reliably?

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Altruism

• Length of relationship did NOT predict
  probability of giving alarm thus, not reciprocal
  altruism
• Females give more alarm calls than males they
  are more likely to be surrounded by relatives
  than males are
• Even females who do not have offspring nearby
  still give alarm calls because of other
  relatives support for inclusive fitness
  hypothesis

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Altruism/helping

• Helping patterns in humans
• Number of helping instances correlates with
  degree of relationship (in study of women in LA)
• Type of helping relatively trivial vs.
  substantial
• Two main findings degree of relatedness
  predicted helping age of recipient also mattered

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Altruism/helping

• Age helping decreased, in general, with
  increasing age (thus decreasing reproductive
  value) of recipient, but only for substantial
  helping situations for more trivial helping,
  actually went up for old recipients

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Inheritance

• Inheritance and relatedness tend to leave more
  to close kin
• Leave more to offspring than to siblings, due to
  their greater reproductive value
• Male-female differences in wills men more
  likely to leave all to wives with no strings
  attached women often attach qualifications

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Inheritance

• Logic of sex differences likelihood of
  remarrying less for woman, so she is more likely
  to give mans assets to their children
• Man is more likely to remarry, and then give
  assets to new wife her children, so woman may
  be less inclined to leave him everything (and
  more likely to direct it to children instead of
  spouse)

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Inheritance

• Further support German studymen more likely to
  leave assets to wife if she was postreproductive
  than if younger (was a hypothetical questionnaire
  study) older wife less likely to remarry
  divert his assets to his nonrelatives

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Grandparents

• Paternity certainty joint probabilities
• Least certainty malesongrandchild (FaFa)
• Most certainty motherdaughter--grandchild
  (MoMo)
• Intermediate certainty mothersongrandchild
  (MoFa)
• Intermediate certainty fatherdaughtergrandchil
  d (FaMo)

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Grandparents

• Support for hypothesis dep. variablescloseness,
  time, knowledge, resources correlated with
  paternity certainty pattern
• Also, scores were higher for mothers father than
  for fathers mothermaybe because infidelity more
  common in younger generation than was case in
  grandparents generation

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Aunts uncles

• Similar pattern as for grandparents investing
  usually higher through maternal line (e.g.,
  siblings of mother) than through paternal line
  (siblings of father)
• Also found that aunts invest more than uncles, in
  general may be because uncles invest more
  resources in mating opportunities instead of
  descendents

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genealogy

• Females more knowledgeable about extended
  familycan name more relatives
• May be because family role was more central to
  womens success than for men