PSY 544 Lecture Notes - Lecture 8: Ground Squirrel, Inclusive Fitness, Parental Investment
• The theory of parent-child conflict
• Schlomer et al. (2010)
• These researchers asked 11 to 14 yr old children to rate:
• Asked 236 11- to 14-year-old children to rate their level of conflict with their
mothers: so they asked to answer questions like: how much do you agree with the
statement that at least once a day you and your mother get angry with each other
o E.g., At least oe a da e get agr at eah other.
And they compared several groups:
• Compared several groups:
o Childre i itat failies other + father, ith ad ithout other full
siblings - Children in what they called intact families - so a mother and father
who have stayed together and have one or more children
o Childre i disrupted failies here the father has left, ith ad ithout
the entry of half-siblings into the home. So some of these families the father
has left and there's no half sibling in other families the father has left, another
man has come along and there's a half sibling
o Childre i disrupted failies, ith ad ithout the etr of a step-father
into the home. And then they also assessed the influence of having the
influence of step-father come into the home
• The weakness of this research is that it's a self report as they're asked children to
self-report how much conflict they experience with their mothers - the predication is
that when there are half-siblings in the home, because that creates a bigger
difference b/w the interests of the mother and the child, there should be more
conflict b/w the mother and child in homes with a half sibling vs homes with no half
sibling
• The theory of parent-child conflict
• Schlomer et al. (2010)
• We have the mean of the measure of the mother child conflict but it's standardized
around the mean for the entire sample so just means the avg amount of conflict for that
sample whereas any +ve value means more conflict than the avg for the whole sample so
what we see here is consistent with the theory that the levels of mother-child conflict
were higher in families in which half-sibling entered the home even compared to
disrupted families without half siblings - when the half-sibling enters the home we see
higher level of conflict in children and mothers than in disrupted families where the father
has left but no half-sibling has entered the home - this is consistent with the theory that
presence of half-sibling increases parent-child conflict.
• Another weakness is that the sample size is small
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•
• There is also data that is inconsistent with the theory of parent-child conflict in this
research - if you look at the intact families, remember that the theory of p-c conflict says
that any sibling ought to create conflict b/w what the parents want and what the kids
want because even with regular siblings there is conflict but if we look at the intact
families there is a lower level of p-c conflict with a full sibling (it's a negative value) - it's
inconsistent with the theory
• However, inconsistent with the theory, note that having a full sibling in the home did not
increase mother-child conflict!
• Consistent with the theory, levels of mother-child conflict were higher in families in which
a half-silig etered the hoe ee opared to disrupted failies without half-
siblings). But, note the very small sample size!
• P-C conflict theory is rarely tested and when it has been tested, findings aren't entirely
consistent with the theory
Extended family relationships: inclusive fitness and kin altruism
• Inclusive fitness
• The sorts of calculations we reviewed in discussing the theory of parent-child conflict
relate to inclusive fitness and can also be used to explain how kin altruism can evolve.
• Kin altruism is the idea that we are nicer to people who are genetically related to us than
people who are genetically unrelated to us. There are high levels of cooperation, you are
willing to incur cost to yourself to confer benefits to people who are genetically related to
you
• The way to read the diagram is that: you are related to yourself by 1 - any child: daughter
or son will be related to you by half. You have half of your parents genes (mother/father).
You have 25% of your grand parents genes (maternal and paternal genes). Because
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parents share half of their genes with their siblings and you share half of your parents'
genes, you share a quarter of your aunt and uncles genes. Your aunt and uncles share half
of their genes with their kids (and the other half of their partners genes) so you share with
your cousins 12.5% of your genes (25/2=12.5)
• The kin altruism hypothesis essentially says that All other things being equal, the closer
the genetic relatedness of a family member, the more that selection will favour
adaptations for helping them to survive and reproduce. So while talking about p-c conflict,
we said that genes that predispose you to be selfish but also to not be completely selfish
with respect to your siblings will survive more effectively than genes that promote you to
be completely selfish and ignore your sibling because your sibling is related to you and has
a chance of carrying those gene - so we can apply the same logic to the rest of our family -
so if there were genes that inclined you to confer survival and reproductive benefits to
your cousin, they would also survive and reproduce in the next generation - in this case
the amount of help that you should be promoted by your genes to give to your cousins
will be lower than it will be for your siblings or half-siblings -
•
• Inclusive Fitness
• Inclusive Fitness: is the idea that the extent to which you cause your genes to be
proliferated in the next generation is not just about your direct reproduction but also
what you do for your siblings survival and those who are genetically related to you so your
inclusive fitness is defined as your own reproductive success, plus the effects on the
reproductive success of your relatives weighted by their degree of relatedness and this
takes us to the Hamilton's rule
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Document Summary
But, note the very small sample size: p-c conflict theory is rarely tested and when it has been tested, findings aren"t entirely consistent with the theory. Extended family relationships: inclusive fitness and kin altruism. You have half of your parents genes (mother/father). You have 25% of your grand parents genes (maternal and paternal genes). Because parents share half of their genes with their siblings and you share half of your parents" genes, you share a quarter of your aunt and uncles genes. This is not a strict law, it doesnt not predict outcome 100% So when we talked about parent-child conflict we were using calculations of hamilton"s rules . So when you give the third portion of the food to your siblings that you could have consumed yourself, you incur a cost and the cost is -2 as that food would have benefitted you by 2 units.
