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Lecture 18

PSYC 3100 Lecture Notes - Lecture 18: Sibling Rivalry, Parental Investment, Intragenomic Conflict


Department
Psychology
Course Code
PSYC 3100
Professor
Pat Barclay
Lecture
18

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Evolutionary Psychology Lecture 18 Family Conflict
Parent/Offspring Conflict
Parent/ offspring conflict is even found in plants (between parent and seed; investment
in that seed and other seeds)
Why expect conflict?
o In evolutionary term, families are collections of individuals who share many
genes by common descent. Because of their genetic overlap, they also have
overlapping evolutionary interests. But because a family’s members are not
genetically identical, they are bound to disagree to some extent
o Thus, evolutionary thinking suggests that we should expect a certain amount of
conflict in families for the simple reason that each individual’s own fitness
interests inevitably conflict to some degree with those of others in the family
o The fundamental reason for conflict in the family is that each individual is related
to himself or herself more closely to anyone else
Trail Marker evolutionary theory predicts both cooperation and conflict among kin
Sibling rivalry:
o Relatedness to self: 1.0
o Relatedness to sibling: 0.5
o Relatedness to offspring: 0.5
o Relatedness to niece/nephew: 0.25
Parent-offspring conflict:
o A parent’s r to each offspring is 0.5
Therefore, all offspring are genetically valued equal
Offspring value themselves more than their siblings
Parent-offspring conflict revolves around the optimal distribution of that
investment
Parents prefer equal investment in offspring, but each offspring benefits
from getting slightly more parental investment than their siblings
Each offspring wants slightly more than the parent is willing to
give
Mom faces a choice: should she invest it in her current offspring or
should she invest in her next offspring
All of a mother’s offspring will equally carry one half of her genes,
no more, no less
All are therefore equally valuable in terms of their ability to
spread her genes, so she will favor an equal distribution of
investment among her children
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