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Inclusive Fitness
Psychology 3107
Introduction
Darwin was troubled by the
preponderance of behaviour that seemed
to be of no benefit to the actor
Examples
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Sterile insect castes
Bee stings
Alarm calling
Reproductive restraint
Reproductive restraint
Birds can produce
many more eggs than
they actually do!
Wynne-Edwards
beleied that selection
also acted on the
species level to stop
massive
overpopulation
Reproductive Restraint?
Lack argued that animals
are doing what is best for
the INDIVIDUAL
Big clutch means
possible exhaustion,
death
LIFETIME fitness, not just
this season
Lack
Well, if clutch size
depends on the
environment, then
clutch size should
vary with quality of
resources
Hamilton figured it out
Hamilton’s Response
was theoretical
Look at behaviour
from the gene’s point
of view
Inclusive fitness =
direct fitness + effect
on fitness of others
Hamilton
C < rb
Or r > c / b
Remember, r is relatedness, c is cost b is
benefit
Would you give your life for a brother?
No, but maybe 2 brothers, or 8 cousins
Two uncles and one mother….
Mechanism
For this to work there must be some sort
of proximate mechanism
Easy for mother/father and child
How about everyone else?
‘Green Beard’ hypothesis
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Allele produces some phenotype
Also allows for recognition
Tough for a single gene….
The elusive mechanism
Proximity
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Families
Little dispersal
So if close by, you are related
Example:
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Leaf eating ants
Far nests  more hostile
Different plants  more hostile
More on mechanism
Those crazy ants
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Split colony and put on different plants
Hostile, but non injurious!
Gene environment interaction baby!
Vervet monkeys
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2 year olds scream
Mother comes
Others watch the mother!
Mechanisms, pheremones and
bees
Greenberg looked at
bee relatedness and
allowing bees in or
not
Probably genetically
determined odour
Conclusions
Group selection is silly
Individual selection is cool
Gene level selection is VERY cool
Hamilton is a genius
Don’t over use this
Gives us some insight into some nasty
human behaviour