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Anth 562

Sociobiology
by

Charles Snyder

on 18 February 2011

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Transcript of Anth 562

Anth 562 2/18/2011 Our Authors William Donald Hamilton (1936-2000)
British evolutionary biologist
Extensive work on kin selection and altruism
Hamilton's Rule Alan Grafen
Scottish evolutionary biologist
Student of Richard Dawkins
Extensive work on game theory Robert Trivers
American evolutionary biologist/ sociobiologist
Known for work on reciprocal altruism,parental investment, and parent-offspring conflict Robert Axelrod
American Professor of Political Science and Public Policy
Works on the evolution of cooperation Trusting in the Process Phenotypic Gambit
The implicit assumption that phenotypic patterns are good predictors of genetics.
Has proven to be valid for traits with high heritability
Is controversial for traits with low heritability Why focus on the gambit? Without the gambit:
Studies on the nature of a character as an adaptation would be required to include a study on the underlying genetics.
This would be time and resource intensive
In some cases, this type of study would be impossible Inclusive Fitness "...a device that simplifies the calculations of conditions for the spread of certain alleles. These alleles have an effect, through their bearer's phenotype, on how many offspring other animals in the population produce." (Grafen p.66)

Simply Put: Classical fitness + the number of offspring equivalents (weighted by relatedness) it adds to the population by helping/supporting others. Altruism: Dictionary: Behavior by an animal that may be to its disadvantage but that benefits others of its kind.

This definition may be limiting Altruism and the Degree of Relatedness
Hamilton (1964) shows that degree of relatedness is an important predictor of how selection will operate.
Has a direct (self) component and an indirect component
Is it really altruistic? Kin Selection Drowning and Degree of Relatedness
You are at the river when your sister and your cousin fall in.
You can only save one.
Who do you save?

Your full sibling has half your genes in common so r=.5
Your cousin has about 1/8 of your genes in common r=.125
Hamiltons Rule and Kin Selection
rB>C Drowning revisited
rB>C or rB-C>0
r=Degree of Relatedness
B= The additional reproductive benefit gained by the recipient.
C= The reproductive cost to the performer (can be effected by several elements such as age, reproductive future etc.)
If you save anyone, you are likely to save your sister THis is a small word Examples: Superb Blue Wren
Helping at the nest
Helpers increase production
B=Benifit to parents as difference helper made
C= cost to juvenile as the average number of offspring preduced by unhelped pair Additional Considerations
C can be situational
For females C= 1.5
For males that find mates C=1.5
For males that do not find mates C= 0 Conclusion
Pairs with helpers have 2.83 offpsring (average)
Pairs W/O helpers have 1.5
The difference between with and W/O, B= 1.33
Females: 1.33-1.5= -0.17
Males with mates are the same.
Males without mates: 1.33-0= 1.33 Reciprocal Altruism Increasing one's own fitness through altruistic acts with the expectation of being repaid in the future. Can occur whether the individuals are genetically related or not.
Can cross species boundaries
Has time lag between act and benefit Examples:
Cleaning Symbioses
Rules for Kin Selection:
Must have:
Lifetime long enough to realize benefits
Low dispersal rate
Mutual Dependence Warning Calls in Birds Vampire Bats Some perameters for selection favoring reciprocal altruism:
Long enough life to benefit
The benefit that accrues must be greater than the accrued cost
Must be enough interaction to sustain reciprocity
Individuals able to detect cheaters Tiger Salamanders
Salamaders were raised in groups of:
Full sib
Half sib
Unrelated
Full sibs eaten least, Unrelated eaten most
This suggests that relatedness is somehow known Prisoner's Dilemma
Two participants may not cooperate despite the fact that it is in their best interest. Two crimials are arrested on suspicion of commiting a crime
The police do not have enough evidence to fully convict them both
The prisoners are isolated and visited by police offering a deal: Offer evidence against the other and one will be freed.
If neither accepts, both get minimum punishment due to lack of evidence
If one accepts, he/she gains at the other's expense
If both accept the deal they will both be punished to lesser extent
The dilemma: Each prisoner must choose between two choices without knowing what the other must do.
Action of A\Action of B Cooperate Defect
Cooperate Fairly good [+ 5] Bad [ - 10]
Defect Good [+ 10] Mediocre [0] Cooperation Group Selection
Some genes have an effect at the group level.
This effects whole-group fitness causing some groups to leave offspring while others do not. Key points:
If group selection occurs, it acts in addition to selection at the individual level.
Group selection tends to be most important when the population structure of a group involves interacting groups.
Group selection can act in the same direction as individual selection or in a different direction.
In order for a whole group to have a single trait (for group selection) it must first spread through the whole group by individual selection. Example:
Chickens Faking relatedness?
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