Evolutionary Theory Part 2Evolutionary Theory Part 2

Goals for today...Goals for today...

• Kin selection and reciprocal altruismKin selection and reciprocal altruism

• How do you assess adaptive value of a How do you assess adaptive value of a behavior?behavior?

• Look at some behavioral examplesLook at some behavioral examples

• Introduce some models to explain Introduce some models to explain primate behaviorprimate behavior

Kin selectionKin selection

• A form of Natural selectionA form of Natural selection

• Individual’s fitness is influenced by Individual’s fitness is influenced by fitness of relatives (they share genes!)fitness of relatives (they share genes!)

Graph Strier pg 123

Behavioral choices...Behavioral choices...

• Altruism-Altruism- an act that benefits the helper at some cost but helps the receiver.

• Selfish-Selfish-acting on acting on your own self interest your own self interest to improve your to improve your fitness at cost to fitness at cost to other’s fitness other’s fitness

How do you predict altruism?How do you predict altruism?

Hamilton’s Rule

c

Act’s benefit to receiver’s fitness

Degree of relatedness between actor and

receiver

Act’s cost to actor’s fitness

b r< x

• Brother’s helping Brother’s helping rear offspring. rear offspring.

• R = .5R = .5• Benefits to helper’s Benefits to helper’s

fitness should be at fitness should be at least twice the cost. least twice the cost.

• Half brothers helping Half brothers helping rear offspringrear offspring

• R = .25R = .25• Benefits to helper’s Benefits to helper’s

fitness should be at fitness should be at least four times the least four times the cost. cost.

Reciprocal AltruismReciprocal Altruism

• Behavior which is costly to actor but Behavior which is costly to actor but immediately benefits receiver (who is not immediately benefits receiver (who is not related)- at some later time, receiver related)- at some later time, receiver reciprocates. reciprocates.

– Low dispersal ratesLow dispersal rates

– Social groupsSocial groups

– Ability to discriminate between individualsAbility to discriminate between individuals

– Time frameTime frame

CoalitionsCoalitions

Hamadryas baboon Rhesus monkey

Chimpanzee politicsChimpanzee politicsYereon- dom. male

Luit challenges,No female support

Luit and Nikkie formCoalition, Nikkie gainsFemale support

Luit, Nikkie then overthrow Yereon

Luit- dom. MaleNikkieYereon

Yereon and Nikkieoverthrow Luit

Nikkie- dom. male

Criterion used to evaluate adaptation?Criterion used to evaluate adaptation?

• Evaluate Evaluate costscosts and and benefitsbenefits

• The compromise between these is theThe compromise between these is the optimal strategyoptimal strategy

• How easily is this done in primatology?How easily is this done in primatology?

Behavioral Examples...Behavioral Examples...

• InfanticideInfanticide

InfanticideInfanticide

• Male tenure important factorMale tenure important factor

• Female strategiesFemale strategies

• Female counterstrategiesFemale counterstrategies

Monogamy (pairbonding)Monogamy (pairbonding)

Males Costs

•Mate with one female•Expend energy defending territory

Males benefits

•Paternal certainty• Exclusive access to resources

Monogamy (pairbonding)Monogamy (pairbonding)

Female Costs

•Limited mate choice•Expend energy defending territory

Females benefits

• Male care• Exclusive access to resources