Evolutionary Theory Part 2

Goals for today... Kin selection and reciprocal altruismKin selection and reciprocal altruism How do you assess adaptive value of a behavior?How do you assess adaptive value of a behavior? Look at some behavioral examplesLook at some behavioral examples Introduce some models to explain primate behaviorIntroduce some models to explain primate behavior

Kin selection A form of Natural selectionA form of Natural selection Individual’s fitness is influenced by fitness of relatives (they share genes!)Individual’s fitness is influenced by fitness of relatives (they share genes!) Graph Strier pg 123

Behavioral choices... Altruism-Altruism- an act that benefits the helper at some cost but helps the receiver. Selfish-acting on your own self interest to improve your fitness at cost to other’s fitness

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 br<x

Brother’s helping rear offspring.Brother’s helping rear offspring. R =.5R =.5 Benefits to helper’s fitness should be at least twice the cost.Benefits to helper’s fitness should be at least twice the cost. Half brothers helping rear offspring R =.25 Benefits to helper’s fitness should be at least four times the cost.

Reciprocal Altruism Behavior which is costly to actor but immediately benefits receiver (who is not related)- at some later time, receiver reciprocates.Behavior which is costly to actor but immediately benefits receiver (who is not related)- at some later time, receiver reciprocates. –Low dispersal rates –Social groups –Ability to discriminate between individuals –Time frame

Coalitions Hamadryas baboon Rhesus monkey

Chimpanzee politics Yereon- dom. male Luit challenges, No female support Luit and Nikkie form Coalition, Nikkie gains Female support Luit, Nikkie then overthrow Yereon Luit- dom. Male Nikkie Yereon Yereon and Nikkie overthrow Luit Nikkie- dom. male

Criterion used to evaluate adaptation? Evaluate costs and benefitsEvaluate costs and benefits The compromise between these is the optimal strategyThe compromise between these is the optimal strategy How easily is this done in primatology?How easily is this done in primatology?

Behavioral Examples... InfanticideInfanticide

Infanticide Male tenure important factorMale tenure important factor Female strategiesFemale strategies Female counterstrategiesFemale counterstrategies

Monogamy (pairbonding) Males Costs Mate with one female Expend energy defending territory Males benefits Paternal certainty Exclusive access to resources

Monogamy (pairbonding) Female Costs Limited mate choice Expend energy defending territory Females benefits Male care Exclusive access to resources