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Lecture 4

PSYCH 1XX3 Lecture Notes - Lecture 4: Organism, Inclusive Fitness, Eusociality


Department
Psychology
Course Code
PSYCH 1XX3
Professor
Joe Kim
Lecture
4

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Evolution 2
Intro
-Organism evolved to maximize fitness and reproduction, but why do we behave in ways
where we help others? ex: humans spend time helping others like family
How to make sense of this….
-Remember evolution acts at the level of genes and those genes that contribute to persons
fitness will get replicated more often, increasing in frequency throughout generations
-Referred to as “Selfish Gene”
-Implies that natural selection will favour the genes and gene complexes that best serve their
own interest, namely replication
BUT, why do we help others then? …..
Types of Social Behaviours
Effect on Actors Wellbeing
+
Actor—> One performing the act
ex: Behaviour HELPS actor but HURTS recipient = selfish
Cooperation= Personal Gain
-ex: Hockey, having one bad player so teaching them to be better (cost) to benefit in winning
-In evolution, increasing the fitness of others can sometimes improve your own fitness
prospects
Group Selection
-Adaptations aren't for the good of the group… They are for the good of the gene
-Increase in group success translates into better success for the metaphorical helping gene
-ex: Helping worst hockey player is good for whole team, but in evolutionary terms NOT good
enough reason
Good of the Group?…
-Geese foraging together, wouldn’t it make finding food more competitive?
-Not necessarily! When food is hard to find, it is better to have MORE geese to look around
and have opportunities to take food from others (cooperation)
-Another Advantage: When animals are busy looking for food, their attention is diverted and
predators are able to attack… “trade off”
-Thus there is a vilagent who looks for predators and the actual forager
-In bigger groups, the individual looks up less as a valiant and therefore is able to get more
food, and the whole group is more valiant all together… Spend less time scanning and more
time eating!
Effect on Recipient
wellbeing
+
Cooperation Altruism
Selfish Spite
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-Selection is not for the good of the group!
The Problems of Altruism
-Altruism: Behaviour in which the actor incurs a cost to provide a benefit to a recipient
-NOT Altruism: Foraging/vilagence in groups, because actor GAINS directly from behaviour
-ex: Lemmings… Suicide when population too large, altruistic gene dies off and selfish gene
lives on!
-Good of group cannot explain altruism or any other social behaviour
-
Eusocial Hymenoptera
-Includes all ants, some bees and wasps
-Most spend their lives serving the colony without reproducing
-How did altruism continue in evolution with animals such as bees serving the queen bee?..
Inclusive Fitness
-Evolutionary biologist W.D. Hamilton 1960’s
-Troubled by evolution of altruism and why natural selection favoured self sacrifice
-Realized that solution as simple as recognizing that genes for altruism could be successful if
they helped identical copies of themselves… Theory: Inclusive Fitness!
-Direct Fitness: Fitness from personal Reproduction
-Indirect Fitness: Fitness from the reproduction of close genetic relatives
-Direct Fitness+Indirect Fitness= Inclusive Fitness
-Means you can INCREASE your fitness by helping kin to successfully raise their offspring
-Because of Inclusive Fitness, natural selection can favour behaviours that increase
reproductive success AND behaviours that increase the reproductive success of close
genetic kin
-Shared genes between relatives can drive the evolution of altruism
Hamilton’s Rule
-Inequality that predicted when altruistic behaviours are favoured
-When br>c where “c” is reproductive cost to actor and “B” is reproductive benefit to the
recipient and “r” is the degree of relatedness between the two individuals
Inheritance and Hamilton's Rule
Relatedness
-Probability that actor and recipient share gene in question
-Depends on how genes were inherited
-ex: We get two copies of gene one form mom and dad. BUT copies are not identical! One
may be the same or different from the other one! And, ones they passed to siblings not
necessarily same as yours —> 50/50 from mom and 50/50 from dad.. we say theres a .5
relatedness to mom and .5 to dad of having inherited the gene from mom/dad
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