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Lecture 19

BIOL 3062 Lecture 19: reciprocity

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Dalhousie University
BIOL 3062
Andy Horn

Lecture 19: Reciprocity Mutualism - Get biggest immediate gain/payoff by cooperating o Biggest payoff from cooperating - Donor deciding whether to cooperate o Compatriot also will help if you do Snow drift - Need to dig out cars to get to university o Can help house mate to dig out car or just sleep in, or just sleep in and not deal with costs of helping ▪ If you both dig it out, you split the cost ▪ Biggest cost if you try to dig out car on own ▪ Most tempting to defect • Defecting (stay in bed) has the highest benefit ▪ no one goes out to shuffle and no one gets the benefit of getting the cars out • Intuition says to go out and both get the car out so as a whole, both individuals are better off o Even though would be better off free-loading from an individual point of view Prisoner’s dilemma - When donor cooperates, suffer the costs if recipient freeloads o Temptation is huge to defect ▪ Defection is always on top • Technically, if all agreed, everyone would receiver benefit, but the temptation to defect is too high to cooperate o So how do we get ESS for cooperation? Altruism - Increasing another individual’s fitness (b) at a cost (c) to one’s own direct fitness o Altruism works is probability of running into/associating with another altruist is greater than the probability of an altruist running into a non-altruist ▪ Altruists being related increasing this likelihood • Relatedness increasing the predictability of the recipient also being related ▪ Altruists also commonly interact repeatedly • See reciprocity in behaviour o Less likely to show altruistic behaviour towards those who do not reciprocate ▪ When there is no back-and-forth, altruist stops
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