Altruism & Kin Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28, By: Elaine Rehm, Mika Galiher, Ebonie Buenrostro

Hypothesis 1.As the cost of helping another individual increases, the share of help given to kin will increase. Share given to non kin will decrease. 2.Association between help given and help received will be larger for acquaintances than for friends and larger for friends than siblings. Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28,

Hamilton’s Kin Selection Theory Greater relatedness is associated with higher levels of altruism. Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28,

Trivers Reciprocal Altruism Theory ● Altruism can enhance direct fitness as long as there is sufficient probability that it will be reciprocated. ● Reciprocation is less important among kin than non-kin, due to indirect benefits of helping kin. Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28,

Defining Altruism ● Altruism was defined through the breakdown of categories: low, medium and high cost help ● Low cost- emotional support ● Medium cost- help during an illness, during a crisis, everyday living, housing, financial support ● High cost- hypothetical scenario: ● Willingness to donate a kidney, ● Willingness to risk injury or death providing life saving help in an emergency (rescuing someone from a burning building) Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28,

Results Proved hypothesis one and two As the cost of help rose the relative ranking of friends fell Siblings received a larger share of medium cost help than low cost and larger high cost than medium cost help Acquaintances received a smaller share of medium than low cost help Friends received a smaller share of medium than low cost help Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28,

Conclusion ● Level of help was dependent on the cost of help, where as cost increased the share of help given to kin increased and non kin decreased. ● Participants were more likely to help in high cost situation for kin than non kin, possibly due to emotional ties. ● Acquaintances exhibited higher level of reciprocity than siblings or cousins compared to friends due to the wider temporal window in friendly relationships. ● Reciprocal exchange occurs more in acquaintances due to higher probability of reciprocity in a smaller temporal window. ● Consistent with RAT, where siblings and cousins engage in reciprocal altruism more than parents and offspring due to their close relation in age and experiences (we are more likely to help someone we feel closer to) Stewart-Williams, S. (2007) Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange. Evolution and Human Behavior, 28,

Critical Review Interesting findings: 1.Level of reciprocity for acquaintances was higher than for friends. 2.Generational pull of altruism, we are more likely to help those within our generation more so than parent and offspring due to close relation in age and experiences 3.The cost of the help was determining factor in all scenarios Weaknesses: 1.Scenario was based on hypothetical situation. 2.Not externally valid, lacking a representative sample of population- only sampled graduate students 3.Priming task may have had negative effects, could have done same without priming task.

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