Donating Blood as a Costly Signal 

Lam, M. (University of Queensland), Masser, B.M. (University of Queensland), Dixson, B.J. (University of Queensland) 

Costly signals are behaviours that are linked to underlying traits and are beneficial to signal, but are costly for the individual to perform. Researchers have proposed that donating blood is a costly signal, but it is unclear which traits and benefits are associated with this behaviour. We examined this in three studies. In Study 1 (N = 227), blood donors and non-donors completed a range of measures of altruism. In Study 2 (N = 210), participants played a trust game with different targets (e.g., blood donor, student). Study 3 (N = 359) manipulated how frequently the altruistic behaviour was performed to examine whether this influenced perceptions of the altruist. Blood donors and non-blood donors responded similarly to the measures of altruism. However, targets described as altruistic were allocated significantly more money in the trust game compared to neutral targets. Further, the frequency of altruism influenced perceptions. At high frequency, blood donors were perceived as significantly more altruistic, but less healthy than a neutral target. At low frequency, there were no significant differences in perceptions of altruism, but blood donors were rated to be significantly healthier than all other targets. These findings suggest that health, rather than altruism, may be the key trait signalled by blood donation. 

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Emotion, Norms, and Pro-social behaviour