Altruism towards non-relatives is often explained within the framework of Robert Trivers' reciprocal altruism. What this paper demonstrates is that people (and especially women) find altruists more attractive. Thus, altruism can be seen as a sexually selected trait, and advertisement of one's propensity to be giving, and hence, presumably be a good parent and provider.
British Journal of Psychology doi: 10.1348/000712608X298467
Do humans prefer altruistic mates? Testing a link between sexual selection and altruism towards non-relatives
Tim Phillips et al.
Humans are often seen as unusual in displaying altruistic behaviour towards non-relatives. Here we outline and test a hypothesis that human altruistic traits evolved as a result of sexual selection. We develop a psychometric scale to measure mate preference towards altruistic traits (the MPAT scale). We then seek evidence of whether mate choice on the basis of altruistic traits is present and find it in one study (N=170 couples). We also predict that a stronger female MPAT, as measured by responses to the MPAT scale, will be expressed - a result found in all three studies (Ns=380, 340, and 398). Both sets of results are consistent with the hypothesized link between human altruism towards non-relatives and sexual selection.