Evolutionary principles suggest that there will be differences in the nature of altruism directed toward kin vs. nonkin. The present study sought to explore these differences. Participants were 295 undergraduate students who each completed a questionnaire about help exchanged with siblings, cousins, acquaintances or friends. For siblings, cousins and acquaintances, greater relatedness was associated with higher levels of helping. Friends were an exception, however, receiving as much or more help than kin. Consistent with an evolutionary analysis, as the cost of helping increased, kin received a larger share of the help given, whereas nonkin received a smaller share. For low-cost help, people helped friends more than siblings; for medium-cost help, they helped siblings and friends equally; and for high-cost help, they expressed a greater willingness to help siblings than friends. As expected, the level of reciprocal exchange was higher among acquaintances than among friends; however, there was also an unexpectedly high level of reciprocal exchange among kin.
In many species, greater relatedness is associated with higher levels of altruism, a pattern that makes good sense in light of Hamilton's (1964) kin selection theory (KST). Data from various sources indicate that humans are no exception (Burnstein et al., 1994, Daly & Wilson, 1988, Essock-Vitale & McGuire, 1985, Korchmaros & Kenny, 2001, Korchmaros & Kenny, 2006, Neyer & Lang, 2003, Tooley et al., 2006 and Webster, 2003). Considered in isolation, however, KST is unable to explain much of the data on human altruism. First, although unrelated acquaintances receive less help than kin (Burnstein et al., 1994), they do typically receive some help. In addition, certain categories of nonkin are exceptions to the general rule that people help kin more than nonkin. This includes friends, who often receive as much or more help than kin (Cialdini et al., 1997, Essock-Vitale & McGuire, 1985 and Kruger, 2003). The present study explored some of the ways in which these findings can be reconciled with KST.
1.1. Cost of helping
An initial suggestion concerns the cost of help. Although KST does not rule out the evolution of nonkin altruism, it does imply that it cannot be selected unless there is a return benefit to the altruist or the altruist's kin (but see Fehr & Henrich, 2003, Gintis, 2000 and Richerson et al., 2003, for discussion of how genetic or cultural group selection could produce altruism in the absence of any such benefit). There are various channels through which return benefits could come, e.g., through the reciprocation of help, an increase in mating opportunities, or an enhancement of the altruist's reputation (Gurven, 2004). However, it is never guaranteed that altruism will bring a return benefit, and the greater the cost of altruism, the greater the net direct fitness cost if it does not. This is less problematic when the recipient is a genetic relative, because the direct fitness cost may be compensated by the indirect fitness benefit associated with aiding relatives. So, although people may be altruistic toward nonkin, one would expect that this would be somewhat dependent on the cost of help. This leads to the following hypothesis:
Hypothesis 1.
As the cost of helping increases, the share of help given to kin will increase, and the share given to nonkin will decrease.
1.2. Levels of reciprocal exchange
A second suggestion involves considering KST in tandem with Trivers's (1971) reciprocal altruism theory (RAT), according to which altruism can enhance direct fitness as long as there is sufficient probability that it will be reciprocated. Again, reciprocation is less important among kin than among nonkin, because the indirect fitness benefits of helping kin can outweigh the direct fitness costs of unreciprocated help. This has led to the suggestion that kin will exhibit a lower level of reciprocity than nonkin, a hypothesis that has found some support (Berté, 1988, Essock-Vitale et al., 1980, Essock-Vitale & McGuire, 1985, Hames, 1987 and Gurven et al., 2001). There is a complication, however. Some commentators argue that RAT does not provide an adequate explanation for altruism among close friends (Roberts, 2005, Silk, 2003 and Tooby & Cosmides, 1996). People are often angered by the suggestion that their friendships are founded on the exchange of favors, and deny that when they help their friends they do so with the expectation of immediate repayment. This rules out strict tit-for-tat reciprocity as a model for altruism among friends. However, equity and reciprocity are nonetheless important in friendships (Silk, 2003). It remains possible, therefore, that friendships are founded on reciprocity but that exchanges of help among friends take place within an extended timeframe, with friends tolerating longer periods of imbalance. This leads to the hypothesis that there will be a higher level of reciprocity among acquaintances than among friends. However, because kinship reduces the need for reciprocation, the level of reciprocity found among kin will be lower still than that among friends.
Hypothesis 2.
The association between help given and help received will be larger for acquaintances than for friends, and larger for friends than for siblings or cousins.
