Inclusive fitness theory provides a compelling explanation for the evolution of altruism among kin. However, a completely satisfactory account of non-kin altruism is still lacking. The present study compared the level of altruism found among siblings with that found among friends and mates and sought to reconcile the findings with an evolutionary explanation for human altruism. Participants (163 males and 156 females) completed a questionnaire about help given to a sibling, friend, or mate. Overall, participants gave friends and mates as (...) much or more help than they gave siblings. However, as the cost of help increased, siblings received a progressively larger share of the help, whereas friends and mates received a progressively smaller share, despite the fact that participants were closer emotionally to friends and mates than they were to siblings. These findings help to explain the relative standing of friends and mates as recipients of altruistic aid. (shrink)

Insults elicit intense emotion. This study tests the hypothesis that one's social image, which is especially salient in honour cultures, influences the way in which one reacts to an insult. Seventy-seven honour-oriented and 72 non-honour oriented participants answered questions about a recent insult episode. Participants experienced both anger and shame in reaction to the insult. However, these emotions resulted in different behaviours. Anger led to verbal attack (i.e., criticising, insulting in return) among all participants. This relationship was explained by participants’ (...) motivation to punish the wrongdoer. Shame, on the other hand, was moderated by honour. Shame led to verbal disapproval of the wrongdoers behaviour, but only among the honour-oriented participants. This relationship was explained by these participants’ motivation to protect their social image. By contrast, shame led to withdrawal among non-honour-oriented participants. (shrink)

Supporting Hamilton’s inclusive fitness theory, archival analyses of inheritance patterns in wills have revealed that people invest more of their estates in kin of closer genetic relatedness. Recent classroom experiments have shown that this genetic relatedness effect is stronger for relatives of direct lineage (children, grandchildren) than for relatives of collateral lineage (siblings, nieces, nephews). In the present research, multilevel modeling of more than 1,000 British Columbian wills revealed a positive effect of genetic relatedness on proportions of estates allocated to (...) relatives. This effect was qualified by an interaction with lineage, such that it was stronger for direct than for collateral relatives. Exploratory analyses of the moderating role of benefactors’ sex and estate values showed the genetic relatedness effect was stronger among female and wealthier benefactors. The importance of these moderators to understanding kin investment in modern humans is discussed. (shrink)