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Research shows that altruistic behaviours arise in varying social situations in line with different theories of causes of such behaviours. However most research uses financial costs only, which makes our understanding of altruism currently limited. This study presents findings of three experiments that use a novel and simple laboratory-based task that measures altruism based on the amount of time participants are willing to spend as a cost to help others. This task assessed two specific theories; altruistic punishment (Experiments 1 & 2) and empathy-altruism (Experiment 3). All experiments showed that the task was successful, as participants were more likely to altruistically punish violators of social contracts than other scenarios (Experiments 1 and 2), and also incur more costs to behave altruistically towards others when feeling empathic than different emotional states (Experiment 3). These results provide clear support for the use and value of this novel task in future research.

Altruism plays a role in mate choice, particularly in women’s preferences and in long-term (LT) relationships. The current study analyzed how these preferences interacted with another important mate choice variable, physical attractiveness. Here, female participants were presented with photographs of men of varying levels of physical attractiveness, alongside descriptions of them behaving either altruistically or not in different scenarios. The results showed women preferred altruistic men, particularly in LT relationships and that this interacted with physical attractiveness such that being both attractive and altruistic made a man more desirable than just the sum of the two desirable parts. Also, being altruistic made low attractive men more desirable but only for LT relationships. Finally, men who were just altruistic were rated more desirable than men who were just attractive, especially for LT relationships. Overall, these findings are discussed in terms of the role of altruism in mate choice, particularly in LT relationships and directions of future research.

In light of previous research showing that different types of relationships affect levels of testosterone in men, this study examined whether categorizing relationship types according to relationship length can shed further light on variations in levels of testosterone. Salivary testosterone samples were obtained from a sample of men and details about their relationship status, sociosexual orientation, extra-pair sexual interest, and their perceptions of their relationships were recorded. Using a median split analysis, participants who indicated that they had been in their relationship for less than 12 months were categorized as being in “new relationships” and those in longer relationships being categorized as in long-term relationships. Results showed that levels of testosterone of single men and men in new relationships did not differ, but both had significantly greater levels of testosterone than men in long-term relationships. Differences in levels of testosterone were unrelated to sociosexual orientation and extra-pair sexual interest. These findings support the evolutionary explanation of levels of testosterone in men varying in accordance with their internal motivation to seek new potential mates.

Face recognition has previously been used to provide evidence for the existence of human cheater detection mechanisms; however such evidence is currently inconclusive. This study aimed to further analyze recognition of violators and cooperators of rules by using two different contexts, social contracts (SC) and hazard management (HM). Participants were presented with male faces alongside either a SC or HM scenario and told whether the individual had violated or cooperated with the rule. Participants were then asked to identify the faces and behavior of those individuals from the first part of the study from a larger set of photographs. Results indicate that faces and behaviors of rule violators were remembered better than those of rule cooperators, and faces (but not behaviors) in SC scenarios were remembered better than those in HM scenarios. These results are interpreted as providing possible evidence of a general rule violator detection mechanism, with face recognition abilities then mediating differences between SC and HM scenarios. Furthermore, the disparity in how humans interpret SC and HM scenarios is discussed from an evolutionary perspective, with reference to how behavior in each rule affects the inclusive fitness of others.

Explaining human cooperation continues to present a challenge because it goes beyond what is predicted by established theories of kinship and reciprocal altruism. Little attention has been paid to the sexual selection hypothesis that proposes that cooperation can act as a display that attracts mates. The costs of cooperating are then offset not by kinship or reciprocation but by increased mating success. Here we present results from a series of experiments which show that, as predicted by the sexual selection hypothesis, people preferentially direct cooperative behavior towards more attractive members of the opposite sex. Furthermore, cooperative behavior increases the perceived attractiveness of the cooperator. Economically costly behaviors can therefore bring benefits through mate choice and sexual selection should be regarded as an evolutionary mechanism capable of promoting cooperation.