Featured Articles in This Month's Animal Behaviour

The concept of what is fair seems to be deeply imbedded in the human psyche. Equal pay for equal work has been a rallying call for some since the industrial revolution. To see others get a better reward for the same job is aggravating as is ‘bait and switch’ when a better prize is first offered and a lesser one given. The question is, how far back in evolutionary history do these sentiments go? To examine this question, experiments have been set up with primates and quite a few other nonhuman species whereby one individual sees another get a better reward for completing the same task. Sometimes this lesser reward is rejected but responses to this inequity are variable within and across species. Responses can be influenced by rank, sex, age and social group. In this issue (pp. 75e87) Sarah Brosnan of Georgia State University and her associates asked whether personality attributes also explain some of the differences in the behavioural response to inequity. They also asked whether personality traits affected responses similarly when individuals had been shown a better reward than what they ultimately received. Twenty-four chimpanzees from four social groups were allowed to choose to participate with a particular partner. Pairs alternated trading a token to receive a food reward (Fig. 1) that was the same or of less value than what they saw their partner receive (inequity condition) or the reward was of less value than what they had been previously shown (contrast condition in which the outcome is compared to a nonsocial referent such as past experience). In the control condition, both subjects were offered and received the same, less preferred reward. Brosnan et al. predicted that both personality and the quality and duration of the pair's relationship would influence the chimpanzees' reaction to these ‘unfair’ conditions. After establishing that all chimpanzees preferred a grape to a piece of raw carrot and after they had been trained to exchange a length of PVC pipe for the reward, each pair was tested in the inequity, contrast and equity control conditions with partners alternating as subject. Personality ratings were collected from questionnaires from staff members. The 41 traits were reduced to six dimensions: methodical, extraversion, agreeableness, openness, reactivity/undependability and dominance. Information on the quality of the relationship was collected through scan samples of interactions scoring contact, proximity and grooming. The length of time that the subjects had lived in the same social group was also considered. Subjects refused to accept the less desirable reward between about 20 and 40% of the time, which varied significantly depending