Is the sense of fairness uniquely human? Human reactions to reward division are often studied by means of the ultimatum game, in which both partners need to agree on a distribution for both to receive rewards. Humans typically offer generous portions of the reward to their partner, a tendency our close primate relatives have thus far failed to show in experiments. Here we tested chimpanzees (Pan troglodytes) and human children on a modified ultimatum game. One individual chose between two tokens that, with their partner's cooperation, could be exchanged for rewards. One token offered equal rewards to both players, whereas the other token favored the chooser. Both apes and children responded like humans typically do. If their partner's cooperation was required, they split the rewards equally. However, with passive partners-a situation akin to the so-called dictator game-they preferred the selfish option. Thus, humans and chimpanzees show similar preferences regarding reward division, suggesting a long evolutionary history to the human sense of fairness.inequity aversion | equality | reciprocity | sharing | behavioral economics

Children are selective and flexible imitators. They combine their own prior experiences and the perceived causal efficacy of the model to determine whether and what to imitate. In Experiment 1, children were randomly assigned to have either a difficult or an easy experience achieving a goal. They then saw an adult use novel means to achieve the goal. Children with a difficult prior experience were more likely to imitate the adult's precise means. Experiment 2 showed further selectivitychildren preferentially imitated causally efficacious versus nonefficacious acts. In Experiment 3, even after an easy prior experience led children to think their own means would be effective, they still encoded the novel means performed by the model. When a subsequent manipulation rendered the children's means ineffective, children recalled and imitated the model's means. The research shows that children integrate information from their own prior interventions and their observations of others to guide their imitation.

The authors argue that imitation is a flexible and adaptive learning mechanism in that children do not always reproduce all of the details they can from a demonstration. Instead, they vary their replications depending on their interpretation of the situation. Specifically, the authors propose that when children do not understand the overall reason for a model's behavior, they will be more likely to imitate precisely. By copying conservatively in these situations, children may have a good chance of reproducing the action of the model correctly. In contrast, when the reason for an action is clear, children will be more likely to deviate from the manners and flourishes of the model and use their own means to complete the action.

Children understand gesture+speech combinations in which a deictic gesture adds new information to the accompanying speech by age 1;6 (Morford & Goldin-Meadow, 1992; ‘push’+point at ball). This study explores how early children understand gesture+speech combinations in which an iconic gesture conveys additional information not found in the accompanying speech (e.g., ‘read’+BOOK gesture). Our analysis of two- to four-year-old children's responses in a gesture+speech comprehension task showed that children grasp the meaning of iconic co-speech gestures by age three and continue to improve their understanding with age. Overall, our study highlights the important role gesture plays in language comprehension as children learn to unpack increasingly complex communications addressed to them at the early ages.

Two experiments were used to investigate the scope of imitation by testing whether 36-month-olds can learn to produce a categorization strategy through observation. After witnessing an adult sort a set of objects by a visible property (their color; Experiment 1) or a nonvisible property (the particular sounds produced when the objects were shaken; Experiment 2), children showed significantly more sorting by those dimensions relative to children in control groups, including a control in which children saw the sorted endstate but not the intentional sorting demonstration. The results show that 36-month-olds can do more than imitate the literal behaviors they see; they also abstract and imitate rules that they see another person use.