Dopamine receptor D4 gene variation predicts preschoolers' developing theory of mind.

Individual differences in preschoolers' understanding that human action is caused by internal mental states, or representational theory of mind (RTM), are heritable, as are developmental disorders such as autism in which RTM is particularly impaired. We investigated whether polymorphisms of genes affecting dopamine (DA) utilization and metabolism constitute part of the molecular basis of this heritability. Seventy-three 42- to 54-month-olds were given a battery of RTM tasks along with other task batteries that measured executive functioning and representational understanding more generally. Polymorphisms of the dopamine D4 receptor gene (DRD4) were associated with RTM performance such that preschoolers with shorter alleles outperformed those with one or more longer alleles. However, polymorphisms of the catechol-O-methyl transferase gene (COMT) and the dopamine transporter gene (DAT1) genes were not associated with children's RTM performance. Further tests showed that the association between DRD4 allele length and RTM performance was not attributable to a common association with executive functioning or representational understanding more generally. We conclude that DRD4 receptors, likely via their effects on frontal lobe development and functioning, may represent a neuromaturational constraint governing the stereotypical and universal trajectory of RTM development.

Do as I do: 7-month-old infants selectively reproduce others' goals.

In the current study, we tested whether 7-month-old infants would selectively imitate the goal-relevant aspects of an observed action. Infants saw an experimenter perform an action on one of two small toys and then were given the opportunity to act on the toys. Infants viewed actions that were either goal-directed or goal-ambiguous, and that represented either completed or uncompleted goals. Infants reproduced the goal of the experimenter only in those cases where the action was goal-directed, in both the complete and incomplete goal conditions. These results provide the first evidence that infants as young as 7 months of age selectively imitate actions based on their goal-directedness, and that they are able to analyze the goals of even uncompleted actions. Even during the first year of life, infants' sensitivity to goal-directed action is expressed not only in their responses in visual habituation procedures, but also in their overt actions.

The ecology and evolution of patience in two New World monkeys.

Decision making often involves choosing between small, short-term rewards and large, long-term rewards. All animals, humans included, discount future rewards--the present value of delayed rewards is viewed as less than the value of immediate rewards. Despite its ubiquity, there exists considerable but unexplained variation between species in their capacity to wait for rewards--that is, to exert patience or self-control. Using two closely related primates--common marmosets (Callithrix jacchus) and cotton-top tamarins (Saguinus oedipus)--we uncover a variable that may explain differences in how species discount future rewards. Both species faced a self-control paradigm in which individuals chose between taking an immediate small reward and waiting a variable amount of time for a large reward. Under these conditions, marmosets waited significantly longer for food than tamarins. This difference cannot be explained by life history, social behaviour or brain size. It can, however, be explained by feeding ecology: marmosets rely on gum, a food product acquired by waiting for exudate to flow from trees, whereas tamarins feed on insects, a food product requiring impulsive action. Foraging ecology, therefore, may provide a selective pressure for the evolution of self-control.