The evolution of self-control.

Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations.

Delay of gratification by orangutans (Pongo pygmaeus) in the accumulation task.

There is considerable evidence indicating that chimpanzees can delay gratification for extended time intervals, particularly in the accumulation task in which food items accumulate within a participant's reach until the participant begins to consume them. However, there is limited evidence that other ape species might also exhibit this capacity, despite there being a number of similar studies indicating that nonape species (e.g.

Gorillas' use of the escape response in object choice memory tests.

The ability to monitor and control one's own cognitive states, metacognition, is crucial for effective learning and problem solving. Although the literature on animal metacognition has grown considerably during last 15 years, there have been few studies examining whether great apes share such introspective abilities with humans. Here, we tested whether four gorillas could meet two criteria of animal metacognition, the increase in escape responses as a function of task difficulty and the chosen-forced performance advantage.

The effect of body orientation on judgments of human visual attention in western lowland gorillas (Gorilla gorilla gorilla).

The ability to appreciate the attentional states of others is an important element used in discerning the presence of Theory of Mind in an individual. Whether primates are able to recognize attention, and further, use such information to predict behavior, remains contentious. In this study, six western lowland gorillas (Gorilla gorilla gorilla) were tested under different conditions that aimed to investigate not only their understanding of what a human experimenter sees, but also what information they use to make these judgments.

Constructive and deconstructive tool modification by chimpanzees (Pan troglodytes).

Nine chimpanzees (Pan troglodytes) were tested for their ability to assemble or disassemble the appropriate tool to obtain a food reward from two different apparatus. In its deconstructed form, the tool functioned as a probe for one apparatus. In its constructed form, the tool functioned as a hook, appropriate for a second apparatus.