International Journal of Comparative Psychology

Two orangutans’ and one gorilla’s understanding of social relationships was investigated using twodimensional photographs displayed on a touch-screen monitor. Unlike the photos used in similar studies, the photos presented here were not of exclusively familiar or related individuals, thus eliminating the use of previously learned associations or “genetic” similarities as cues. In Experiment 1, the subjects discriminated photos of mother-offspring pairs from photographs depicting other social relationships (siblings, unrelated group mates, mated pairs). In Experiment 2, they matched photos of mother-offspring pairs, mated pairs, siblings and groups of animals in a delayed matchingto- sample task (DMTS). In Experiment 3, they matched photographs depicting various behaviors (sleeping, eating, playing and grooming) in another DMTS procedure. Performance was significantly above chance in all three experiments, suggesting that both species of Great Ape might be sensitive to abstract concepts such as social relationships and activities.