In simple reaching the hand is used to gather food with precision, and the type of grip and the posture are all evaluated. The tube task evaluates the hand used to extract food from the tube and the method of extraction (digital or instrumental). Through the handedness index we observed that the individuals show clear and strong individual lateralization for both tasks, particularly for the tube task (100%), but also for simple reaching (86%). Anyway, we did not detect population preferences for any of the tasks. However, considering both tasks jointly (multiple evaluation) it has been possible to detect for the first time a skilled manual dominance at the population level in semicaptive chimpanzees.
As a conclusion, our chimpanzee sample displays right handedness at population level when considering multitask values. This is the first time that data on handedness are recorded at population level in a chimpanzee sample living in an intermediate and naturalistic setting. Former researches on hand laterality with the same sample gave negative results (Mosquera et al. 2007), but that study was focused in unimanual and spontaneous tasks. Therefore, results of the current work point to three factors as decisive to force the displaying of hand laterality in chimpanzees: bimanual coordination, tool use, and grip precision.
Mosquera, M., Llorente, M., Riba, D., Estebaranz, F., González, M., Lorenzo, C., Sanmartí, N., Toll, M., Carbonell, E., & Feliu, O. (2007). Ethological study of manual laterality in naturalistic housed chimpanzees (Pan troglodytes) from the Mona Foundation Sanctuary (Girona, Spain). Laterality, 12, 19–30.
For more information:
Article "Manual Laterality for Simple Reaching and Bimanual Coordinated Task in Naturalistic Housed Pan troglodytes"
International Journal of Primatology, 30: 183-197.