In contrast, the study of bonobos' manipulative abilities has almost exclusively been carried out in experimental contexts related to tool use. In particular, the manipulative abilities of our closest relatives, the chimpanzee (Pan troglodytes), have been widely described in various contexts, showing a high level of dexterity both in zoo and in natural conditions. The results are discussed in relation to the idea that visual information related to orientating food items of varying sizes to an appropriate position in the mouth contributed to the evolution of the visual control of hand shaping skills in anthropoid primates.Ĭomparative behavioral studies of hand use amongst primate species, including humans, have been central in research on evolutionary mechanisms. Large food items that protruded from the hand were visually monitored to orient the food item on the initial part of the withdraw but visually disengaged with a head movement and often a blink before the item was placed in the mouth. Small food items were brought directly to the mouth with hand supination, often with no visual monitoring after grasping.
The present study finds that Balinese long-tailed macaques (Macaca fascicularis), video recorded while spontaneously eating at the Sacred Monkey Forest Sanctuary in Ubud in Indonesia, displayed two types of hand movements associated with two types of withdraw movements to place food items in the mouth. The subsequent evolution of the visual control of hand and finger shaping movements of the grasp of anthropoids is uncertain. Contemporary theory holds that a small-bodied stem primate evolved visual control of the reach to guide a hand to obtain small insects and fruit items from the terminal branches of trees. The details of the evolutionary steps in the transition from nonvisual guidance of hand movements for feeding, as displayed by many non-primate species, to visual guidance of hand movements in primates are sparse.
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