In general, the adult subjects used in-hand movements more frequently and used a wider variety of forms than did the young juvenile subjects, suggesting that in-hand movements are in the process of fine-tuning around the age of 5 years in chimpanzees. We describe in detail the in-hand movements they used and the variability observed in form and execution among the subjects. While attempting to insert the objects through the cutouts, the subjects used at least two forms of in-hand movements to change their grip on the object for more precise alignment. We presented adult and young juvenile chimpanzees (ages 5–29 years) with a task that required inserting small objects through correspondingly shaped cutouts in a transparent Plexiglas panel. In-hand movements are defined as the movement of an object within one hand via manipulation of the digits. Here, we describe several forms of in-hand movements used by chimpanzees (Pan troglodytes) when manipulating small objects. The set of characteristics was compared with data from analyses of fossilised bones of early hominids.ĭescriptions of manual function in nonhuman primates have largely focused on static precision and power grasping (as first defined by Napier,1956), while identification and description of dynamic manual function are rare and incomplete. Based on biomechanical and technological studies we arrived at a number of characteristics in the morphological structure of upper limbs which could make it easier to specify which species had been capable of making tools. This was compared with technological analyses of Lower Paleolithic materials. Detailing the biomechanics of lithic reduction (stone knapping) by Homo sapiens enabled us to establish the required sequence of movements. Analyses of the upper extremities of hominini are based on the comparison with well-studied principles which govern the functioning of the upper limb of Homo sapiens. A juxtaposition of morphological characteristics of fossilised bones with precise technological analyses, in particular studies on operational sequences (chaîne opératoire) and debitage reassembly, allows us to determine which movement sequences were necessary to make tools. ![]() This article discusses the subject of manipulative skills of early hominids in the context of stone toolmaking capabilities.
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