Manual prehension, involved in food acquisition and locomotion, is common to all primates. However, the mechanisms of its emergence and evolution still remain to be elucidated. This prompts questions such as 1) what are the ecological factors (food and substrate properties) leading to an increase of the use of the hand in early primates, and 2) what functional factors (body posture, kinematics of the forelimb) are involved in the evolution of prehension in primates?The thesis project aims to determine the behavioural and kinematic strategies of unconstrained prehension in representative species of the major lineages of primates (the mouse lemur, lemur catta, capuchin, gorilla, chimpanzee, human).The behavioural strategies of the mouse lemur, convergent on early primates, suggest that arboreality and omnivory have played an important role in the origin of prehensile abilities in primates. The analysis of prehension in gorillas and humans shows a limited influence of body posture on the angular joint excursions and kinematic strategies. A comparison of all the species reveals that some kinematic invariants in the wrist velocity profile exist, independent of the species. Yet others appear to be related to the specific behaviour of the species. Moreover, two joint motion strategies divide the species, one favoring the rotations (gorillas and chimpanzees) and one involving more flexion-extension movements (lemurs, capuchins, humans). These joint motion strategies seem to have evolved independently of grasping ability.The results are discussed in the context of current work and theories on the origin and the evolution of prehension in primates.
