Introduction The idea that mobility of upper limbs was least in prosimians, greater in monkeys, greater still in apes, and most in humans was a useful idea for viewing the primates in earlier times. But new information and ideas about primate locomotion now reveal that upper limb function is better described in other ways. The underlying difference between basically arboreal primates and terrestrial mammals: that is, in comparison to compressive forces in the forelimbs of terrestrial mammals, tension-bearing by upper limbs is a phenomenon of most activities that primates undertake. Thus, though tension-bearing is most easily seen in brachiation and arm-swinging, as practiced by some apes and monkeys, it is also a part of most locomotor actions that involve upper limb raising, body support from above, climbing, and other acrobatic movements, together with a wide variety of foraging and other activities only marginally within the concept of locomotion. Individual primates are less characterized by specific activities than they are by the amazing mix of activities, different in different primates, which they undertake. Thus, though all primates can do almost all things, the mix producing variable degrees of tension-bearing, is what distinguishes the various species from each other. It is perhaps also worth asking questions about locomotion in higher primates. Much attention has been paid to this in recent years so that leaping is well documented, for instance, as a major mode of locomotion. When we consider leaping in those other primates not usually thought of as leaping animals at all, we see mid-air positions in which limbs cycle or even wave wildly; it appears at first sight as though no good biomechanical mechanisms are at work at all. Thus, curious mid-air positions are found in forms such as macaques, mangabeys, gibbons, and spider monkeys. And the most unlikely mid-air positions of all are found in the most unlikely leapers of all, such species as spider monkeys, gibbons, and siamangs. Most naturalistic studies of primates did not begin until 1960; studies of the mode of locomotion began in 1967. Thus, information on the interrelationships of morphology, locomotion, and use of habitat is still incomplete. The Body of the paper The Grades of primate evolution Organismic studies suggest a linear arrangement of grades of primates from prosimians, through various monkeys, to apes and humans. The Lemuroids Primates have been traditionally considered to be closely related descendants of an early insectivore stock lumped Dermoptera (colugos, e.g., flying lemurs), Chiroptera (bats), Primates, and Menotyphla (e.g., tree shrews) into one monophyletic superordinal group, the Archon. He included tupaiids (tree shrews) with primates and other archons because he believed the skull structure of tupaiids was like lemuroids and different from insectivorous. Whether of limb girdles, limb segments, whole limbs, or overall bodily proportions) some representatives of genera from each morphological mode are analyzed, in no single study are all genera represented. For instance, for the shoulder girdle, information is presented for only one indriid form: the sifaka. For the pelvic