Mechanical constraints appear to require that locomotion and breathing be synchronized in running mammals. Phase locking of limb and respiratory frequency has now been recorded during treadmill running in jackrabbits and during locomotion on solid ground in dogs, horses, and humans. Quadrupedal species normally synchronize the locomotor and respiratory cycles at a constant ratio of 1:1 (strides per breath) in both the trot and gallop. Human runners differ from quadrupeds in that while running they employ several phase-locked patterns (4:1, 3:1, 2:1, 1:1, 5:2, and 3:2), although a 2:1 coupling ratio appears to be favored. Even though the evolution of bipedal gait has reduced the mechanical constraints on respiration in man, thereby permitting greater flexibility in breathing pattern, it has seemingly not eliminated the need for the synchronization of respiration and body motion during sustained running. Flying birds have independently achieved phase-locked locomotor and respiratory cycles. This hints that strict locomotor-respiratory coupling may be a vital factor in the sustained aerobic exercise of endothermic vertebrates, especially those in which the stresses of locomotion tend to deform the thoracic complex.

No abstract

HOMINIDS from other primates is not large brain size, but the set of characters associated with erect bipedal posture and a striding gait. Long before the rapid increase in relative brain size that took place during the Pleistocene, early australopithecines possessed the postcranial morphology of an erect, striding biped (Lovejoy, Heiple, and Burstein 1973). Evidence for the bipedal gait of early hominids is provided by the morphology of the 3.5-millionyear-old postcranial material from the Hadar Formation of Ethiopia (Johanson, Taieb, and Coppens 1982, Lovejoy, Johanson, and Coppens 1982), early Pleistocene material from eastern and southern Africa (Preuschoft 1971), and the Pliocene trackways (3.6 to 3.8 million years old) discovered at Laetoli in northern Tanzania (Leakey and Hay 1979, White 1980). Together these suggest that early australopithecines were relatively small-brained creatures, possessing structural adaptations for upright walking and running that in a broad sense are remarkably similar to those of modern man. The aspects of locomotion that unite the hominids as a group are also uniquely hominid in character and distinctly peculiar for mammals. Consequently, the study of human locomotion, in addition to explaining much of the biology of the one remaining hominid, may prove to be one of the more powerful inductive approaches to the study of hominid evolution. The energetic cost of transport (oxygen consumption per unit body mass per unit distance traveled) for running humans is relatively high in comparison with that for other mammals and running birds. Early comparative studies showed that a mam-1 This contribution arose out of conversations with D. M. Bramble and S. C. Carrier. Further development resulted from discussions with C. Gans and M. H. Wolpoff. For critical review and additional improvement of this manuscript, I am grateful to S.

Although the bones of rapidly growing animals are composed of weak tissue, they often must function in locomotor activity. We address the conflict between development and skeletal function by analysing the ontogeny of skeletal strength in the California gull, Larus californicus. Changes in shape and mechanical properties of the femur, tibia, tarsometatarsus, humerus, ulna and carpometacarpus were analysed in a complete post‐hatching growth series. During post‐hatching growth, strength and stiffness of the skeletal tissue increases six‐ to ten‐fold. At hatching, long bones of the wing are relatively weak and they remain so throughout the major portion of the growth period. However, in the hind limb, relatively thick bones in juveniles compensate for the weak tissue such that the force required to break the bones remains constant relative to body mass. This difference between hind limb and wing parallels the development of locomotor function; young gulls begin to walk within a day or two of hatching, but they do not fly until they are fully grown. Thus, in the bones of the hind limb, the conflict between rapid growth and skeletal function is solved by negative allometry of bone thickness. After young gulls reach adult size, the breaking strength of the wing bones increases three‐ to four‐fold, the mass of the pectoralis muscle triples and the surface area of the wing doubles. The one aspect of wing development that is not delayed until shortly before fledging is linear growth of the bones. Bones of the wing increase in length at a rapid and relatively constant rate from the time of hatching to the attainment of adult size. Relatively early initiation of linear growth of the wing bones suggests that the rate at which bones grow in length may be the rate limiting factor in wing development.