Thoracic adaptations for ventilation during locomotion in humans and other mammals

Abstract

Bipedal humans, like canids and some other cursorial mammals, are thought to have been selected for endurance running, which requires the ability to sustain aerobic metabolism over long distances by inspiring large volumes of air for prolonged periods of time. Here we test the general hypothesis that humans and other mammals selected for vigorous endurance activities evolved derived thoracic features to increase ventilatory capacity. To do so, we investigate whether humans and dogs rely on thoracic motion to increase tidal volume during running to a greater extent than goats, a species that was not selected for endurance locomotion. We found that while all three species use diaphragmatic breathing to increase tidal volume with increasing oxygen demand, humans also use both dorsoventral and mediolateral expansions of the thorax. Dogs use increased dorsoventral expansion of the thorax, representing an intermediate between humans and goats. 3D analyses of joint morphology of 10 species across four mammalian orders also show that endurance-adapted cursorial species independently evolved more concavo-convex costovertebral joint morphologies that allow for increased rib mobility for thoracic expansion. Evidence for similarly derived concavo-convex costovertebral joints in Homo erectus corresponds with other evidence for the evolution of endurance running in the genus Homo.