Body composition in Pan paniscus compared with Homo sapiens has implications for changes during human evolution

During human evolution, the body changed in shape, partially to accommodate bipedal locomotion. Concurrently, brain size underwent a three-fold increase recorded in evidence from fossils and from comparative anatomy of chimpanzees, Homo sapiens’ closest living relatives. Because soft tissues like muscle, skin, and fat do not fossilize, and little information is available on these components for the genus Pan, reconstructing tissue changes has primarily relied on what is known about humans. This study presents unique quantitative data on major body components of muscle, bone, skin, and fat of 13 bonobos (Pan paniscus) for interpreting evolutionary forces that have shaped the human form for survival in a savanna mosaic environment., The human body has been shaped by natural selection during the past 4–5 million years. Fossils preserve bones and teeth but lack muscle, skin, fat, and organs. To understand the evolution of the human form, information about both soft and hard tissues of our ancestors is needed. Our closest living relatives of the genus Pan provide the best comparative model to those ancestors. Here, we present data on the body composition of 13 bonobos (Pan paniscus) measured during anatomical dissections and compare the data with Homo sapiens. These comparative data suggest that both females and males (i) increased body fat, (ii) decreased relative muscle mass, (iii) redistributed muscle mass to lower limbs, and (iv) decreased relative mass of skin during human evolution. Comparison of soft tissues between Pan and Homo provides new insights into the function and evolution of body composition.