Primate evolution. Historical artwork of various primate skeletons, showing their evolutionary similarities and differences. The skeletons are (left to right): a gibbon (family Hylobatidae), an orangutan (Pongo pygmaeus), a chimpanzee (Pan troglodytes), a gorilla (Gorilla gorilla) and a human (Homo sapiens). All primates display certain physical characteristics such as opposable thumbs, big toes and forward-directed eyes with binocular vision. Man has a larger skull capacity than other primates as well as shorter arms and smaller feet and hands. The other primates (except the gibbon) are essentially four-footed. The gorilla is by far the most physically powerful primate, with a bigger frame and larger pelvis. Artwork from The Outline of Science (J. Arthur Thomson, 1922).