title: The evolution of human and ape hand proportions.
abstract: Human hands are distinguished from apes by possessing longer thumbs relative to fingers. However, this simple ape-human dichotomy fails to provide an adequate framework for testing competing hypotheses of human evolution and for reconstructing the morphology of the last common ancestor (LCA) of humans and chimpanzees. We inspect human and ape hand-length proportions using phylogenetically informed morphometric analyses and test alternative models of evolution along the anthropoid tree of life, including fossils like the plesiomorphic ape Proconsul heseloni and the hominins Ardipithecus ramidus and Australopithecus sediba. Our results reveal high levels of hand disparity among modern hominoids, which are explained by different evolutionary processes: autapomorphic evolution in hylobatids (extreme digital and thumb elongation), convergent adaptation between chimpanzees and orangutans (digital elongation) and comparatively little change in gorillas and hominins. The human (and australopith) high thumb-to-digits ratio required little change since the LCA, and was acquired convergently with other highly dexterous anthropoids.
authors.affiliation: Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, Washington, DC 20052, USA.|Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York 11794, USA.|Institut Català de Paleontologia Miquel Crusafont (ICP), Universitat Autònoma de Barcelona, Edifici Z (ICTA-ICP), campus de la UAB, c/ de les Columnes, s/n., 08193 Cerdanyola del Vallès (Barcelona), Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Almécija
authors.affiliation: Department of Anthropology, Stony Brook University, Stony Brook, New York 11794, USA.
authors.forename: Jeroen B
authors.initials: JB
authors.lastname: Smaers
authors.affiliation: Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York 11794, USA.
authors.forename: William L
authors.initials: WL
authors.lastname: Jungers
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005385:Fingers / Q000033:anatomy & histology*; D005580:Fossils; D006071:Gorilla gorilla; D006225:Hand / Q000033:anatomy & histology; D015186:Hominidae; D006801:Humans; D009929:Organ Size; D002679:Pan troglodytes; D010802:Phylogeny; D057079:Pongo