![]() This shift resurrected the ‘troglodytian’ stage in human evolution, which assumes that a chimp-like knuckle-walking ancestor preceded human bipedalism (for example, ref. However, since the molecular revolution in the 1980–1990s (which provided unequivocal evidence for humans and chimpanzees being sister taxa) 9 a prevalent and influential evolutionary paradigm-said to be based on parsimony-has assumed that the last common ancestor (LCA) of chimpanzees and humans was similar to a modern chimpanzee (for example, ref. ![]() To the contrary, extant apes were seen as extremely specialized animals adapted for below-branch suspension 6, 7. ![]() During the first half of the twentieth century, theories on human evolution were dominated by the view that humans split very early from the common stock of apes, and largely preserved generalized (plesiomorphic) hand proportions similar to other anthropoid primates 6, 7, 8. 1a), which has been related functionally to different selective regimes-manipulation vs locomotion-acting on human and ape hands 1, 5. The human hand can be distinguished from that of apes by its long thumb relative to fingers 1, 2, 3, 4 ( Fig. The hand is one of the most distinctive traits of humankind and one of our main sources of interaction with the environment 1. The human (and australopith) high thumb-to-digits ratio required little change since the LCA, and was acquired convergently with other highly dexterous anthropoids. 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. 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. 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. Human hands are distinguished from apes by possessing longer thumbs relative to fingers.
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