Abstract
Inferring the morphology of the last common ancestor of humans, chimpanzees and gorillas is a matter of ongoing debate. Recent findings and reassessment of fossil hominins leads to the hypothesis that the last common ancestor was not extant African ape-like. However, an African great-ape-like ancestor with knuckle walking features still remains plausible and the most parsimonious scenario. Here we address this question via an evolutionary developmental approach, comparing taxon-specific patterns of shape change of the femoral diaphysis from birth to adulthood in great apes, humans, and macaques. While chimpanzees and gorillas exhibit similar locomotor behaviors, our data provide evidence for distinct ontogenetic trajectories, indicating independent evolutionary histories of femoral ontogeny. Our data further indicate that anthropoid primates share a basic pattern of femoral diaphyseal ontogeny that reflects shared developmental constraints. Humans escaped from these constraints via differential elongation of femur.
Highlights
Bipedal locomotion with an upright posture is a defining feature of hominins
Our results further indicates that – apart from taxon-specific differences – there exists a basic pattern of femoral diaphyseal ontogeny that is shared by humans, chimpanzees, gorillas, orangutans, and even Japanese macaques, and that independent of taxon-specific locomotor behaviors and body size
While we focused on differences between humans and great apes in this study, it should be noted that femoral morphology exhibits considerable variation in modern H. sapiens, early H. sapiens, H. neanderthalensis and H. erectus[39,66,67,68,69,70], such that it is likely that diversification of the femoral development should have occurred in our genus Homo
Summary
Bipedal locomotion with an upright posture is a defining feature of hominins (species more closely related to humans than to chimpanzees). A recent comparative study of the proximal femoral morphology of Miocene apes, Orrorin tugenensis, Plio-Pleistocene hominins, and extant hominoids (humans and apes) supports the view that phenotypic variation in extant hominoids is the result of taxon-specific specialization and evolutionary divergence from the primitive state of Miocene apes that is no longer present in extant forms[13]. Amidst these controversies, a central question remains: do the femoral morphologies of chimpanzees and gorillas indicate a knuckle-walking LCA, or do they indicate convergent evolution of knuckle walking from a generalized LCA? The following patterns of variation in femoral morphology and ontogeny are expected in humans, great apes and Japanese macaques for each hypothesis
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