The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Comparative anatomy, evolutionary trends and the myth of human morphological complexity: empirical studies reveal that modern humans have fewer muscles than most primate and non-primate mammals


1Anatomy, Howard University College of Medicine, 2Anatomy, Valladolid University, 3Anthropology, Center For the Study of Hominid Paleobiology, GWU

Saturday 1:30-1:45, Galleria North Add to calendar

We undertook gross anatomical dissections of the soft tissues of various individuals from each major primate clade (total N = 55). The results obtained from these dissections and from our cladistic analyses may seem paradoxical. On the one hand the cladistic analyses suggest there is a higher number of unambiguous evolutionary steps [NS] from the base of the tree to modern humans than to any other taxon included in the study. Yet our anatomical studies reveal that modern humans have fewer muscles than most other mammals and than most primates, in particular many fewer than in strepsirrhine and tarsiiform primates. For instance, Nycticebus has a NS of 30 and a range of 133-139 head, neck, pectoral and upper limb muscles in total, while modern humans have an NS of 75 but only 123 muscles in total and chimpanzees have an NS of 70, but have 3 more muscles than modern humans in total. The solution to this apparent paradox lies on Stephen J. Gould's contention that the importance given to 'evolutionary trends’ and particularly to the supposed examples of human remarkable morphological complexity is best explained by the historical under-reporting of examples of undirected evolution and of morphological 'simplification'. That is, despite accumulating more evolutionary transitions than other primates, these transitions did not result in modern humans having more muscles or bundles per muscle, e.g. since the Pan/Homo split humans have actually secondarily lost muscles (e.g., levator claviculae and dorsoepitrochlearis) that are present in most other primates.

We gratefully acknowledge the support of the Dean of HU College of Medicine and the Senior Vice President for Health Sciences of HU, as well as the GW Signature Program, the GW Provost, and the Mathers Foundation.

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