ABSTRACT
The results of Diogo and Wood (2012a,b) concerning evolutionary reversions in primates and their closest living relatives are summarized in the tree in Fig. 6.1. These results suggest that evolutionary reversions played a substantial role in primate and human evolution, at least with respect to the musculature of the head and neck, pectoral region, and upper limb. One in seven of the 220 evolutionary transitions that are unambiguously optimized in this tree is a reversion to a plesiomorphic state (N = 28). Of the 28 reversions shown in this tree, six occurred at nodes that led to the origin of modern humans (Fig. 6.1). One occurred at the node leading to the Hominoidea (q’: reversion of “Temporalis has a pars suprazygomatica”), one at the node leading to the Homininae (t’: reversion of “Latissimus dorsi and teres major are fused”), and four occurred within the sub-tribe Hominina (y’, z’, C’ and D’: reversions of “Anterior portion of sternothyroideus extends anteriorly to the posterior portion of the thyrohyoideus”, “Rhomboideus major and rhomboideus minor are not distinct muscles”, “Tendon of fl exor digitorum profundus to digit 1 is vestigial or absent”, and “Flexor carpi radialis originates from the radius”; NB, the genus Pan is included in the other Hominini sub-tribe, the Panina).
