Violation of Dollo's Law: Evidence of Muscle Reversions in Primate Phylogeny and Their Implications for the Understanding of the Ontogeny, Evolution, and Anatomical Variations of Modern Humans

Abstract

According to Dollo's law, once a complex structure is lost it is unlikely to be reacquired. In this article, we report new data obtained from our myology‐based cladistic analyses of primate phylogeny, which provide evidence of anatomical reversions violating Dollo's law: of the 220 character state changes unambiguously optimized in the most parsimonious primate tree, 28 (13%) are evolutionary reversions, and of these 28 reversions six (21%) occurred in the nodes that lead to the origin of modern humans; nine (32%) violate Dollo's law. In some of these nine cases, the structures that were lost in adults of the last common ancestor and are absent in adults of most subgroups of a clade are actually present in early ontogenetic stages of karyotypically normal individuals as well as in later ontogenetic stages of karyotypically abnormal members of those subgroups. Violations of Dollo's law may thus result from the maintenance of ancestral developmental pathways during long periods of trait absence preceding the reacquisition of the trait through paedomorphic events. For instance, the presence of contrahentes and intermetacarpales in adult chimpanzees is likely due to a prolonged/delayed development of the hand musculature, that is, in this case chimpanzees are more neotenic than modern humans.

Are there general laws for digit evolution in squamates? The loss and re‐evolution of digits in a clade of fossorial lizards (Brachymeles, Scincinae)

“…This phylogenetic evidence is corroborated with osteological and myological data, which show that the pentadactyl forelimb in Brachymeles exists in a structurally less complex form with fewer phalanges and fewer muscles, at least in B. kadwa , than what is typical of other pentadactyl skinks. Our data are consistent with Dollo's law, as Dollo himself meant it, and we show that although complex structures once lost (i.e., digits), can re‐evolve, they do not re‐evolve in the same form as the ancestral state (but see Diogo & Wood, ). As a test of Morse's law, we investigated the order of digit reduction established during the processes of digit loss in Brachymeles .…”

Is evolutionary biology becoming too politically correct? A reflection onthe scala naturae, phylogenetically basal clades, anatomically plesiomorphic taxa, and ‘lower’ animals

“…As noted in Diogo & Wood (2012b, reversions played a substantial role in primate and human evolution because 1 in 7 of the 220 evolutionary transitions unambiguously optimized in their most parsimonious primate phylogenetic tree (concerning changes in the head, neck, pectoral and forelimb musculature) are reversions to a plesiomorphic state. As noted in Diogo & Wood (2012b, reversions played a substantial role in primate and human evolution because 1 in 7 of the 220 evolutionary transitions unambiguously optimized in their most parsimonious primate phylogenetic tree (concerning changes in the head, neck, pectoral and forelimb musculature) are reversions to a plesiomorphic state.…”

Dinosaurs, Chameleons, Humans, and Evo‐Devo Path: Linking Étienne Geoffroy's Teratology, Waddington's Homeorhesis, Alberch's Logic of “Monsters,” and Goldschmidt Hopeful “Monsters”

“…, , )—evo‐devo‐P'Anth in addition also pays a special attention to data obtained from biological and physical anthropology. For instance, it pays attention to information on the specific evolutionary changes, including convergences, parallelisms, and reversions of the muscles in each major extant primate group, and to the evolutionary rates within these transformations (e.g., Diogo and Wood, ; Diogo and Wood, ; Diogo and Wood, ; Diogo and Wood, ; Diogo and Molnar, ; Diogo and Wood, ).…”

“…An example given by Minelli concerns the fourth pair of legs in the mites: the legs are present in the embryo, lacking in the larval instar, and then present in the nymphal and adult stages of most mites. Importantly, the platysma cervicale, contrahentes digitorum, and intermetacarpales of karyotypically “normal” human embryos do not correspond to the muscles of adult primates such as chimpanzees or of other adult mammals as predicted by Haeckel's recapitulation: they correspond instead to the muscles of the embryos of those taxa (Diogo and Wood, , ). The developmental pathways resulting in the presence of these muscles in adults of those taxa were not completely lost in modern humans, even after several million years, likely because these pathways are associated (e.g., pleiotropy) with those recruited in the formation of other structures that are present and functional in modern human adults.…”