Abstract
Mosaic evolution is a key mechanism that promotes robustness and evolvability in living beings. For the human head, to have a modular organization would imply that each phenotypic module could grow and function semi-independently. Delimiting the boundaries of head modules, and even assessing their existence, is essential to understand human evolution. Here we provide the first study of the human head using anatomical network analysis (AnNA), offering the most complete overview of the modularity of the head to date. Our analysis integrates the many biological dependences that tie hard and soft tissues together, arising as a consequence of development, growth, stresses and loads, and motion. We created an anatomical network model of the human head, where nodes represent anatomical units and links represent their physical articulations. The analysis of the human head network uncovers the presence of 10 musculoskeletal modules, deep-rooted in these biological dependences, of developmental and evolutionary significance. In sum, this study uncovers new anatomical and functional modules of the human head using a novel quantitative method that enables a more comprehensive understanding of the evolutionary anatomy of our lineage, including the evolution of facial expression and facial asymmetry.
Highlights
Anatomical networks reveal the musculoskeletal modularity of the human head Borja Esteve-Altava[1], Rui Diogo[2], Christopher Smith[2], Julia C
To have a modular organization would imply that each phenotypic module could grow and function semi-independently
We provide the first study of the human head using anatomical network analysis (AnNA), offering the most complete overview of the modularity of the head to date
Summary
Anatomical networks reveal the musculoskeletal modularity of the human head Borja Esteve-Altava[1], Rui Diogo[2], Christopher Smith[2], Julia C. A recent anatomical network analysis (AnNA) showed that functional matrices are essential to generate a proper pattern of connectivity of the face, whereas the pressure of the growing brain against the skull vault is not necessary to explain the connectivity pattern among the bones of the cranial vault and base[15] We use this new quantitative and objective approach (AnNA) to treat the skeletal, cartilaginous, and muscular units of the human head as the elements of a network (nodes), whose interactions at their physical contacts (links) determine the boundaries of the phenotypic modules of the head (Fig. 1 and Table 1; see Methods and SI for further details). The laryngeal musculoskeletal complex (module 3) constitutes a well-defined phenotypic module that includes the laryngeal cartilages
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