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Abstract ObjectivesModular architecture of traits in complex organisms can be important for morphological evolution at micro‐ and sometimes macroevolutionary scales as it may influence the tempo and direction of changes to groups of traits that are essential for particular functions, including food acquisition and processing. We tested several distinct hypotheses about craniofacial modularity in the hominine skull in relation to feeding biomechanics. Materials and MethodsFirst, we formulated hypothesized functional modules for craniofacial traits reflecting specific demands of feeding biomechanics (e.g., masseter leverage/gape or tooth crown mechanics) inHomo sapiens,Pan troglodytes, andGorilla gorilla. Then, the pattern and strength of modular signal was quantified by the covariance ratio coefficient and compared across groups using covariance ratio effect size. Hierarchical clustering analysis was then conducted to examine whether a priori‐defined functional modules correspond to empirically recovered clusters. ResultsThere was statistical support for most a priori‐defined functional modules in the cranium and half of the functional modules in the mandible. Modularity signal was similar in the cranium and mandible, and across the three taxa. Despite a similar strength of modularity, the empirically recovered clusters do not map perfectly onto ourpriorifunctional modules, indicating that further work is needed to refine our hypothesized functional modules. ConclusionThe results suggest that modular structure of traits in association with feeding biomechanics were mostly shared with humans and the two African apes. Thus, conserved patterns of functional modularity may have facilitated evolutionary changes to the skull during human evolution.
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Functional morphological integration related to feeding biomechanics in the hominine skull
Quantifying and characterizing the pattern of trait covariances is crucial for understanding how population-level patterns of integration might constrain or facilitate craniofacial evolution related to the feeding system. This study addresses an important gap in our knowledge by investigating magnitudes and patterns of morphological integration of biomechanically informative traits in the skulls of Homo sapiens, Pan troglodytes, and Gorilla gorilla. We predicted a lower magnitude of integration among human biomechanical traits since humans eat a softer, less biomechanically challenging diet than apes. Indeed, compared to African apes, the magnitudes of integration were lower in H. sapiens skulls for form data (raw dimensions) but were similar or higher for shape data (raw dimensions scaled by geometric mean). Patterns of morphological integration were generally similar, but not identical, across the three species, particularly for the form data compared to the shape data. Traits that load heavily on the primary axis of variation in morphospace are generally associated with size and/or shape of the temporalis and masseter muscles and with dimensions related to the constrained lever model of jaw biomechanics. Given the conserved nature of morphological integration, skull adaptations for food processing in African apes and humans may have been constrained to occur along certain paths of high evolvability. The conserved pattern of functional integration also indicates that extant hominine species can operate as reasonable analogues for extinct hominins in studies that require population-level patterns of trait variance/covariance.
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- Award ID(s):
- 2019669
- PAR ID:
- 10478277
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of Human Evolution
- Volume:
- 182
- Issue:
- C
- ISSN:
- 0047-2484
- Page Range / eLocation ID:
- 103401
- Subject(s) / Keyword(s):
- Morphological covariation Evolvability statistics Morphological evolution Evolution of cranio-mandibular architecture Quantitative genetics
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.jhevol.2023.103401
