Morphological integration and modularity of the human hand

Morphological modularity is a concept that refers to the level of covariance between the components of a structure. Morphological modules are independent subsets of correlated features; in particular, in the human hand, these are the metacarpus (metapodium) and fingers (acropodium). The human hand has been studied as an integral morphological structure for a long time, but its modularity has not been evaluated within the framework of an integrative approach. The aim of this study is to assess the hypothesis of modularity of the metapodium and acropodium of the human hand in the context of their spatial conjugacy using geometric morphometry. Using geometric morphometric methods to determine the shape and location, both modules were examined in samples from 100 digital X-ray images of the right hands of men and women, using 16 two-dimensional landmarks. The modules were compared using partial least squares analysis and the Escoufier coefficient (RV). Against the background of weak allometric effects (4.6-4.86%, p<0.05), there is a moderate correlation between the blocks of landmarks of the metapodium and acropodium (RV=0.5, p<0.05). Partial Least Squares analysis demonstrates that the shape of the hand is more influenced by the shape of the acropodium, and the change in the shape of the metapodium turned out to be more conservative than that of the acropodium. The observed integration of metapodium and acropodium into human hands in this study indicates the plasticity of the hand, especially its fingers in the context of the diversity of its shape.