The modularity of the fingers as a source of morphological variations of the human hand’s shape depending on sex

According to the latest achievements in animal morphology and paleo-morphology, the phenomena of modularity and integration are quite closely interconnected, while morphological integration describes the extent to which various structural features are related to each other in the process of morphogenesis, while modularity reflects the rate of evolutionary transformation, which determines the degree of this conjugation. One of the classical objects of study of modularity and integration in morphology is regularly segmented skeletal structures, in particular, the hand. In humans, the hand is characterized mainly by the ratio of the lengths of the index and ring fingers, while their position and the value that determines the structure of the hand as a whole in the space of its shape has not yet been studied. In this paper, the influence of the modules of the fingers on the shape of the hand in the framework of their morphological integration was determined, which became the main goal of the study. The method of geometric morphometry of digital images of radiographs of the right hands of 100 people was used, on which the coordinates of 16 landmarks of the phalanges of the II-V fingers were determined, followed by a study of the shape, covariance and modularity. The results showed that changes in the shape of the hand are due to the position of the II-V fingers in space, with the ulnar type of the hand (2d4d) reverse transformations in space are observed. The position of the second finger in space largely affects the shape of the hand as a whole. An analysis of the modularity of the fingers indicates a significant integration between them, compared with the integration of other modules of the hand. The high values of covariance revealed as a result of the study in pairwise comparison of the modules of the fingers and lower values of covariance in the multiple comparison between the modules of the hand indicate a different degree of local influence of morphogenetic factors on the structural features and shape of the hand in people of different sexes.