Sobre el uso de los mínimos cuadrados parciales de dos bloques para el estudio de los patrones integración entre el neurocráneo y el esplacnocráneo en homínidos actuales y homínidos extintos

Abstract

Many biological structures that interact in development and/or function tend to evolve in a concertedly fashion and thus become integrated forming modules. The two most prominent modules of the mammalian cranium are the cerebral capsule (i.e., the neurocranium) and the face (i.e., the splanchnocranium), as inferred from both developmental processes and functional reasons. The relative importance of both cranial complexes was estimated here by means of their relative sizes, which were measured in the five extant hominoid species and also in a huge sample of extinct hominins using six standard cranial measurements as proxies of the length, width, and height of each cranial module. Several two-block partial least-squares analyses (2B-PLS) were performed for adults of the extant and extinct species using size standardized and non-standardized variables, as well as pooled and non-pooled within-species correlation matrices. When no size standardization was performed, pooled and non pooled within-species analyses showed a common pattern of developmental integration for all living hominoid species, on the one hand, and very different patterns of evolutionary integration, on the other, in which each species exhibited a distinct relationship between the relative sizes of their modules. On the contrary, when cranial size was removed, ontogenetic and evolutionary integration run in the same direction, which indicates that the relative sizes of the splanchnocranium and the neurocranium relate inversely both within and between species. Australopiths, the extinct representatives of the genus Homo and the anatomical modern humans (AMH) seem to lie in a different trend than the great apes, although the pattern of covariation between their cranial modules is basically the same. This difference suggests that a great ape cannot reach the morphology of an AMH simply by increasing the size of its neurocranium. Similarly, an AMH cannot be transformed to the face/neurocranium proportions of an ape simply by reducing its neurocranium. We thank the Universidad de Malaga. Campus de Excelencia Internacional Andalucia Tech and the Ministerio de Ciencia e Innovacion (Ref. CGL2011-30334).