A scanning electron microscopic study of hypercementosis

The purpose of this study was to evaluate morphological characteristics of teeth with hypercementosis that are relevant to endodontic practice. Twenty-eight extracted teeth with hypercementosis had their root apexes analyzed by scanning electron microscopy (SEM). The teeth were divided according to tooth groups and type of hypercementosis. The following aspects were examined under SEM: the contour and regularity of the root surface; presence of resorption; presence and number of apical foramina, and the diameter of the main foramen. The progression of club shape hypercementosis was directly associated with the presence of foramina and apical foramen obstruction. Cases of focal hypercementosis presented foramina on the surface, even when sidelong located in the root. Circular cementum hyperplasia form was present in 2 out of 3 residual roots, which was the highest proportion among the tooth types. The detection of a large number of foramina in the apical third of teeth with hypercementosis or even the possible existence of apical foramen obliteration contributes to understand the difficulties faced during endodontic treatment of these cases

Unexpectedly rapid evolution of mandibular shape in hominins

Members of the hominins – namely the so-called ‘australopiths’ and the species of the genus Homo – are known to possess short and deep mandibles and relatively small incisors and canines. It is commonly assumed that this suite of traits evolved in early members of the clade in response to changing environmental conditions and increased consumption of though food items. With the emergence of Homo, the functional meaning of mandible shape variation is thought to have been weakened by technological advancements and (later) by the control over fire. In contrast to this expectation, we found that mandible shape evolution in hominins is exceptionally rapid as compared to any other primate clade, and that the direction and rate of shape change (from the ape ancestor) are no different between the australopiths and Homo. We deem several factors including the loss of honing complex, canine reduction, and the acquisition of different diets may have concurred in producing such surprisingly high evolutionary rates. This study reveals the evolution of mandibular shape in hominins has strong morpho-functional and ecological significance attached

Neurocranium versus Face: A Morphometric Approach with Classical Anthropometric Variables for Characterizing Patterns of Cranial Integration in Extant Hominoids and Extinct Hominins

The relative importance of the two main cranial complexes, the neurocranium and the splanchnocranium, has been examined in the five species of extant hominoids and in a huge sample of extinct hominins using six standard craniometric variables that measure the length, width and height of each cranial module. Factor analysis and two-block partial least squares were used for establishing the major patterns of developmental and evolutionary integration between both cranial modules. The results obtained show that all extant hominoids (including the anatomically modern humans) share a conserved pattern of developmental integration, a result that agrees with previous studies. The pattern of evolutionary integration between both cranial modules in australopiths runs in parallel to developmental integration. In contrast, the pattern of evolutionary and developmental integration of the species of the genus Homo is the opposite, which is probably the consequence of distinctive selective regimes for both hominin groups.JAPC, JMJA and PP received fundings from Ministerio de Ciencia e Innovación, Gobierno de España (http://www.idi.mineco.gob.es), project CGL2011-30334, and Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía, España (http://www.juntadeandalucia.es/organismo​s/economiainnovacioncienciayempleo.html), project P11-HUM-7248 and Research Groups RNM-146 and HUM-607

Extending Epigenesis: From Phenotypic Plasticity to the Bio-Cultural Feedback

The paper aims at proposing an extended notion of epigenesis acknowledging an actual causal import to the phenotypic dimension for the evolutionary diversification of life forms. Section 1 offers introductory remarks on the issue of epigenesis contrasting it with ancient and modern preformationist views. In Section 2 we propose to intend epigenesis as a process of phenotypic formation and diversification a) dependent on environmental influences, b) independent of changes in the genomic nucleotide sequence, and c) occurring during the whole life span. Then, Section 3 focuses on phenotypic plasticity and offers an overview of basic properties (like robustness, modularity and degeneracy) that allows biological systems to be evolvable – i.e. to have the potentiality of producing phenotypic variation. Successively (Section 4), the emphasis is put on environmentally-induced modification in the regulation of gene expression giving rise to phenotypic variation and diversification. After some brief considerations on the debated issue of epigenetic inheritance (Section 5), the issue of culture (kept in the background of the preceding sections) is considered. The key point is that, in the case of humans and of the evolutionary history of the genus Homo at least, the environment is also, importantly, the cultural environment. Thus, Section 6 argues that a bio-cultural feedback should be acknowledged in the “epigenic” processes leading to phenotypic diversification and innovation in Homo evolution. Finally, Section 7 introduces the notion of “cultural neural reuse”, which refers to phenotypic/neural modifications induced by specific features of the cultural environment that are effective in human cultural evolution without involving genetic changes. Therefore, cultural neural reuse may be regarded as a key instance of the bio-cultural feedback and ultimately of the extended notion of epigenesis proposed in this work