Carolina Paschetta

The Influence of Masticatory Loading on Craniofacial Morphology: A Test Case Across Technological Transitions in the Ohio Valley

Masticatory loading is one of the main environmental stimuli that generate craniofacial variation among recent humans. Experimental studies on a wide variety of mammals, including those with retrognathic postcanine teeth, predict that responses to masticatory loading will be greater in the occlusal plane, the inferior rostrum, and regions associated with the attachments of the temporalis and masseter muscles. Here we test these experimentally-derived predictions on an extinct human population from the middle and upper Ohio valley that underwent a marked shift from hunting-gathering to extensive farming during the last 3,000 years and for which we have good archaeological evidence about diet and food processing technology. Geometric morphometric methods were used to detect and measure the putative effect of diet changes on cranial shape independent of size. Our results partially confirm only some of the experimental predictions. The effect of softer and/or less tough diets on craniofacial shape seem to be concentrated in the relative reduction of the temporal fossa and in a displacement of the attachment of the temporal muscle. However, there were few differences in craniofacial shape in regions closer to the occlusal plane. These results highlight the utility of exploring specific localized morphological shifts using a hierarchical model of craniofacial integration.

Lack of support for the association between facial shape and aggression: a reappraisal based on a worldwide population genetics perspective.

Antisocial and criminal behaviors are multifactorial traits whose interpretation relies on multiple disciplines. Since these interpretations may have social, moral and legal implications, a constant review of the evidence is necessary before any scientific claim is considered as truth. A recent study proposed that men with wider faces relative to facial height (fWHR) are more likely to develop unethical behaviour mediated by a psychological sense of power. This research was based on reports suggesting that sexual dimorphism and selection would be responsible for a correlation between fWHR and aggression. Here we show that 4,960 individuals from 94 modern human populations belonging to a vast array of genetic and cultural contexts do not display significant amounts of fWHR sexual dimorphism. Further analyses using populations with associated ethnographical records as well as samples of male prisoners of the Mexico City Federal Penitentiary condemned by crimes of variable level of inter-personal aggression (homicide, robbery, and minor faults) did not show significant evidence, suggesting that populations/individuals with higher levels of bellicosity, aggressive behaviour, or power-mediated behaviour display greater fWHR. Finally, a regression analysis of fWHR on individuals fitness showed no significant correlation between this facial trait and reproductive success. Overall, our results suggest that facial attributes are poor predictors of aggressive behaviour, or at least, that sexual selection was weak enough to leave a signal on patterns of between- and within-sex and population facial variation.

Developmental and Genetic Constraints on Neurocranial Globularity: Insights from Analyses of Deformed Skulls and Quantitative Genetics

Neurocranial globularity is one of the few derived traits defining anatomically modern humans. Variations in this trait derive from multiple and complex interactions between portions of the brain and the size and shape of the cranial base, among other factors. Given their evolutionary and functional importance, neurocranial globularity is expected to present high genetic and developmental constraints on their phenotypic expression. Here we applied two independent approaches to investigate both types of constraints. First, we assessed if patterns of morphological integration are conserved or else disrupted on a series of artificially deformed skulls in comparison to non-deformed (ND) ones. Second, after the estimation of the genetic covariance matrix for human skull shape, we explored how neurocranial globularity would respond to putative selective events disrupting the normal morphological patterns. Simulations on these deviations were explicitly set to replicate the artificial deformation patterns in order to compare developmental and genetic constraints under the same biomechanical conditions. In general terms, our results indicate that putative developmental constraints help to preserve some aspects of normal morphological integration even in the deformed skulls. Moreover, we find that the response to selection in neurocranial globularity is pervasive. In other words, induced changes in the vault generate a global response, indicating that departures from normal patterns of neurocranial globularity are genetically constrained. In summary, our combined results suggest that neurocranial globularity behaves as a highly genetic and developmental constrained trait.

Nasal airflow simulations suggest convergent adaptation in Neanderthals and modern humans

Significance Due to its role in humidifying and warming the air before it reaches the lungs, adaptations in the internal nasal anatomy are suspected to have been essential for modern humans and Neanderthals during the settlement of Eurasian harsh landscapes. Unfortunately, the lack of soft-tissue evidence in the fossil record precludes any study of Neanderthal respiratory performance. Here, we use warping techniques to reconstruct a generic Neanderthal nose, computational fluid dynamics simulations to compare the respiratory performance on both species, and evolutionary analyses to detect signals of selection. We report striking differences on fluid residence times under cold/dry climatic conditions. Different from previously suggested, our results indicate that both species would have achieved an advantageous species-specific respiratory performance in cold climates. Both modern humans (MHs) and Neanderthals successfully settled across western Eurasian cold-climate landscapes. Among the many adaptations considered as essential to survival in such landscapes, changes in the nasal morphology and/or function aimed to humidify and warm the air before it reaches the lungs are of key importance. Unfortunately, the lack of soft-tissue evidence in the fossil record turns difficult any comparative study of respiratory performance. Here, we reconstruct the internal nasal cavity of a Neanderthal plus two representatives of climatically divergent MH populations (southwestern Europeans and northeastern Asians). The reconstruction includes mucosa distribution enabling a realistic simulation of the breathing cycle in different climatic conditions via computational fluid dynamics. Striking across-specimens differences in fluid residence times affecting humidification and warming performance at the anterior tract were found under cold/dry climate simulations. Specifically, the Asian model achieves a rapid air conditioning, followed by the Neanderthals, whereas the European model attains a proper conditioning only around the medium-posterior tract. In addition, quantitative-genetic evolutionary analyses of nasal morphology provided signals of stabilizing selection for MH populations, with the removal of Arctic populations turning covariation patterns compatible with evolution by genetic drift. Both results indicate that, departing from important craniofacial differences existing among Neanderthals and MHs, an advantageous species-specific respiratory performance in cold climates may have occurred in both species. Fluid dynamics and evolutionary biology independently provided evidence of nasal evolution, suggesting that adaptive explanations regarding complex functional phenotypes require interdisciplinary approaches aimed to quantify both performance and evolutionary signals on covariation patterns.

Shifts in subsistence type and its impact on the human skull's morphological integration

Here we evaluate morphological integration patterns and magnitudes in different skull regions to detect if shifts in morphological integration are correlated to the appearance of more processed (softer) diets.

Developmental pathways inferred from modularity, morphological integration and fluctuating asymmetry patterns in the human face

Facial asymmetries are usually measured and interpreted as proxies to developmental noise. However, analyses focused on its developmental and genetic architecture are scarce. To advance on this topic, studies based on a comprehensive and simultaneous analysis of modularity, morphological integration and facial asymmetries including both phenotypic and genomic information are needed. Here we explore several modularity hypotheses on a sample of Latin American mestizos, in order to test if modularity and integration patterns differ across several genomic ancestry backgrounds. To do so, 4104 individuals were analyzed using 3D photogrammetry reconstructions and a set of 34 facial landmarks placed on each individual. We found a pattern of modularity and integration that is conserved across sub-samples differing in their genomic ancestry background. Specifically, a signal of modularity based on functional demands and organization of the face is regularly observed across the whole sample. Our results shed more light on previous evidence obtained from Genome Wide Association Studies performed on the same samples, indicating the action of different genomic regions contributing to the expression of the nose and mouth facial phenotypes. Our results also indicate that large samples including phenotypic and genomic metadata enable a better understanding of the developmental and genetic architecture of craniofacial phenotypes.

Reply to Evteev and Heuzé: How to overcome the problem of modeling respiration departing from bony structures

Evteev and Heuze (1) state that there is no evidence supporting that Chinese, Japanese, and Korean populations exhibit cold-adaptation features. However, several facial traits present in these groups were previously interpreted as cold-climate adaptations (2⇓⇓⇓⇓⇓⇓–9). For instance, a composite sample that included Chinese, Japanese, and Korean individuals showed internal nasal variation compatible with theoretical expectations for cold climate adaptations (9). It is also noteworthy that we applied computational fluid dynamics (CFD) analyses that directly test for differences in the internal nasal mucosa, making irrelevant any prior difference among cold- versus warm-evolved populations. Such potential prior differences are also irrelevant in the context of Lande’s test, which departs from random … [↵][1]1To whom correspondence may be addressed. Email: rolando{at}cenpat-conicet.gob.ar or rodrigo.r.paz{at}gmail.com. [1]: #xref-corresp-1-1

Canalización e integración morfológica en poblaciones humanas modernas de diferentes contextos culturales y orígenes geográficos/Canalization and morphological integration in modern human populations from different cultural backgrounds and geographic origin

espanolLa teoria evolutiva interpreta el comportamiento humano como adaptativo, es decir, contribuye a maximizar el exito reproductivo de quien lo exhibe. Sin embargo, debido a que la reproduccion implica un costo, aquellos comportamientos que permitan maximizar la relacion entre la produccion de descendientes y la inversion parental serian favorecidos por efecto de la seleccion natural. No obstante, esta relacion estara determinada por las limitaciones impuestas por el ambiente. Por otro lado, la teoria clasica de la transicion demografica sostiene que las mejoras en las condiciones de vida de una poblacion determinan un descenso de la fecundidad. ?Podemos explicar esta relacion desde un punto de vista evolutivo? La poblacion Toba Cacique Sombrero Negro se encuentra en plena transicion economica y social, caracterizada por un mayor sedentarismo y una incipiente economia de mercado. En este trabajo se estiman la Tasa Global de Fecundidad (TGF) y la tasa especifica por edades (fx) de la poblacion rural Toba del oeste de la provincia de Formosa, correspondientes a cuatro periodos entre 1981 y 1999. Se obtuvieron valores crecientes de la TGF que variaron entre 6.36 y 7.27 hijos. La fx evidencio importantes variaciones que determinaron un envejecimiento de las curvas en una primera etapa y un posterior rejuvenecimiento de esta. Se propone aqui que el aumento en la fecundidad estaria determinado por una disminucion de los costos reproductivos maternos, lo que seria el resultado de un mayor acceso a recursos energeticos. Sin embargo, los costos reproductivos pueden variar con la edad materna y por lo tanto, afectando a la estructura etaria de la fecundidad. EnglishAccording to the evolutionary theory, all behaviors should be considered adaptive, i.e., they help to maximize the reproductive success of this actor. However, reproduction involves a cost; thus, natural behaviors that maximize the relationship between the production of offspring and parental investment would be selected. However, this relationship is shaped by the environmental constraints. On the other hand, the classic theory of demographic transition argues that improvements in living conditions in a given population determine a decrease in fertility. Can this observation be explained in evolutionary terms? The population of aboriginal Toba in from Argentina is one undergoing a deep economic and social transition, characterized by a greater availability of material resources. The aim of this study was to evaluate the effect of these socioeconomic changes on several demographic parameters in a population of western Tobas from the province of Formosa, Argentina. This work estimated the Total Fertility Rate (TFR) and age-specific fertility rates (fx) of four periods between 1981-1999. Our results had shown increasing trends of TFR changing between 6.36 and 7.27 children. The peak of fertility changed first to older ages and then changed back to younger ages also. It is proposed that this increase in fertility would be determined by a decrease in maternal reproductive costs, which would be the result of increased access to energy resources. However, these costs can vary with maternal age, affecting the age structure of fertility.RESUMEN Se analizan las relaciones interpoblacionales y los roles relativos cumplidos por las fuerzas evolutivas en la diferenciacion biologica de un conjunto de poblaciones, que habitaron diversas regiones geografico-ecologicas del cono sur sudamericano, con especial atencion a aquellas que ocuparon la region central de Argentina. La muestra esta compuesta por 18 poblaciones, incluyendo 398 adultos masculinos, analizados en 10 variables craneofaciales. Se realizo el analisis de coordenadas principales a partir de distancias D 2 , asi como el analisis de Relethford y Blangero, basado en el modelo de Harpending y Ward para datos morfologicos. El analisis de distancias muestra a Cordoba en una posicion intermedia y relativamente diferenciada de las otras poblaciones, hecho consistente con su ubicacion geografica y que resalta ese factor como condicionante de la evolucion de la poblacion. Por otra parte, muestra similitudes con Santiago del Estero y marcadas diferencias con San Luis, la otra muestra poblacional de las Sierras Centrales. El analisis de Relethford-Blangero permite suponer para Cordoba un tamano efectivo poblacional relativamente grande y la existencia de alto flujo genico, con las poblaciones fuera de la region, mientras que la posicion de San Luis sugiere la accion de fuerzas aleatorias actuando sobre una poblacion pequena. ABSTRACT The aim of this paper is to analyze population relationships and the relative roles fulfilled by the evolutionary forces in the biological differentiation of a group of populations who lived in different geographic -ecological regions of the southern cone of South America, with particular emphasis on those that occupied the central region of Argentina. The sample consists of 18 populations , including 398 adult males , analyzed by ten craniofacial variables . P rincipal coordinates analysis based on D 2 distance and Relethford and Blangero analysis were carried out , based on the model of Harpending and Ward for morphological data. The distance analysis showed Cordoba in an intermediate position and relatively differentiated from the other populations , a fact consistent with its geographical location, that suggests that geography was a conditioning factor in the evolution of the population. On the other hand, Cordoba showed similarities with Santiago del Estero, but with marked differences with San Luis , the other population sample from the Sierras Centrales . The Relethford - Blangero analysis suggests for Cordoba, a relatively large effective population size and the existence of high gene flow with populations outside the region , while the position of San Luis suggests the action of random forces acting on a small isolated population. Publicado on-line: 29/07/2012El objetivo de este trabajo es evaluar el estado de salud oral de una muestra osteologica de origen arqueologico proveniente del sitio Esquina de Huajra, ocupado ca. 1400-1550 A.D. por una poblacion sedentaria y agricultora. Los indicadores considerados fueron el desgaste dental, la presencia de caries, enfermedad periodontal, abscesos y la perdida antemortem de piezas dentales. Se registro la presencia de cada uno de ellos en los 10 individuos que componen la muestra, tanto adultos como subadultos. Presentamos detalladamente la metodologia seguida, especialmente para el registro del desgaste dental. Los mas altos grados de desgaste se observaron en los molares, tal como se esperaria de piezas funcionalmente relacionadas con la masticacion de alimentos duros. Los resultados indicarian el consumo de alimentos ricos en carbohidratos y azucares sin restriccion etaria ni sexual. Tampoco se distinguieron grupos dentro de la muestra que pudieran haber tenido un consumo diferencial de alimentos. Esta homogeneidad concuerda con los resultados obtenidos a partir de los analisis de isotopos estables de C y N, asi como de los estudios del patron funerario.