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Hominin Evolution (hominin + evolution)
Selected AbstractsDirect Male Care and Hominin Evolution: Why Male,Child Interaction Is More Than a Nice Social IdeaAMERICAN ANTHROPOLOGIST, Issue 1 2010Lee T. Gettler ABSTRACT, Early members of the genus Homo experienced heightened absolute metabolic costs, partially owing to increases in body size. However, as is characteristic of modern humans, they also likely began reproducing with shortened interbirth intervals. Male investment in offspring may help explain how this life history shift occurred. Evolutionary models of hominin male investment in offspring have traditionally focused on provisioning of females and young, yet the extent to which direct male care of offspring was evolutionarily important, from an energetic perspective, is largely unaddressed. I propose an evolutionary model of direct male care, demonstrating that males could have helped reduce the energetic burden of caregiving placed on mothers by carrying young. In doing so, males would have assisted females in achieving and maintaining an energetic condition sufficient for reproduction, thereby hastening the advent of shortened interbirth intervals that played a formative role in the success of our genus. [source] Docosahexaenoic acid, the aquatic diet, and hominin encephalization: Difficulties in establishing evolutionary linksAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 1 2007Bryce A. Carlson Distinctive characteristics of modern humans, including language, tool manufacture and use, culture, and behavioral plasticity, are linked to changes in the organization and size of the brain during hominin evolution. As brain tissue is metabolically and nutritionally costly to develop and maintain, early hominin encephalization has been linked to a release of energetic and nutritional constraints. One such nutrient-based approach has focused on the n -3 long-chained polyunsaturated fatty acid docosahexaenoic acid (DHA), which is a primary constituent of membrane phospholipids within the synaptic networks of the brain essential for optimal cognitive functioning. As biosynthesis of DHA from n -3 dietary precursors (alpha-linolenic acid, LNA) is relatively inefficient, it has been suggested that preformed DHA must have been an integral dietary constituent during evolution of the genus Homo to facilitate the growth and development of an encephalizing brain. Furthermore, preformed DHA has only been identified to an appreciable extent within aquatic resources (marine and freshwater), leading to speculation that hominin encephalization is linked specifically to access and consumption of aquatic resources. The key premise of this perspective is that biosynthesis of DHA from LNA is not only inefficient but also insufficient for the growth and maturation demands of an encephalized brain. However, this assumption is not well-supported, and much evidence instead suggests that consumption of LNA, available in a wider variety of sources within a number of terrestrial ecosystems, is sufficient for normal brain development and maintenance in modern humans and presumably our ancestors. Am. J. Hum. Biol. 19:132,141, 2007. © 2006 Wiley-Liss, Inc. [source] Morphometric variation in the papionin muzzle and the biochronology of the South African Plio-Pleistocene karst cave depositsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2010Christopher C. Gilbert Abstract Papionin monkeys are widespread, relatively common members of Plio-Pleistocene faunal assemblages across Africa. For these reasons, papionin taxa have been used as biochronological indicators by which to infer the ages of the South African karst cave deposits. A recent morphometric study of South African fossil papionin muzzle shape concluded that its variation attests to a substantial and greater time depth for these sites than is generally estimated. This inference is significant, because accurate dating of the South African cave sites is critical to our knowledge of hominin evolution and mammalian biogeographic history. We here report the results of a comparative analysis of extant papionin monkeys by which variability of the South African fossil papionins may be assessed. The muzzles of 106 specimens representing six extant papionin genera were digitized and interlandmark distances were calculated. Results demonstrate that the overall amount of morphological variation present within the fossil assemblage fits comfortably within the range exhibited by the extant sample. We also performed a statistical experiment to assess the limitations imposed by small sample sizes, such as typically encountered in the fossil record. Results suggest that 15 specimens are sufficient to accurately represent the population mean for a given phenotype, but small sample sizes are insufficient to permit the accurate estimation of the population standard deviation, variance, and range. The suggestion that the muzzle morphology of fossil papionins attests to a considerable and previously unrecognized temporal depth of the South African karst cave sites is unwarranted. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source] Relationship between formation of the femoral bicondylar angle and trochlear shape: Independence of diaphyseal and epiphyseal growthAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2006C. Tardieu Abstract During hominin evolution, an increase in the femoral bicondylar angle was the initial change that led to selection for protuberance of the lateral trochlear lip and the elliptical profile of the lateral condyle. No correlation is found during ontogeny between the degree of femoral obliquity and of the prominence of the lateral trochlear lip. Might there be a relationship with the elliptical profile of the lateral condyle? On intact femoral diaphyses of juvenile humans and great apes, we compared the anteroposterior length of the lateral and medial sides of the distal metaphysis. The two diaphyseal pillars remain equal during postnatal growth in great apes, while the growth of the lateral pillar far exceeds that of the medial pillar in humans. Increase in bicondylar angle is correlated with disproportionate anteroposterior lengthening of the lateral pillar. The increased anteroposterior length of the lateral side of the metaphysis would contribute to increasing the radius of the curvature of the lateral condyle, but not to the projection of the lateral trochlear lip. The similar neonatal and adult femoro-patellar joint shape in humans prompted an assessment of the similarity during growth of the entire neonatal and adult epiphyses. We showed that the entire epiphysis undergoes drastic changes in proportions during postnatal growth. Finally, we emphasize the need to distinguish the cartilaginous phenotype and the ossified phenotype of the distal femoral epiphysis (and of any epiphysis) during postnatal growth. This crucial distinction applies to most postcranial bones, for they almost all develop following the process of endochondral ossification. Am J Phys Anthropol, 2006. © 2006 Wiley-Liss, Inc. [source] | ||||||||||