Shape Ontogeny of the Distal Femur in the Hominidae with Implications for the Evolution of Bipedality (original) (raw)
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Rapid morphological change in living humans: implications for modern human …
Comparative Biochemistry and Physiology-Part A: …
Human body size and body proportions are interpreted as markers of ethnicity, 'race,' adaptation to temperature, nutritional history and socioeconomic status. Some studies emphasize only one of these indicators and other studies consider combinations of indicators. To better understand the biocultural nature of human size and proportions a new study of the growth of Maya-American youngsters was undertaken in 1999 and 2000. One purpose of this research is to assess changes in body proportion between Maya growing up in the US and Maya growing up in Guatemala. Height and sitting height of 6-12-year-old boys and girls (ns360) were measured and the sitting height ratio wsitting heighty heightx=100, a measure of proportion, was calculated. These data are compared with a sample of Maya of the same ages living in Guatemala and measured in 1998 (ns1297). Maya-American children are currently 10.24 cm taller, on average, and have a significantly lower sitting height ratio, (i.e. relatively longer legs, averaging 7.02 cm longer) than the Guatemala Maya. Maya-American children have body proportions more like those of white children in the US than like Maya children in Guatemala. Improvements in the environment for growth, in terms of nutrition and health, seem to explain both the trends in greater stature and relatively longer legs for the Maya-Americans. These findings are applied to the problem of modern human origins as assessed from fossil skeletons. It has been proposed that heat adapted, relatively long-legged Homo sapiens from Africa replaced the cold adapted, relatively short-legged Homo neandertalensis of the Levant and Europe wJ Hum Evol 32 (1997a) 423x. Skeletal samples of Maya adults from rural Guatemala have body proportions similar to adult Neandertals and to skeletal samples from Europe with evidence of nutritional and disease stress. Just as nutrition and health status explains the differences in the body proportions of living Maya children, these factors, along with adaptation to climate, may also explain much of the differences between the Neandertal and African hominid samples. ᮊ
Rapid morphological change in living humans: implications for modern human origins
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2003
Human body size and body proportions are interpreted as markers of ethnicity, 'race,' adaptation to temperature, nutritional history and socioeconomic status. Some studies emphasize only one of these indicators and other studies consider combinations of indicators. To better understand the biocultural nature of human size and proportions a new study of the growth of Maya-American youngsters was undertaken in 1999 and 2000. One purpose of this research is to assess changes in body proportion between Maya growing up in the US and Maya growing up in Guatemala. Height and sitting height of 6-12-year-old boys and girls (ns360) were measured and the sitting height ratio wsitting heighty heightx=100, a measure of proportion, was calculated. These data are compared with a sample of Maya of the same ages living in Guatemala and measured in 1998 (ns1297). Maya-American children are currently 10.24 cm taller, on average, and have a significantly lower sitting height ratio, (i.e. relatively longer legs, averaging 7.02 cm longer) than the Guatemala Maya. Maya-American children have body proportions more like those of white children in the US than like Maya children in Guatemala. Improvements in the environment for growth, in terms of nutrition and health, seem to explain both the trends in greater stature and relatively longer legs for the Maya-Americans. These findings are applied to the problem of modern human origins as assessed from fossil skeletons. It has been proposed that heat adapted, relatively long-legged Homo sapiens from Africa replaced the cold adapted, relatively short-legged Homo neandertalensis of the Levant and Europe wJ Hum Evol 32 (1997a) 423x. Skeletal samples of Maya adults from rural Guatemala have body proportions similar to adult Neandertals and to skeletal samples from Europe with evidence of nutritional and disease stress. Just as nutrition and health status explains the differences in the body proportions of living Maya children, these factors, along with adaptation to climate, may also explain much of the differences between the Neandertal and African hominid samples. ᮊ
Journal of Human Evolution, 2023
Previous studies showed that there is variation in ontogenetic trajectories of human limb dimensions and proportions. However, little is known about the evolutionary significance of this variation. This study used a global sample of modern human immature long bone measurements and a multivariate linear mixed-effects model to study 1) whether the variation in ontogenetic trajectories of limb dimensions is consistent with ecogeographic predictions and 2) the effects of different evolutionary forces on the variation in ontogenetic trajectories. We found that genetic relatedness arising from neutral (nonselective) evolution, allometric variation associated with the change in size, and directional effects from climate all contributed to the variation in ontogenetic trajectories of all major long bone dimensions in modern humans. After accounting for the effects of neutral evolution and holding other effects considered in the current study constant, extreme temperatures have weak, positive associations with diaphyseal length and breadth measurements, while mean temperature shows negative associations with diaphyseal dimensions. The association with extreme temperatures fits the expectations of ecogeographic rules, while the association with mean temperature may explain the observed among-group variation in intralimb indices. The association with climate is present throughout ontogeny, suggesting an explanation of adaptation by natural selection as the most likely cause. On the other hand, genetic relatedness among groups, as structured by neutral evolutionary factors, is an important consideration when interpreting skeletal morphology, even for nonadult individuals.
DEVELOPMENTAL BIOLOGY AND HUMAN EVOLUTION
Annual Review of Anthropology, 2003
Key Words bone, hominid, developmental fields, mechanical loading, limb patterning s Abstract Our understanding of developmental biology burgeoned during the last decade. This review summarizes recent advances, provides definitions and explanations of some basic principles, and does so in a way that will aid anthropologists in understanding their profound implications. Crucial concepts, such as developmental fields, selector and realizator genes, cell signaling mechanisms, and gene regulatory elements are briefly described and then integrated with the emergence of skeletal morphology. For the postcranium, a summary of events from limb bud formation, the appearance of anlagen, the expression of Hox genes, and the fundamentals of growth plate dynamics are briefly summarized. Of particular importance are revelations that bony morphology is largely determined by pattern formation, that growth foci such as physes and synovial joints appear to be regulated principally by positional information, and that variation in these fields is most likely determined by cis-regulatory elements acting on restricted numbers of anabolic genes downstream of selectors (such as Hox). The implications of these discoveries for the interpretation of both contemporary and ancient human skeletal morphology are profound. One of the most salient is that strain transduction now appears to play a much reduced role in shaping the human skeleton. Indeed, the entirety of "Wolff's Law" must now be reassessed in light of new knowledge about pattern formation. The review concludes with a brief discussion of some implications of these findings, including their impact on cladistics and homology, as well as on biomechanical and morphometric analyses of both ancient and modern human skeletal material.
Journal of Human Evolution
This study addresses how the human temporal bone develops the population-specific pattern of morphology observed among adults and at what point in ontogeny those patterns arise. Three-dimensional temporal bone shape was captured using 15 landmarks on ontogenetic series of specimens from seven modern human populations. Discriminant function analysis revealed that population-specific temporal bone morphology is evident early in ontogeny, with significant shape differences among many human populations apparent prior to the eruption of the first molar. As early as five years of age, temporal bone shape reflects population history and can be used to reliably sort populations, although those in closer geographic proximity and molecular affinity are more likely to be misclassified. The deviation of cold-adapted populations from this general pattern of congruence between temporal bone morphology and genetic distances, identified in previous work, was confirmed here in adult and subadult specimens, and was revealed to occur earlier in ontogeny than previously recognized. Significant differences exist between the ontogenetic trajectories of some pairs of populations, but not among others, and the angles of these trajectories do not reflect genetic relationships or final adult temporal bone size. Significant intrapopulation differences are evident early in ontogeny, with differences becoming amplified by divergent trajectories in some groups. These findings elucidate how the congruence between adult human temporal bone morphology and population history develops, and reveal that this pattern corresponds closely to that described previously for facial ontogeny.
2011
Objectives: Adult population differences in relative and absolute limb size often are explained as adaptations to different climates. Less is known about other aspects of limb bone form and their population-specific growth patterns. Methods: We study postnatal ontogenetic development of tibial and femoral form by a multivariate morphometric approach in a cross-sectional sample of South African (N = 97) and European (N = 81) modern humans from 0 to 20 years of age. Because the epiphyses ossify and fuse to the diaphysis in this time period, we separately analyze two sets of variables. Average ontogenetic trajectories are computed to compare the growth patterns of the African and the European groups. Results: For both the tibia and the femur, we could show that Africans and Europeans have a very similar average length and average shape until about 10 years of age. During adolescence Africans have a higher growth rate leading to longer adult bones with narrower epiphyses relative to the diaphysis. Despite substantial individual overlap, the average crural index is higher in Africans than in Europeans, from birth on through adulthood. Conclusions: The prenatal origin of population differences in the crural index indicates a genetic determination of these differences whereas limb length and relative epiphyseal width likely are both genetically and environmentally determined.
Femur ontogeny in humans and great apes: heterochronic implications for hominid évolution
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1997
Did the first hominids have a short developmental period similar to that of the great apes, or a longer period closer to that of modern humans? Some morphological modifications undergone by the human femur during growth are shown to be excellent markers of different developmental stages. The femur of the first hominids (Australopithecus afarensis> shows only features of infantile growth, whereas characters of both infantile and adolescent growth are typical of later hominids (Homo). In the first australopithecines the period of peripubertal growth would have still been short. The prolongation of the adolescent period appears to be a characteristic of Homo.
The shape of human evolution: A geometric morphometrics perspective
Evolutionary Anthropology: Issues, News, and Reviews, 2012
Study of morphological form is fundamental to the discipline of paleoanthropology. The size and shape of our ancestors' anatomical features have long been the focus of research on hominin systematics, phylogeny, functional morphology, ontogeny, variation, and evolutionary change. Early physical anthropologists relied on both qualitative descriptions of anatomical shape and linear measurements to assess variation among hominins. The seminal works of W. W. Howells 1 and C. E. Oxnard 2 helped to bring multivariate techniques to the forefront of physical anthropology. Howells' intention was the objective delineation of components of shape, which could then fuel further analyses and interpretations, as well as clarification of the ways that growth influences interindividual and interpopulational differences in shape. He expressed concern that previous comparisons of individual measurements did not capture the overall shape of the skull, which is ''expressed by the relations between measurements.'' 1:3 Similarly, Oxnard recognized that a multivariate approach to the study of complex shapes allows ''for such perturbations (e.g., variation and covariation). . .that are difficult to evaluate by eye and impossible to reveal by measurement and simple analysis alone.'' 2:6 While multivariate methods offered clear advantages over univariate or bivariate representations of shape, the analysis of traditional morphometric measures such as linear distances, angles, and ratios, has limitations when it comes to quantifying the complex geometry of some anatomical structures.
PeerJ, 2022
This article studies the evolutionary change of allometries in the relative size of the two main cranial modules (neurocranium and splanchnocranium) in the five living hominid species and a diverse sample of extinct hominins. We use six standard craniometric variables as proxies for the length, width and height of each cranial module. Factor analysis and two-block partial least squares (2B-PLS) show that the great apes and modern humans share a pervasive negative ontogenetic allometry in the neurocranium and a positive one in the splanchnocranium. This developmental constraint makes it possible to interpret the cranial heterochronies in terms of ontogenetic scaling processes (i.e., extensions or truncations of the ancestral ontogenetic trajectory) and lateral transpositions (i.e., parallel translations of the entire trajectory starting from a different shape for a given cranial size). We hypothesize that ontogenetic scaling is the main evolutionary modality in the australopithecines while in the species of Homo it is also necessary to apply transpositions. Both types of processes are coordinated in Homo, which result in an evolutionary trend toward an increase in brain size and in the degree of paedomorphosis from the earliest habilines.