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Population Affinities of the Jebel Sahaba Skeletal Sample (Holliday 2013)
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[QUOTE]Originally posted by the lioness,: [QB] [QUOTE]Originally posted by Troll Patrol: The authors are wiping the floor with C. Coon's theories. Leg Length, Body Proportion, and Health: A Review with a Note on Beauty Barry Bogin and Maria Inęs Varela-Silva http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872302/ [/QB][/QUOTE][b]Leg Length, Body Proportion, and Health: A Review with a Note on Beauty Barry Bogin and Maria Inęs Varela-Silva Coon divided living peoples of the world into five “races” based, in part, on body size and proportions. The Australian Aborigines (designated “Australoids” by Coon), have exceptionally long legs in proportion to stature, and African pygmies (“Congoids” in Coon’s taxonomy), have exceptionally short stature, long arms relative to leg length, and especially short lower legs. Coon’s claim that African pygmies have “achondroplastic proportions” is also wrong. Shea and Bailey show that African pygmies are reduced in overall size and have a body shape that is allometrically proportional to the size reduction.[/b] _____________________________________________ Isometric scaling occurs when changes in size (during growth or over evolutionary time) do not lead to changes in proportion. Allometric scaling is any change that deviates from isometry. A classic example is the skeleton of mammals, which becomes much more robust and massive relative to the size of the body as the body size increases. Eskimos and Pygmies have legs that are shorter than non-Pygmy Africans. Coon said in pygmies it was due to achondroplasia. Achondroplasiais a common cause of dwarfism. It occurs as a sporadic mutation in approximately 75% of cases (associated with advanced paternal age) or may be inherited as an autosomal dominant genetic disorder. In the above article Bogin says Shea and Bailey say their short legs would a change in proportion due to their smaller size (Bergman's rule) ___________________________________________ [b]Leg Length, Body Proportion, and Health: A Review with a Note on Beauty Barry Bogin and Maria Inęs Varela-Silva The human species is distinguished from the non-human primates by several anatomical features. Among these are proportions of the arms and legs relative to total body length. The human difference is illustrated in Figure 5. In proportion to total body length, measured as stature, modern human adults have relatively long legs and short arms. Quantitative differences between adult humans, chimpanzees (Pan troglodytes), and bonobos The primary reason for this is human bipedal locomotion, a behavior which evolved at least by 4.4 million years ago (MYA), as shown in the fossil hominin species Ardipithecus ramidus. Leg length must approximate 50 percent of total stature to achieve the biomechanical efficiency of the human striding bipedal gait. The sitting height ratio (SHR) is a commonly used measure of body proportion. Measured stature minus sitting height may also be used to estimate leg length but this measure does not standardize for total height making it difficult to compare individuals with different statures. Mean SHR for populations of adults varies from minimum values, i.e., relatively longest legs, for Australian Aborigines (SHR = 47.3 for men and 48.1 for women) to the maximum SHR values, i.e., relatively shortest legs, for Guatemala Maya men and Peruvian women (SHR = 54.6 and 55.8). Two well-known ecogeographic principles, Bergmann’s and Allen’s Rules, are often cited as primary causes for the global patterns of human body shape variation. Large body mass and relatively short extremities increase the ratio of volume-to-surface area and provide for a body shape that maximizes metabolic heat retention in a mammal. Conversely, in warmer temperatures, relative long extremities increases surface areas relative to volume and allows for greater heat loss. It has been shown experimentally that mice and other non-human mammals raised in warmer temperature experience greater bone tissue growth and longer limb bones (Serrat MA, King D, Lovejoy CO. Temperature regulates limb length in homeotherms by directly modulating cartilage growth.) Bergmann’s and Allen’s rules apply, to some extent, to the human species. These climate relationships, however, are not perfect. A re-analysis of the Roberts’ data by Katzmarzyk and Leonard [The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.Destroy user interface control52] modifies the importance of climate as the primary molder of human body shape. Katzmarzyk and Leonard (p. 483) state that “...although climatic factors continue to be significant correlates of world-wide variation in human body size and morphology, differential changes in nutrition among tropical, developing world populations have moderated their influence.” Guatemala Maya, for example, consume only approximately 80% of the total energy needed for healthy growth, and 20.4% are also iodine deficient [The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.Destroy user interface control53]. Iodine deficiency during infancy and childhood results in reduced leg length, especially the distal femur, the tibia and the foot [The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.Destroy user interface control54]. Maya children and adults spend considerable time and energy at heavy labor [The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.Destroy user interface control55], which diverts available energy in the diet away from growth. This nutrition and lifestyle combination is known to reduce total stature and leg length Leitch [The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.Destroy user interface control82] was the first medical researcher to propose that a ratio of LL to total stature could be a good indicator of the early life nutritional history and general health of an individual. Leitch (p. 145) wrote, ‘. . . it would be expected on general principles that children continuously underfed would grow into underdeveloped adults. . .with normal or nearly normal size head, moderately retarded trunk and relatively short legs.’ Reviewing the literature available at the time (pre-1950), Leitch found that improved nutrition during infancy and childhood did result in a greater increase in LL than in total height or weight. 9. Conclusion Prenatal and postnatal undernutrition and disease account for relatively short legs in adults, but still do not explain why they are at greater risk for disease and mortality at earlier ages than the longer-legged adults.[/b] ___________________________________________ ^^^ but with Pygmies a correlation with shorter stature also noted earlier Starting in 1974 Bogin began research on the physical development of Guatemalan Maya children, and their families. Since 1992 he has researched Maya child growth and development after migration to the United States. The purpose of this research has been to document and model the social, economic, and political influences on differences in physical growth and health between Maya children living in Guatemala compared to those in the USA.. _____________________________________________ http://blogs.scientificamerican.com/observations/2012/04/26/why-pygmies-are-short-new-evidence-surprises/ Scientifc American 2012 Pygmy populations, scientists have speculated, may owe their abbreviated stature to natural selection pressures that allowed them to better adapt to dense tropical forests where heat is oppressive and food is scarce. “An outstanding question for many, many years among anthropologists and human geneticists has been what is the genetic basis of the short stature trait in Pygmy populations globally and in Africa in particular, says Sarah Tishkoff, a professor at the University of Pennsylvania, who is a leading expert on African population genetics. “There’s a good reason to think it’s adaptive because in fact in regions of dense tropical forests globally you often have these short-statured Pygmy groups.” Tishkoff and colleagues have found an unexpected surprise in genetic evidence for Pygmy height, which reaches an average of 4 feet 11 inches in Pygmy men in Cameroon. They report in PLOS Genetics today on a set of genes that regulate immune and hormonal processes, and which only secondarily may be linked to height. Pygmies receive an intense assault from pathogens that flourish in the forest and that turn up routinely in their bush-meat diet: expected lifespan is less than 18 years. It may be that genes that protect against microbes may also hinder growth. Diminished stature could be a byproduct of bolstering immune and metabolic defenses and not a direct adaptation to a hunter-gatherer lifestyle. The study was the most incisive to date looking at the genetics of height in Pygmies. Tishkoff says that other studies will undoubtedly turn up genes tied to height in Pygmies and natural selection may still be found to play a direct role in giving rise to short stature. [/QB][/QUOTE]
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