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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] http://anthropology.ua.edu/blogs/emmakoenig/page/2/ "So, large animals should live in cold climates because there is less SA to lose heat from and smaller animals should live in warm climates because they can increase heat dispersion (Bergmann’s). Furthermore, species living in tropical climates should have a [b]linear body plan[/b] with most mass in the limbs (long legs) and less in the trunk (~Short torso) to dissipate heat, whereas, Arctic species should have large trunks (~long torso) and short limbs to conserve heat (Allan’s)." In 1953 D.F. Roberts did a study to test these two rules. He looked at 116 males from around the world and found that there was a negative correlation between body mass and average temperature based on Relative Sitting Height (RSH=sitting height/stature) people in cold climates as compared to warm climates had short legs but larger RSH. In 1998 the authors did the same type of study using a sample of 223 males and 198 females from around the world and compared it to Robert’ 116 males. The same results as Roberts’ were found but the negative regression slopes were much shallower. In addition the authors calculated the Body Mass Index (BMI=weight (kg)/height (m^2)) and body surface area (using the Bailey and Briars equation pg. 158). RESULTS: - When compared to Roberts’ sample, males were taller and heavier with lower SA:mass ratio. This says overweight and obesity (BMI ≥ 25kg/m^2) has risen from 3.4% to 12.2%. - Roberts had no female data but as expected compared to males, females are shorter and lighter but have higher SA/mass ratio with a 15.6% prevalence of overweight and obesity. - For all groups (Roberts, males and females) as body weight decreases, mean temperature increases. - For all groups as BMI decreases, mean temperature increases. - For all groups as SA/mass increases so does mean temperature. - For males and females of the current sample RSH decreases as temperature increases Overall, the results show that body mass has increased disproportionately in the tropics than the rest of the world. Body weight in the current sample is 50% larger in populations of warm climates as compared to cold climates and BMIs are twice as large as the cold climate counterparts. Again, even though there has been a relative trend for increasing body mass from 1953-1998 the tropics show disproportionately larger results. PROBLEMS WITH BMI The BMI is the most widely used standard in assessing nutritional status around the world for adults. The problem with using BMI is that it does not take into account body proportions and morphology. So someone very tall may be considered undernourished according to BMI when actually healthy because the ratio of height to weight causes the disparity. The example given by the authors compares Australian Aborigines and Inuit. “…Australian Aborigines studied before the 1970s had very low BMIs, suggestive of chronic undernutrition, yet had skinfold thicknesses that indicated adequate nutritional status. Conversely, early work among Inuit men and women has shown that despite having BMIs that were at or above the threshold for “overweight,” they were relatively lean, as reflected in both skinfold measures and estimates of body fatness from hydrostatic weighing.” (164) By correlating climate, BMI, RSH and skinfolds it was found that morphological differences directly related to climate significantly influenced BMI results. Individuals in cold climates are leaner than BMI expectancies while individuals in warm climates are fatter than BMI expectancies. Take Home= body proportions need to be taken into account when assessing BMI for nutritional status and additional anthropometric measures should be used as well. [/QB][/QUOTE]
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