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Population Affinities of the Jebel Sahaba Skeletal Sample (Holliday 2013)
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[QUOTE]Originally posted by Troll Patrol: [QB] On what page can this be found? [i]"limb proprtion can change relatively quickly, alteration of body width occurs much more slowly"[/i] - Principles of Human Evolution 2013 By Robert Andrew Foley, Roger Lewin And what is "relatively"? Relatively in the sense of human evolution, 15,000 to 18,000 years is indeed quickly. [QUOTE]Migration within a larger time framework took place ca. 15,000–18,000 BP, when the first Asian populations crossed the Bering Strait, ultimately founding the modern Amerindian population. Despite having as much as 18,000 years of selection in environments as diverse as those found in the Old World, body mass and proportion clines in the Americas are less steep than those in the Old World (Newman, 1953; Roberts, 1978). [b]In fact, as Hulse (1960) pointed out, Amerindians, even in the tropics, tend to possess some ‘‘arctic’’ adaptations. Thus he concluded that it must take more than 15,000 years for modern humans to fully adapt to a new environment (see also Trinkaus, 1992). This suggests that body proportions tend not to be very plastic under natural conditions, and that selective rates on body shape are such that evolution in these features is long-term."[/b] [/QUOTE]- Holliday T. (1997). Body proportions in Late Pleistocene Europe and modern human origins. Jrnl Hum Evo. 32:423-447 [IMG]http://books.google.nl/books?id=dDWsTli1k54C&hl=nl&pg=PT199&img=1&pgis=1&dq=limb+proprtion&sig=ACfU3U3jnItVy9hNhI7NVZtCfv8dw4y5Fw&edge=0[/IMG] [IMG]http://books.google.nl/books?id=dDWsTli1k54C&hl=nl&pg=PT204&img=1&pgis=1&dq=limb+proprtion&sig=ACfU3U3_9g5MlhNDuhwdzP2sDsinDwaw7A&edge=0[/IMG] [QUOTE]The link between anatomy and clim- ate relates to thermoregulation, or the balance between heat produced and the ability to dissipate it. This rela- tionship translates to the ratio of the surface area to the volume of the cylinder, or body mass. In hot climates, a high ratio – that is, a large surface area relative to body mass – facilitates heat loss. In cold climates, a low ratio – that is, a small surface area relative to body mass – allows heat retention. Simple geometry shows that the ratio of surface area to body mass is high when the cylinder is narrow, and low when it is wide. This finding forms the basis of Bergmann’s rule. A strong prediction flows from this analysis: people living at low latitudes will have narrow bodies and a linear stature, while those at high latitudes will have wide bodies and a relatively bulky stature. When Ruff surveyed 71 populations around the globe, he found that the prediction was sustained very well (Fig. 6.14). He also discovered that Allen’s rule applies convincingly, with tropical people having longer, thinner limbs, which maximizes heat loss, while people at high latitudes have shorter limbs. This difference in limb proportions enhances the linear look of tropical people and the stocky appearance of high-latitude populations. A comparison of the tall Nilotic people of Africa with the relatively stocky Eskimos in the northernmost latitudes of North America illustrates this difference very clearly. Body width represents the key variable, even though tropical people also tend to be linear. A further step of simple geometry shows that linear- ity is not a necessary feature of low-latitude populations. The ratio of the surface area to body mass in a cylindrical model of a certain width is not altered by changing its length, as Fig. 6.13 above shows. [b]Peoples who live in similar climatic zones will have the same body width, no matter how tall or short they are, because they have the same surface area to body mass ratios (Fig. 6.15).[/b] [/QUOTE]Page 146 [QUOTE] figure 6.18 Body proportions in early modern humans and Neanderthals: Limb proportions of modern humans in relation to temperature are shown in the graph. The limb proportions of early modern humans and Neanderthals are indicated by arrows, and suggest that the former were tropical in origin, while the latter were cold-adapted. (Courtesy of C. Stringer.) [/QUOTE]page 150 - Principles of Human Evolution 2013 By Robert Andrew Foley, Roger Lewin [IMG]http://img845.imageshack.us/img845/6536/tropicalroundup2big.jpg[/IMG] [/QB][/QUOTE]
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