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Humans have successfully adapted to extremes of environment, including extreme cold. As a species, we have survived Ice Ages which brought the intensely cold environment which is normal to our polar regions across much of the planet. To understand the wide variety of adaptations which have proven successful, we explored existing literature which analyse data from archaeological, historical, and anecdotal sources, as well as current populations. We define 'extreme cold,' in terms of environment, by examining monthly mean temperature charts provided online by the U.S. Navy (Guest, 2000). These data show that monthly mean temperatures at sub-polar locations, both north and south, range from -30Â° C (-22Â° F) in January to +5Â° C (+41Â° F) in July, with daily variations from -40Â° C (-40Â° F) to +30Â° C (+86Â° F) yielding average annual temperature of ~ -14Â°C (7Â°F). Ample evidence exists to support conclusions that humans have made structural, functional, physiological, and behavioral adaptations in order to survive existence in extremely cold environments. Structural adaptations can be seen in elongated and narrowed nasal passages, foreshortened limbs, broad pelves, and a relatively short, stocky bodies. (list references) Functional adaptations include: increased basal metabolic rate, high protein/high fat/low carbohydrate nutritional requirements, and some evidence of variations in blood chemistry. (list references) Physiological adaptations are observed in mapping of active sweat glands, body hair patterns, and percentage of adipose tissue. (list references) Additionally behavioral adaptations can be observed in agriculture, methods of harvesting flora and fauna, awareness of fickle environmental factors, and clothing. (list references) For example, Some populations demonstrate acute awareness of weather patterns, modifying their behaviors to minimize exposure to dangerous conditions while taking full advantage of more temperate periods. Typically hunter-foragers, agriculture is limited to what can be cultivated in the short growing season. Unique methods for harvesting sea mammals, land mammals, fish and birds have developed according to available materials and ingenuity. (list references)
"Fueguians and the Eskimos are the human groups with the narrowest and highest nasal apertures, displaying a combination of large nasal height and low nasal breadth values, while groups from equatorial areas have low, wide nasal passages" (Herná, et al. 1997). Both groups lived and/or live in the sub-polar regions (one nearer the southern pole, one nearer the northern). Fueguians inhabited Tierra del Fuego, the southernmost tip of South American after the ice sheets receded, ~ 10,000 BP to 12,000 BP. Unlike the sub-Arctic environment, which is cold and dry, the climate of Tierra del Fuego is extremely cold, rainy, foggy, and windy. Average temperatures are in line with our definition of 'extreme cold,' but in addition the area receives ~3000 mm (118 in) of rain each year and strong, persistent winds that blow off the glaciers, inducing a significant windchill affect. Herná, et al. (1997) took craniometric measurements of 180 skulls from three distinct tribal groups of the area and analyzed them in relation to Howells 28 craniometric series. When all the meaurements were plotted on a climate map, there is a strong correlation between increased nasal height combined with narrow breadth and extremely low temperatures. Researchers postulate that high, narrow nasal openings allow frigid air to be warmed by the mucous membranes lining the nasal cavity to prevent damage to delicate lung tissue, and enhance "the recovery of heat and moisture from expired air." (Herná, et al. 1997)
"Body proportions of humans [and other endothermic (i.e., ''warm-blooded'') species] have long been known to show significant correlations with climatic variables and their proxies. Specifically, two empirically derived ecogeographical rules, those of Bergmann (1847) and Allen (1877), state that within a widespread endothermic species, those in colder regions will tend to weigh more (Bergmann's rule) and be characterized by shorter appendages (Allen's rule) than their conspecifics in warmer climes." (Holliday and Hilton, 2010 and references therein). They also put forward that "colder-climate groups being characterized by broader pelves," and reference C.B Ruff's work from the early 1990s. Holliday and Hilton (2010) examine skeletal data from the Point Hope Inuit of North America. A total of 173 individuals, 127 from the Tigara period (13th to 17th century AD) and 46 from the Ipiutak period (~100 BC to 500 AD) were measured and analyzed relative to samples from to Europe, North Africa, Sub-Saharan Africa, and other Native North Americans. Based on results from previous studies referenced, effort was concentrated on measurements which have been determined to vary with climate, "specifically limb bones from the four major limb segments, femoral head diameter, skeletal trunk height (the summed dorsal body heights of T1-L5 plus sacral ventral length), and bi-iliac breadth." (Holliday and Hilton, 2010) From the basic measurements, the authors computed various ratios which are identified as indices for comparison. Femoral head diameter: femoral length = relative femoral head size, radius length:humerus length = brachial, tibial length:femoral length = crural, and ratios from each limb bone related to the trunk height are used to highlight patterns relevant to the study. In addition, pelvic breadth is compared to an assumed trunk height determined by adding leg bone lengths to skeletal trunk height in order to ascertain yet another useful measurement ( relative bi-iliac breadth index). Results show that African samples provide the lowest indices while circumpolar populations show the highest, with European numbers in the middle. Neither of the groups measured specifically for this study (nor the other Native North American sample) is significantly different from the other, but marked variations exist between these groups and both of the African groups. Interestingly, results do not support the authors' expectation that the Inuit and Europeans would also show a discernible variation in most basic parameters. However, the bi-iliac relative breadth index did separate these two groups distinctly. As a counter-point, it is noted that there are other factors which can affect overall stature, such as malnutrition. In a harsh environment, maintaining sufficient nutritional intake is likely compromised, and so the shorter body may be simply an adapation to the extremely cold environment.
"Extreme cold favours short, round persons with short arms and legs, flat faces with fat pads over the sinuses, narrow noses, and a heavier-than-average layer of body fat." (Encyclopædia Britannica, 2011) Popular rhetoric holds that a layer of body fat helps keep humans, and other mammals, warm. In his 2007 article "Human cold adaptation: An unfinished agenda." ( American Journal of Human Biology) Steegmann does not disagree; he does say, "Fat insulates better than muscle per unit of thickness. However, in a fit person, muscle layers are usually much thicker than subcutaneous fat and consequently have higher absolute insulative value." Studies in the 1950s and 1960s (referenced in Elsner (1963): LeBlanc, 1954; Baker and Daniels, 1956; Daniels, et al, 1961) demonstrated that Caucasians with a thicker layer of body fat, as measured by skinfold, maintained core temperature, skin temperature, and metabolic rate more reliably when exposed to 15Â° C (59Â° F) for two hours. However, in a similar study (Elsner, 1963) compared the skinfold thickness of eight hunter-gatherer groups (aborigines of central and northern Australia, Inuit of Canada, Eskimos, Alacaluf Indians of southern Chile, Lapps, Peruvian Indians, and Kalahari bushmen), cold-acclimatized Norwegian students, with urban Caucasians as a control. Skinfold thickness was measured at ten locations: abdomen, back(subscapular), calf, cheek, chin, iliac crest, knee, pectoral, upper arm,and side. The urban Caucasian control group had higher values across the board, except for the cheek measurement. Of particular interest, Canadian Inuit, and Eskimos had amongst the lowest values; not what was expected from populations that acquire 70-75% of their caloric intake (see above) from animal fat. Additionally he measured the rectal temperature, metabolic rate, and skin temperature of his subjects during an eight-hour sleep period with ambient room temperature of 0Â° - 5Â° C (32Â° - 41Â° F) during which time they had only one thin blanket to wrap up in. Elsner reports that there was poor correlation between skinfold thickness and the measurements of interest during the overnight study. In support of these findings, from another study, Steegman (2007) reports results which demonstrate that Inuit "traditionally had high muscle mass and high work capacity, but low body fat." Aside from the subjective observation that the "primitive" groups had "better sleep" than the control group, three sets of reactions emerged from Elsner's study: 1) Canadian Inuit, Eskimos, and Alacaluf Indians, and cold-acclimatized Norwegian students demonstrated high metabolic rates (measurement technique not defined) and warm extremities; 2) Kalahari bushmen and aborigines from central Australia had stable or falling metabolic rate and cooler skin; and 3) Peruvian Indians and Lapps had low rectal temperatures and higher extremity temperatures. So, while a thicker layer of body fat does not seem to be a human adaptation for survival in extremely cold environments, increased metabolic rate and some protective mechanism to keep extremities warm do appear likely. (references and info on other physiological adaptations (muscle mass/body hair placement/sweat gland activity- misplaced articles on computer)
"...An inverse relationship between BMR and mean annual temperature has been documented, which holds true even when controlled for differences in body size." (Snodgrass, et all 2005) In fact, Snodgrass, et al (2005) conducted extensive research among the Yakut population in Siberia which corroborates that increased basal metabolic rate is an important human adapation to an extremely cold environment. With a thorough and well-documented scientific process, participants underwent measurements of core temperature, oxygen consumption, carbon dioxide production, and heart rate in a thermoneutral (23Â° - 27Â° C) environment after a 12-hour fast. Results for basal metabolic rate (BMR) were predicted based on three standards drawn from a European population: fat-free mass (FFM), surface area (SA), and body mass. In all three cases, for males and females, the Yakut BMR significantly higher than predicted values. The BMR of Yakut men and women were demonstrably elevated over their more southern-dwelling, European counterparts. Another metabolic adaptation might be seen in the increased incidence of Type 1 diabetes mellitus among northern Europeans, particularly those of Scandinavia and Sardinia. Moalem, et al (2004) say "Recent animal research has uncovered the importance of the generation of elevated levels of glucose, glycerol and other sugar derivatives as a physiological means for cold adaptation. High concentrations of these substances depress the freezing point of body fluids and prevent the formation of ice crystals in cells through supercooling, thus acting as a cryoprotectant or antifreeze for vital organs as well as in their muscle tissue." Citing the example of cystic fibrosis conferring immunity to typhoid (salmonella typhi), the authors suggest that elevated blood glucose levels, such as are seen when the body does not produce insulin, may be the result of genetic mutation which gave an evolutionary advantage to inhabitants of cold climates about 14,000 years ago when world-wide temperatures dropped dramatically. Life expectancies then were short, so genetic adaptations that made sense would have favored changes in the short term. Now that our life expectancies have increased to 70+ years, we can observe that such changes might have been beneficial then, but now they are causing dangerous health issues within the aging population. Moalem et all also discuss the development of brown adipose tissue (BAT) which is a particular type of fat tissue thought to create heat (thermogenesis) using gulcose as a fuel under cold-stressed circumstances. Traditional dietary intake of these populations of cold-dwellers depends completely on what is available at any given time. In 2004 Patricia Cochran, a native Inuit Alaskan, wrote an article for Discovermagizine.com. "Our meat was seal and walrus, marine mammals that live in cold water and have lots of fat. We used seal oil for our cooking and as a dipping sauce for food. We had moose, caribou, and reindeer. We hunted ducks, geese, and little land birds like quail, called ptarmigan. We caught crab and lots of fish-salmon, whitefish, tomcod, pike, and char. Our fish were cooked, dried, smoked, or frozen. We ate frozen raw whitefish, sliced thin. The elders liked stinkfish, fish buried in seal bags or cans in the tundra and left to ferment. And fermented seal flipper, they liked that too." She reports that in the short summers the family foraged for roots, greens, and berries, typical summer activities for people of her village. "What the diet of the Far North illustrates," says Harold Draper, a biochemist and expert in Eskimo nutrition, "is that there are no essential foods-only essential nutrients. And humans can get those nutrients from diverse and eye-opening sources." Inhabitants of extremely cold climates do not live to eat, they eat to live. Inuit bodies are efficient at extracting nutrients from available sources. Fat-soluble vitamins A and D are metabolically mined from cold-water fish and mammal fats and livers. Vitamin C, a vital component for healthy connective tissue, is found in raw animal organs, raw kelp, and even muktuk, which is as rich in Vitamin C as orange juice, gram for gram. Not surprising, then, that the traditional Inuit diet comprised 90% of its caloric intake from meat and fish, 50-70% of its calories specifically from wild animal fat - fat is the source of not only calories but also necessary nutrients. Their dietary efficiency may or may not be a metabolic adaptation to generations in the extreme cold, but it is a remarkable thing, nonetheless.
Perhaps this subsistence diet, based wholly on what food is available from hunting, fishing and forage-harvesting, is more of a cultural adaptation to the climate. While structural and physiological adaptations to environment take eons to manifest, some cultural and social adaptations may be apparent on a far shorter time scale. Steegmann (2007, and references therein) speaks about Richard K. Nelson's comparison of Kutchin natives of east-central Alaska to Eskimos, explaining Nelson's observation that Kutchin hunters keep moving if they lose their way, afraid if they stop they will sleep and freeze. Eskimo rest as needed and only move to stay warm. He also noted that Eskimo had a complex understanding of weather prediction and were better equipped to plan accordingly and keep themselves safe. "In both cases, Eskimos seem to practice higher survival skills and both behaviors are strongly directed by cultural traditions." Two very different responses to the same stimuli in similar environments, with potentially diametrically opposed results: survival and death. Another surprising and non-intuitive variation in responses to the extreme cold of sub-polar life can be found in the clothing styles of arctic and some sub-arctic populations. According to Herná, et al. (1997) arctic inhabitants, such as the Inuit, wear clothing designed to protect them from the harsh cold, whereas the three Fuegian tribes they study, who lived at the southern tip of South America, are anecdotally described as "almost naked throughout their lives." The Fuegian tribes are extinct, so no opportunities to explore their cultural adaptations to their extreme environment.