Behavioural Adjustments
Humans are biologically tropical, better equipped to survive in hot rather than cold climate. They do not possess thick layers of subcutaneous fat or thick fur which otherwise provide insulation to body against cold. Thus, a substantial portion of cold adaptation in this hostile climate is behavioural. Behavioural adjustments are cultural responses of humans to cope with environmental stresses. These adjustments are not inherited from one generation to the other. Hence, behavioural adjustment must be made by each generation as newborn infants learn their culture. It includes seeking shelter, using protective clothing, improving housing and other technologies.
Housing
A clear example of how culture permits people to survive in stressful habitats is housing. House form is a reflection of many variables, including the size of the household unit and availability of raw materials. It also reflects socio-cultural features such as religious beliefs, family and clan structure, social organisation, way of gaining a livelihood and social relations between individuals.
Environment plays a major role in the development of house type; its significance lies in areas under environmental stress, e.g. Igloo of the Eskimo. The igloo consists of a dome-shaped structure connected to the outside by a tunnel. It is made up of snow, which is an excellent insulator as it traps the air within itself. Heat is produced by a small seal-oil lamp within the structure. This melts the snow slightly during the day and refreezes at night, forming an icy reflective layer on the inner side. The reflective layers accompanied with the dome structure serve to reflect the heat throughout the igloo. Relatively little heat is lost to the outside since the dome shape minimizes the surface area from which heat can radiate. A long tunnel way helps to warm the air gradually as one enters the structure, and also block the entry of wind into the habitation area. Habitation structure is one aspect of a human technology. There are other aspects of technology also which enable human to survive in stressful environments including, for short periods of time, outer space.
Social Response
In addition behavioural adaptation humans adjust their social organisation to their environments. For instance, Eskimos, living in extremely harsh environments use a number of strategies to reduce environmental stress. Anthropologist Knud Rasmussen during a trip to King William Island discovered that in a sample of eighteen marriages, 38 out of 96 female infants born were put to death. This strategy of female infanticide is practiced by the Netsilik Eskimos to increase the ratio of males to females. Such numerical balance between the sexes reduces stress of male hunters to support unproductive members of society. Also, in the harsh northern environments females are considered to have less survivability than males. People in these habitats also practice suicide, invalidicide, and senilicide in crisis situations. Infanticide is usually an extreme response to extreme conditions, although it has been practiced in a wide variety of human societies. All human societies in some way adjust economic, political, social, religious, and other aspects of their social systems to the environmental conditions. This socio-cultural flexibility, in part, allows humans to exist in so many habitats.
Cultural adaptation to heat
It pertains to the creation and maintenance of favorable environmental conditions near the individual – microclimate, different from those in the general area. The ideal microclimate involves lowered skin temperature, a vapour pressure gradient favoring evaporative heat loss, and protection from conductive, convective and radiation heat gain. It is within the extrasomatic zone that behavioural and social adaptations play a major role by maintaining a favorable microclimate within a larger and more stressful macroenvironment. (Hanna, 1983).
Material Culture as habitations and clothing establish a favorable microclimate while behavioural adaptation centre’s largely upon avoidance. Houses are constructed of high heat capacity materials such as adobe and stone, to delay entry of heat. These materials absorb large amount of heat before passing it intothe interior and the stored heat is lost at night by radiation and convection. The net effect is to dampen temperature fluctuation so that interior temperature remains moderate. Pueblo Indians, Middle Eastern communities construct their house several meters beneath the surfaces as the mean temperature of subsoil is more comfortable that the surface with its extreme variation. In habitation above the ground, compact geometry minimizing surface area to internal volume reduces solar heat gain as well as convention heat gain from desert winds.
Clothing, another aspect of material culture reduces abrasions, prevents sunburn and reduces solar heat gain. This in turn reduces level of perspiration required to maintain equilibrium. It has been proposed that well-acclimatized individual wearing clothes perspire 30% less than unclothed men at rest which reduces the heat load of about 165 kcal/hr. (Henschel and Hanson, 1959) .
Chaamba Arabs, tribal population of Sahara Desert wear clothing that minimises conductive and radiant heat gains from the environment. The insulative effects of trapped air reduce heat transmission to the skin surface. However, clothing is less advantageous at work than at rest as it hinders the loss of internally generated heat and loose fitting, baggy clothing is desirable. Such cases, favors ventilation and evaporates from the skin surface. Furthermore, a light-colored external garment may reflect radiation reducing heat gain.
Cultural adaptation to cold :
The diurnal-nocturnal variation in the temperature exposes the Aborigines of Australia to heat stress during day and moderate cold stress during night. As they wore no clothing and did not built shelters, the heat against the cold stress is provided by sleeping fires. They also experience continuous vasoconstriction throughout the night which prevents them from excessive internal heat loss with no threat of frostbite. The Bushman of Kalahari Desert, like the Australian Aborigines are exposed to moderate chronic cold stress during night. They have been able to create a microclimate around their bodies that is close to the thermoneutral temperature of 25°C through efficient use of fires and skin cloaks during cold nights (Frisancho, 1993). They sleep in a group of three or four in families or in single sex groups. The heat made up of grass and boughs are placed in a half-circle as wind breakers.
Eskimos occupy the northwestern coast of North America and across the Bering Strait into Asia. They have well insulated housing known as ‘Igloo’. Their wall made of whole rib rafters are covered with a double layer of seal skin attired with moss. They place the source of heat usually an oil, blubber or coal lamp at a lower level than the main floor; where by cold air is warmed before it reaches the area where people live. The housing structure permits trapping of air which in turn further provides insulation. Such an efficient heat exchange system maintains between 10ºC to 21ºC for coastal Eskimos despite subzero environmental temperature. Their clothing is made of caribou which provides higher insulation as compared to seal skin. Although Eskimo wear snowshoes and short skin mittens at times, during their daily activities such as fishing, their hands and feets are continuously subject to cold stress. They experience intermittent periods of vasoconstriction and vasodilation which prevent frost bite in below freezing temperatures. At the same time, because vasodilation is intermittent, energy loss is restricted, with more heat retained at body’s core. The high peripheral temperatures of extremities and high tolerance to cold of Eskimos and highland Quenchas appear to reflect the influence of developmental acclimatisation. Traditionally they have the highest animal protein and fat diet than any other human population. Such a diet, necessitated by the available resources base, served to maintain the high metabolic rates required by exposures to chronic cold.
The highland Quenchua population from the Peruvian Andes and other mountain areas of South America are exposed to a variety of stresses including hypoxia cold, low humidity and high levels of solar radiations. Thus, interpretation of cold adaptation of the highland population requires a synergic interpretation of all these stresses. The success of the Quenchua population in preventing severe body cold stress reflects the effectiveness of their technological adaptations, which includes housing, bedding and clothing. The housing of the highland natives differs with the variation in altitude and subsistence pattern. Population living below 4000m has mixed economy owing to individual or community ownership of land. They have permanent houses built of Abode which maintain the indoor temperature more than 10ºC above the outdoor temperature. On the other hand, housing at elevation above 4300m are temporary is a consequence of pastoral economy requiring high mobility. However, these houses constructed of piled stones and roofed with straw have inadequate insulative effectiveness with the average indoor-outdoor differential temperature of 3.7ºC. They sleep within the woolen sleeping bags providing adequate protection against cold stress. Clothing results in 4ºC increase in temperature of the skin under clothing.
Cultural adaptation to high altitude
Cultural adaption to high altitude is best presented by the examples of Sherpas and the Aymaras. The Sherpas are the tribe of Tibet occupying the high valleys around the base of Mount Everest, Nepal. The Aymaras are the residents of Andean mountains of Bolivia. The Sherpas construct houses as a cluster in a group at the center of village’s agricultural land. House has two stories made of stone. The roofs are flat and made up of wood, weighed down by heavy stones. Both sexes wear a long inner shirt over a pant-like garment made up of wool. Both males and females wear high, woolen boots with hide soles. The Aymara of Ethiopia construct house as oblong building using adobe. At the lakes houses are build using reeds (tall, slender leaved plant). The roofs are thatched with reeds and grasses. In the altiplano (high altitude), men wear cotton trousers and woolen caps with ear flaps and also wear ponchos. Women wear home spun skirts and sweaters. Both sexes use sandals or shoes.
Nutritional Adaptations
Nutrition plays an important role in adaptation. Metabolic adaptations to heat, cold and high altitude are also associated with nutritional requirements. Inadequate nutrition may impair metabolic response (Murthy and Singh, 2003).
Heat: Adequate drinking water prevents dehydration, heat illness and reduced performance at work (Murthy and Singh, 2003). Energy requirement increases in hot climates due to additional work of ventilation and increased sweat gland activity. In hot climate, minimal deficiency of vitamin B occurs due to profuse sweating and inadequate dietary intake. Additionally, the requirement of salt also increases in hot climate due to sweat conditions. Accentuation of sodiumpotassium exchange system increases the potassium loss (Malhotra et al., 1981; Pichan et ah, 1988).
Cold: Energy requirements increases in cold regions due to hobbling effect of clothing weight and associated with efforts of locomotion (Gray et al., 1951). In cold climate, the level of appetite increases which is the result of increased activity levels and energy expenditure due to thermogenesis, social isolation and modification in the diet. Diet of Arctic and subarctic regions and expedition members of various countries to Antarctica adapt to high fat diet to cope cold climate.
High altitude: The effects of high altitudes include decrease in significant amount of body mass, fat mass and fat free mass due to hypoxia related conditions such as aneroxia (low weight due to limited energy intake), hypophagia (reduction in food intake), reduced calorie consumption and increased metabolic rate. High intake of carbohydrate and dietary protein is considered to be advantageous to adapt in high altitude environment.