Biocultural Adaptation – Genetic & Nongenetic factors | Anthropology Optional for UPSC PDF Download

Human Bio-cultural Adaptation

• Humans have occupied a wide range of habitats because of their ability to intervene environment- the living and inanimate, for their purposes. This approach is largely based on a notion of adaptability, which regards individuals as being equipped with a set of biological traits that provide means of survival within certain limits. It involves physiological, structural, behavioural or cultural changes aimed at improving the organism’s functional performance in the face of environmental stress. These adjustment can either be temporary or permanent, acquired either through short term or lifetime processes.
• Thereby expressed in terms of phenotype variation of continuous trait, physiological acclimatisation and learned behaviour. There seems to be few situations in which huma population develop genetic adaption to specific environment expressed in terms of phenotypic variation which eventually leads to differences in allele frequency between populations. On the other hand, decades of research affirm that biological plasticity or physiological acclimatisation is species wide adaptive mechanisms which enable individuals to maintain internal constancy or homeostasis. These adaptive strategies represent the continuum and elaboration of adaptive patterns which characterise primate.
• Within the broader content of Human Evolution coping with ecological constrains include culturally coded survival strategies. Culture is a complex entity of technological inventiveness, social institutions, belief systems and idiosyncratic amalgamation with our evolutionary biological and behavioural heritage. It includes technology which range from computers, subsistence pattern ranging from hunting and gathering to agri-business on a global scale, housing type from thatched huts to skyscrapers and clothing from animal skin to high tech synthetic fibres (Jurmain et al., 2006).
• Culture is learned and passed on from one generation to the other. It shapes people’s perception of external environment in particular way that distinguishes one culture from another. It is, however, important to emphasise that culture is not genetically determined and the human predisposition to assimilate culture and function within is influenced by biological factors. Indeed, over the past several million years of human evolution, biology and culture have interacted in such a manner that human are said to be the product of bio-cultural evolution. Thus the aspect of human variation includes the bio-cultural response of population to different kinds of environmentally induced stress i.e high attitude, cold and heat.

Response to Heat

• Human maintain a relatively constant internal body temperature independent of environmental temperature through a complex mechanism of heat gain and heat loss. In hot climate, the fundamental response of human exposed to heat stress is heat dissipation. The process of heat transference between the body and environment includes radiation, conduction, convection and evaporation.
• It has been observed in all human to an almost equal degree, with the average number of sweat glands per individuals (approx 1.6 million) being fairly constant. However, the non-acclimatized individual, on exposure to heat stress exhibits significantly increased perspiration rates (Frisancho, 1993). Further, the effectiveness of the heat removal process depends, on the gradient of heat between the body core and the external environment which involves three factors:
  • The magnitude of heat gradient between the environment and body core.
  • The rate of heat exchange between the interior and skin surface.
  • The rate at which metabolic heat is produced.
• People from the hottest regions (South Asia, Africa, India and Australia) had the largest surface area to body mass ratios. Such a morphological configuration is ideally suited to the more energy-efficient dry heat exchanges, and to a reduced reliance upon evaporative cooling (Taylor, 2006).
• Another adaptive mechanism involves vasodilation, whereby blood capillaries near the skin surface widen to permit increased flow to the skin and hence enhanced peripheral heat conductance.
• Skin color is another adaptive mechanism to the distinct climatic conditions. Melanin pigment produced by melanocytes present beneath the epidermis provides protection from overexposure to ultra violet radiation which can cause genetic mutation in skin cell leading to skin cancer.
• Thereby, natural selection has favored dark skinned individuals in area near the equator where exposure to UV radiations is the most. Biotopes with high densites of UV radiation are also characterised by high temperature. In such biotopes a dark skin color would actually be disadvantageous, as it causes a strong heating of body surface, due to relatively low reflectance. This is explained by differences in numbers and function of the sweat glands among dark skinned individuals.
• The African groups have been able to maintain a lower body and skin temperature as compared to European light skinned people as a consequence of lower suppression of sweat rate than Europeans (Walter, 1971). Thus darkening of skin is of prime biological importance so not only in Negroid, but a functionally effective melanisation is present in South Indians and other ethnic groups also (Weiner, 1964).

Cultural adaptation

• 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 into the 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.

Response to Cold

• Human physiological responses to cold combine factors that increase heat retention with those that enhance heat production (Jurmain et al., 2006). On exposure to cold stress vasoconstriction limits the flow of warm blood from core to the skin thereby lowering the skin temperature. Consequently reduction of temperature gradient between the skin surface and environment reduces the rate of heat loss. The reduction in heat conductance of the blood is also caused by deviation of the blood in the extremities from superficial vein to the deep veins. The countercurrent heat exchange between arteries and vein lower the heat conductance to the periphery.
• In addition, subcutaneous fat layer provides an insulator layer throughout the body. When vasoregulatory mechanisms are not sufficient to counteract heat loss, the organism adjusts by increasing the rate of heat production. Shivering augments the thermeogenesis of the muscle mass and the temperature of muscle is raised to approach that of the core, thus eliminating the temperature gradient heat loss (Frisancho, 1993) shivering also increase the metabolic rate to two three times the basal value which consequently release energy in the form of heat. In general, people exposed to chronic cold maintain higher metabolic rate than those living in warmer climates. The Eskimo living in the Arctic maintain rates between 13-45% higher that observed in non-Inuit.
• Himalayan population of India wear several layers of cloth to combat cold, but extremities remain exposed to cold stress. However, they are characterised by elevated resting metabolic rate and high level of blood flow to the extremity to maintain warm surface temperature during local exposure to cold (Little et al, 1977).
• Body size and proportions are also important in regulating body temperature. In general, within a species, body size increase with the distance from the equator. Two rules that pertain to such relationship between body size, body proportion and climate are:
  • Bergman rule: In mammalian species, body size tends to be greater in population inhabiting colder climates. Increased mass, thereby decreased surface area allows greater heat retention and reduced heat loss eg. Arctic region
  • Allen’s Rule: In colder climates, shorter appendages, with increased mass-to-surface ratios are effective at preventive heat loss. Conversely longer appendages with increased surface area relative to mass permit heat loss eg. Sub Saharan Africans.

Cultural adaptation

• 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.
• Coribou fur of 1½ and 3 inches thickness provide insulation equivalent to 7 to 12 clo units (Scholander et al., 1950) 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 ownship 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.

Response to High Altitude

• A high attitude environment exerts multiple stresses on human which include hypoxia, more intense solar radiation, cold, low humidity, wind, a reduced nutritional base and rough terrain. Of these, hypoxia exerts greater degree of stress on physiological functions and is not easily modified by cultural behavioural practices or responses. Hypoxia results from a decrease in partial pressure of  oxygen in atmosphere proportionally to increase in the attitude which consequently leads to reduction in O₂ Heamoglobin saturation. It interferes with the oxygen acquisition at the cardiopulmonary level and utilisation by the cells.
• Hypoxia induced anorexia and dehydration due to increased ventilation and low humidity at high attitude leading to weight loss. The multifaceted effect of hypoxia also manifests through increased rates of infant mortality, miscarriage and prematurity among people residing at higher elevation. Decreased foetal growth due to impaired maternal foetal oxygen transportation also results into birth of low birth weight babies.
• Thus, acclimatisation to high attitude hypoxia is a complex phenomenon that develops through the modification and synchronized interdependence of the respiratory, circulatory and cardio vascular system to improve oxygen delivery and utilisation. On exposure to high attitude low landers, acquire short term modifications or partial acclimatisation in response to hypoxia which include increase in respiration rate, heart rate, and production of RBC which contain oxygen-transporting protein heamoglobin while high attitude dwellers adapt to hypoxia during their lifetime, as they mature.
• During growth and development environmental factors constantly condition and modify the expression of inherited potentials. The environmental influences felt by the organisms depend on the type of stress imposed and especially on the age at which the individual is subjected to the stress. The respective contribution of genetic and environmental factors varies with the development stage of the organism, in general (Frisancho, 1993).
• The earlier the age or the longer the duration of stay at high altitude, the greater the environmental influence on body dimensions and respiratory functions. For instance, the altitude natives Anedean Indians have larger chests and greater lung capacity as well as more surface areas in the capillaries of lungs which facilitate the transfer of oxygen to the blood. Consistent with a presumed environmental effect, the children of high attitude Peruvians who grow up in low lands don’t develop larger chests. Peruvian who were born at sea level but grew at up at high attitude developed the same amount of being capacity as people who spent their entire lives at high attitudes (Ember & Ember, 2008).
• Thereby larger chests among Andeans which was considered to be a genetic adaptation, infact, presents acclimatisation which develops early in childhood and persists for the lifetime of an individual. The Spitians who inhabit high altitudes in the North West Himalayas showed large chest size in relation to stature indicating developmental adaptation to low oxygen pressure of high altitude (Singh et al. 1986). The larger chest circumference of the Bods of Ladakh as compared to lowland Indians also suggests a structural response to the greater lung function capacity and adaptation to high altitude hypoxia (Kapoor & Kapoor, 2005; Bhasin et al. 2008;).
• Rajis, a hunter-gatherer tribal population of Uttaranchal showed lower chest circumferences comparable to the mid-altitude population but lung functions comparable to those of other high-altitude populations. This leads to the conclusion that indigenous high-altitude populations may possess different genetic potential for thorax growth compared to low-altitude populations, possible related to ethnic differences in the rate of growth of thorax related to stature at high (Kapoor et al., 2009)

Cultural adaptation

• Acclimatisation to high altitude also concerns with the utilisation of glucose, a critical O₂ efficient source of energy for brain. There is an apparent dependency on blood glucose under both resting and exercise conditions and increases with the length of exposure to high altitude.

Conclusion

Humans have developed various bio-cultural adaptations to cope with different environmental stresses such as heat, cold, and high altitude. Physiological and structural changes, as well as learned behaviors, are employed to maintain homeostasis and ensure survival. These adaptive mechanisms are influenced by both genetic and environmental factors, with culture playing a significant role in shaping human responses to environmental stress. Cultural adaptations include technological inventions, housing, and clothing that help maintain favorable microclimates and protect against harsh conditions. Overall, the study of human bio-cultural adaptation provides valuable insights into the complex interplay between biology, culture, and the environment in shaping human evolution and survival strategies.