Some ten to twenty-five million people (that is less than 1% of theearth’s population) currently make ithigh altitude zones theirhome(Moran,143).” The adjustment high altitude populations must make are firstlyphysical and secondly cultural. Although most people adapt culturally to theirsurroundings, in a high altitude environment these cultural changes alone aren’tenough. Many physical adaptations that reflect “the genetic plasticity common toall of mankind(Molinar,219)” have to be made to survive and even more than thatthrive in this type of environment.
In this paper I will describe the high altitude stresses. Along withadaptations made by the populations living in them. The two high altitudepopulations which I will examine in this paper are the Tibetan people of theAsian Himalayas and the Quechua of the South American Andes.
The Quechua are an Indian people who inhabit the highlands of Peru andBolivia. They speak Quechua, which is a branch of the Andean-Equitorial stock. They show many remnants of Inca heritage by their houses, music, and religionwhich has pagan rites under the Roman-Catholic surface. Their villages consistof kin groups . Their marriage partners are taken from within each village.
Agriculture is the dominant subsistence pattern in the centralAndean region but the Nunoa region where the Quechua reside can only support afew frost-resistant crops. Which include bitter potato, sweet potato, and a fewgrain crops of quinoa and canihua. The rest of the fruits and vegetables of theQuechua come from the eastern mountains on it’s way to the markets. The mostimportant subsistence pattern for the Quechua is stock raising. Which is limitedto the few animals that do well in the high altitudes. Their stock includealpacas,llamas and sheep.
In the Himalayas only “5% of the geographical area(Baker,36)” can beused for agriculture. The main crops are barley, wheat and buckwheat. The cropsare grown between 3,500 and 4,300 meters. These few crops are threatened bydrought, hail, frost, snow and erosion. The Himalayas also have extensivepasture areas which are used by the nomadic and sedentary peoples. The higherregions have pastures where yak, sheep, and goats are the main animals used.
In the high altitude there are many environmental stresses that thepeople must endure. They include hypoxia, intense ultraviolet radiation, cold,aridity, and a limited nutritional base. The people adapt to these stresses inmany ways.
Hypoxia, or low oxygen pressure, is the most prominent stress whichpopulations living at high altitudes must deal with. “Hypoxia results whenevereither physiological,pathological, or environmental conditions cannot deliveradequate supply of oxygen to the tissues. Since air is compressible, air at highaltitudes is less concentrated and under less pressure. At 4500 meters thepartial pressure of oxygen is decreased by as much as 40%, in comparison topressure at sea level. This reduces the amount of oxygen finally available tothe tissue(Moran,147-148).” The adaptations to hypoxia are all geared towardsincreasing the oxygen to the tissues.
One adaptation to hypoxia is an increase of red blood cells incirculation. A person living in high altitude conditions is likely to have “30%more red blood cells(Molinar,218)” than a person living at sea level. “Thisgreater number of red blood cells increases the hemoglobin concentration, whichin turn increases the oxygen -carrying capacity per unit volume ofblood(Molinar,219).”
This then increases the oxygen sent to the tissues. Respiration and cardiac output are also increased. There is an increase in thecapillary network to aid diffusion of oxygen to the tissues. There have alsobeen cellular changes that increase the resistance to the tissues to low oxygen.
Many other effects are felt from hypoxia. Growth and development are oneof the many areas affected. Kruger and Arias-Stella compared two populations at4,570 meters and at 200 meters and found the mean placental weight of the highpopulation to be 561 grams as compared to the low-land population weight to be500 grams. Placenta volumes did not differ showing that the placenta at the highaltitude was denser. The denser placenta offers the fetus more protection andgreater oxygen.
The birth weights at high altitudes are uniformly lower thanthat of low altitude.This is probably due to hypoxia but the nutritionalstatus of the mother’s must also be taken into account. A study by FrisanchoVelasquez and Sanchez demonstrated that subjects with short stature attained agreater maximal aerobic capacity than their counterparts of a larger body sizewhen tested under identical conditions. It is known that ” birth weight is saidto be correlated with maternal size particularly stature(Baker,95)” thereforesmall birt h weight is an effect of the adaptation of body size to deal withhypoxia.
Growth and development in high altitude populations is considerablyslower than low-land growth.This may be due to the growth of their large chestsand the extra production of the red blood cells from the bone marrow. This extralarge chest growth increases the lung capacity to take in more oxygen. Althoughin the Himalayas this increased chest size is not a factor. Baker shows growth in stature occurs until the twenty second year.
Sexual dimorphism isn’t defined until the 16th year. Growth spurts also takelonger to occur. Fifteen to nineteen for boys and fourteen to seventeen forgirls. The mean weight for Sherpas and Quechua is 54 kilograms. Height is 140-160 centimeters. Menses between the Sherpas and Quechua differ. The mean age ofSherpa women to begin menses is 18. For the Quechua it is thirteen although thisis compared to an Andean lowland mean of eleven.
Cold is another stress people of high altitudes must contend with. Threethings help these populations “one is a lack of dramatic fall in coretemperature is a slightly elevated metabolic rate and consistently highextremity surface temperatures(Baker,277).”The elevated metabolic rategenerates a greater body heat. This greater blood flow helps maintain a warmerskin surface. This is necessary because of the heat lost through the extremities.
Keeping the core temperature high is another adaptation which keeps the bodiesof these people warn even while at rest in their harsh environment. There are many non-physical adaptations that people make to help themadjust to the high altitude environment. Clothing is one of these adaptations.
Andean men wear “woolen homespun pants which are mid-calf in length. Worn overone or more layers of loosely knit woolen underwear. A knitted,sleevelessundershirt is used under a cotton shirt with long sleeves…A colorful jacket,matching the pants, is also used. The outfit is completed with a felt hat and aponcho.(Baker,263).”
“Women wear several woolen skirts and a long sleeved jacketof similar material. They also may use knitted underwear but like the men wear amanufactured cotton blouse. Women carry over their shoulders a shawl which issimilar in construction to the poncho…Skirts are usually dark red or black asare jackets(Baker,263).” Footwear is normally not worn. Shoes would bedetrimental during the rainy season because of the extra loss of heat. Also inthe hot weather the feet would sweat.
In the Himalayas “Women are shown wearinglong-sleeved cotton blouses which are covered by woolen jackets and ankle lengthlength skirts. Men’s dress also seems substantial with long jackets,long pantsand heavy coats. As among Quechua Indians most Sherpas name of one group livingin the Himalayas seem to walk barefoot(Baker,261).” There have been nodetailed studies of the Sherpa clothing Houses are another adaptation peoplehave made. In the Andes there are two basic house designs.
“The first uses adobeor sod and is a permanent building. This type is usually found in towns andrepresents a major investment. The second design is constructed of piledfieldstone, is semipermanent, and is cheap to construct It is morecharacteristic of areas where the population is largely pastoral. The adobebuilding has a rectangular floor plan with average dimensions of 5 meters by 10meters. The roof is gabled with a peak of 4 meters to 5 meters from the ground.
Frequently the first meter of the walls will be made of stone to resist erosiondue to rain draining from the roof. The roof is typically constructed of tile,grass, or in more affluent families, corrugated tin. The door is small and it’sheight seldom exceeds 1.3 meters. Doors are usually wooden, but in some casesblankets or old ponchos may be used to cover the openings. Walls are usuallyplastered with mud to form an air right structure.
The roof i s tightly fitted,regardless of the material used. In some cases a wooden floor may be added butusually a natural dirt floor is preferred. Rooms may be employed for cooking ,sleeping, or storage(Baker,260).”For the semipermanent “The floor plan of these houses is circular orrectangular with the upper walls sloping slightly inward. The roof is alwaysconstructed of grass and supported by tree limbs. The diameter is quite variableas is the height. The walls are made of fieldstone. If the house is to beoccupied for an extended period of time the stones are carefully piled toeliminate cracks. Those large holes which remain and those at eye level are usedas windows; that is, they serve to admit daylight and provide for observation ofthe surrounding terrain. These houses may have either a wooden door or a pieceof old cloth may be used to cover the entrance(Baker,259).”
Baker measured theinterior temperatures of adobe houses during the cold and dry season and foundthat well constructed adobe houses could maintain an interior nighttimetemperature 7 degrees Celsius above the ambient temperature. The thermalprotection offered by stone houses seems to be less than that of the adobestructures. Baker reports that there is only 3.7 degrees Celsius differencebetween indoor and outdoor temperatures.
The houses of the Himalayas are “constructed of heavy stone and havewooden roofs which are held in place by stones. Most are two story structureswhose interior dimensions are rather small. They are apparently tightlyconstructed because the first floor is reserved as animals quarters while thesecond is reserved for human habitation. Cooking is done indoors with the smokeescaping from a small hole in the roof. The use of the first floor as animalquarters might add to the insulation between the floor of the human section andthe ground.(Baker,261)” There are no climatological data on these houses.
Scheduling of work is another way people cope. Normally rising afterdawn and “spending the day outside taking advantage of the solarradiation(Moran,160) while working and playing. At sunset everyone goes to sleep. Also at night most families sleep together in bed to share body heat.
The adaptations which have been made by these groups also have a downside to them. There is as we’ve seen a slower growth, a higher infant mortality,and even an increased frequency of respitory diseases. Along with this there isa decrease of many micro-organisms which cause infectious diseases. As weconsider this give and take and whether we would ever subject ourselves to thesethings, we must appreciate what these people go through. High altitude has manystresses to which people must adapt. Although this life is hard the people wouldhave it no other way we should respect and commend them for that.
Bibliography
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- Human Variation. Prentice Hall:New Jersey Monge,Carlos. 1948.
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