Human Variations in High Altitude Populations

“Some ten to twenty-five million people (that is less than 1% of the earth’s population) currently make it[high altitude zones] their home(Moran,143). ” The adjustment high altitude populations must make are firstly physical and secondly cultural. Although most people adapt culturally to their surroundings, in a high altitude environment these cultural changes alone aren’t enough. Many physical adaptations that reflect “the genetic plasticity common to all of mankind(Molinar,219)” have to be made to survive and even more than that thrive in this type of environment.

In this paper I will describe the high altitude stresses. Along with adaptations made by the populations living in them. The two high altitude populations which I will examine in this paper are the Tibetan people of the Asian Himalayas and the Quechua of the South American Andes. The Quechua are an Indian people who inhabit the highlands of Peru and Bolivia. They speak Quechua, which is a branch of the Andean-Equitorial stock. They show many remnants of Inca heritage by their houses, music, and religion which has pagan rites under the Roman-Catholic surface. Their villages consist of kin groups .

Their marriage partners are taken from within each village. Agriculture is the dominant subsistence pattern in the central Andean region but the Nunoa region where the Quechua reside can only support a few frost-resistant crops. Which include bitter potato, sweet potato, and a few grain crops of quinoa and canihua. The rest of the fruits and vegetables of the Quechua come from the eastern mountains on it’s way to the markets. The most important subsistence pattern for the Quechua is stock raising. Which is limited to the few animals that do well in the high altitudes.

Their stock include alpacas,llamas and sheep. In the Himalayas only “5% of the geographical area(Baker,36)” can be sed for agriculture. The main crops are barley, wheat and buckwheat. The crops are grown between 3,500 and 4,300 meters. These few crops are threatened by drought, hail, frost, snow and erosion. The Himalayas also have extensive pasture areas which are used by the nomadic and sedentary peoples. The higher regions have pastures where yak, sheep, and goats are the main animals used. In the high altitude there are many environmental stresses that the people must endure.

They include hypoxia, intense ultraviolet radiation, cold, aridity, and a limited nutritional base. The people adapt to these stresses in many ways. Hypoxia, or low oxygen pressure, is the most prominent stress which populations living at high altitudes must deal with. “Hypoxia results whenever either physiological,pathological, or environmental conditions cannot deliver adequate supply of oxygen to the tissues. Since air is compressible, air at high altitudes is less concentrated and under less pressure. At 4500 meters the partial pressure of oxygen is decreased by as much as 40%, in comparison to pressure at sea level.

This reduces the amount of oxygen finally available to the tissue(Moran,147-148). ” The adaptations to hypoxia are all geared towards ncreasing the oxygen to the tissues. One adaptation to hypoxia is an increase of red blood cells in circulation. 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. “This greater number of red blood cells increases the hemoglobin concentration, which in turn increases the oxygen -carrying capacity per unit volume of blood(Molinar,219). ” This then increases the oxygen sent to the tissues.

Respiration and cardiac output are also increased. There is an increase in the capillary network to aid diffusion of oxygen to the tissues. There have also een cellular changes that increase the resistance to the tissues to low oxygen. Many other effects are felt from hypoxia. Growth and development are one of the many areas affected. Kruger and Arias-Stella compared two populations at 4,570 meters and at 200 meters and found the mean placental weight of the high population to be 561 grams as compared to the low-land population weight to be 500 grams.

Placenta volumes did not differ showing that the placenta at the high altitude was denser. The denser placenta offers the fetus more protection and greater oxygen. The birth weights at high altitudes are uniformly lower than hat of low altitude. This is probably due to hypoxia but the nutritional status of the mother’s must also be taken into account. A study by Frisancho Velasquez and Sanchez demonstrated that subjects with short stature attained a greater maximal aerobic capacity than their counterparts of a larger body size when tested under identical conditions.

It is known that ” birth weight is said to be correlated with maternal size particularly stature(Baker,95)” therefore small birth weight is an effect of the adaptation of body size to deal with hypoxia. Growth and development in high altitude populations is considerably lower than low-land growth. This may be due to the growth of their large chests and the extra production of the red blood cells from the bone marrow. This extra large chest growth increases the lung capacity to take in more oxygen. Although in 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 take longer to occur. Fifteen to nineteen for boys and fourteen to seventeen for girls. The mean weight for Sherpas and Quechua is 54 kilograms. Height is 140-160 entimeters. Menses between the Sherpas and Quechua differ. The mean age of Sherpa women to begin menses is 18. For the Quechua it is thirteen although this is compared to an Andean lowland mean of eleven. Cold is another stress people of high altitudes must contend with.

Three things help these populations “one is a lack of dramatic fall in core temperature 2) is a slightly elevated metabolic rate and 3) consistently high extremity surface temperatures(Baker,277). ” The elevated metabolic rate generates a greater body heat. This greater blood flow helps maintain a warmer skin surface. This is necessary because of the heat lost through the extremities. Keeping the core temperature high is another adaptation which keeps the bodies of these people warn even while at rest in their harsh environment.

There are many non-physical adaptations that people make to help them adjust to the high altitude environment. Clothing is one of these adaptations. Andean men wear “woolen homespun pants which are mid-calf in length. Worn over one or more layers of loosely knit woolen underwear. A knitted,sleeveless undershirt is used under a cotton shirt with long sleeves… A colorful jacket, atching the pants, is also used. The outfit is completed with a felt hat and a poncho. (Baker,263). ” “Women wear several woolen skirts and a long sleeved jacket of similar material.

They also may use knitted underwear but like the men wear a manufactured cotton blouse. Women carry over their shoulders a shawl which is similar in construction to the poncho… Skirts are usually dark red or black as are jackets(Baker,263). ” Footwear is normally not worn. Shoes would be detrimental during the rainy season because of the extra loss of heat. Also in the hot weather the feet would sweat. In the Himalayas “Women are shown wearing long-sleeved cotton blouses which are covered by woolen jackets and ankle length length skirts. Men’s dress also seems substantial with long jackets,long pants and heavy coats.

As among Quechua Indians most Sherpas [name of one group living in the Himalayas] seem to walk barefoot(Baker,261). ” There have been no detailed studies of the Sherpa clothing Houses are another adaptation people have made. In the Andes there are two basic house designs. “The first uses adobe or sod and is a permanent building. This type is usually found in towns and represents a major investment. The second design is constructed of piled fieldstone, is semipermanent, and is cheap to construct It is more characteristic of areas where the population is largely pastoral.

The adobe building has a rectangular floor plan with average dimensions of 5 meters by 10 meters. 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 erosion due 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’s height seldom exceeds 1. meters. Doors are usually wooden, but in some cases blankets or old ponchos may be used to cover the openings.

Walls are usually plastered with mud to form an air right structure. The roof is tightly fitted, regardless of the material used. In some cases a wooden floor may be added but usually 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 or rectangular with the upper walls sloping slightly inward. The roof is always constructed of grass and supported by tree limbs. The diameter is quite variable as is the height. The walls are made of fieldstone.

If the house is to be occupied for an extended period of time the stones are carefully piled to eliminate cracks. Those large holes which remain and those at eye level are used as windows; that is, they serve to admit daylight and provide for observation of the surrounding terrain. These houses may have either a wooden door or a piece of old cloth may be used to cover the entrance(Baker,259). ” Baker measured the interior temperatures of adobe houses during the cold and dry season and found hat well constructed adobe houses could maintain an interior nighttime temperature 7 degrees Celsius above the ambient temperature.

The thermal protection offered by stone houses seems to be less than that of the adobe structures. Baker reports that there is only 3. 7 degrees Celsius difference between indoor and outdoor temperatures. The houses of the Himalayas are “constructed of heavy stone and have wooden roofs which are held in place by stones. Most are two story structures whose interior dimensions are rather small. They are apparently tightly constructed because the first floor is reserved as animals quarters while the econd is reserved for human habitation.

Cooking is done indoors with the smoke escaping from a small hole in the roof. The use of the first floor as animal quarters might add to the insulation between the floor of the human section and the ground. (Baker,261)” There are no climatological data on these houses. Scheduling of work is another way people cope. Normally rising after dawn and “spending the day outside taking advantage of the solar radiation(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 down side 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 is a decrease of many micro-organisms which cause infectious diseases. As we consider this give and take and whether we would ever subject ourselves to these things, we must appreciate what these people go through. High altitude has many stresses to which people must adapt. Although this life is hard the people would have it no other way we should respect and commend them for that.

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