Author : Wahid Ahmad
Adaptations to High Altitude
High-altitude zones have been inhabited
by human populations since ancient times, despite the initial challenges
newcomers face, such as:
Most high-altitude areas lie within 40
degrees of the equator, where sunlight is abundant and productivity is higher.
These regions include:
High-altitude regions are unique for
researchers studying human biology and ecology because they require
physiological and genetic adaptations due to the lack of oxygen (hypoxia).
These adaptations take precedence over behavioral adjustments.
Mountainous areas have diverse
ecosystems, with distinct plant and animal communities distributed in vertical
zones. As elevation increases, vegetation and wildlife change rapidly, forming
different biomes and transitional zones known as ecotones.
Living at high altitudes presents
various challenges, including low oxygen levels (hypoxia), cold temperatures,
dryness, poor soil, steep terrain, and limited biological productivity. People
in these areas often face additional difficulties due to poverty and inadequate
infrastructure.
Adaptations
To cope with cold stress at high
altitudes, people use warm clothing, seek shelter, and schedule activities to
maximize time in the sun. Additionally, they undergo developmental adjustments
like non-shivering thermogenesis and increased blood flow to extremities to
better adapt to the cold.
To deal with low productivity,
high-altitude populations employ various strategies such as seasonal migration,
marriage practices that spread out the population, integrating agriculture and
animal husbandry, cultivating diverse crop varieties, minimizing sexual
division of labor, and managing land collectively. This diversity and
organization help protect against the unpredictable nature of mountain
ecosystems.
Children often take on tasks like
herding to reduce the caloric needs of households, thus conserving energy at
the population level.
Adaptations
to low oxygen levels
At high altitudes, the most significant
challenge for human populations is hypoxia,
or low oxygen pressure. This occurs because the air at high altitudes is
less concentrated and under less pressure compared to sea level, leading to a
reduced amount of oxygen available to tissues. Hypoxia can result in various
physiological and environmental conditions that hinder the delivery of
sufficient oxygen to tissues.
While cultural practices cannot
increase oxygen levels, some associated problems, like difficulties in
pregnancy and high neonatal mortality rates, have been managed through factors
like diet, work patterns, and cultural attitudes toward reproduction.
Individuals and communities living at
high altitudes exhibit various adaptive mechanisms to cope with hypoxia. These
adaptations involve:
· Increasing oxygen supply and pressure
at the tissue level.
· Physiological adjustments include
increased lung ventilation,
· Enlargement of the capillary bed,
· Chemical changes related to internal
respiration. For example, Tibetans have been found to possess larger chest
circumferences and lung volumes compared to lowland populations, suggesting
developmental adaptations to hypoxia.
Figure 1.1. Schematic
Summary of the Adaptive Responses (Physiological) to Hypoxia
Source: R. Frisancho, “Functional Adaptation to High Altitude Hypoxia,”
Science 187 (1975): 313–319. Copyright 1975 by the American Association for the
Advancement of Science.
Pulmonary ventilation
At high altitudes, a common response
among both native populations and newcomers is an increase in pulmonary
ventilation, leading to a 20–40 percent faster breathing rate compared to sea
level populations. Surprisingly, this higher breathing rate in native
populations doesn't lead to an increase in metabolic rates. The reason behind
this phenomenon is not fully understood, but it seems to be related to chemical
stimulation by blood carbon dioxide levels.
Newcomers to high altitudes may
experience symptoms such as:
· breathlessness,
· dizziness,
· headaches due to the body's adjustment
to the lower oxygen pressure.
Hyperventilation
can exacerbate these symptoms by causing hypocapnia.
Chronic mountain sickness (CMS) is a
condition associated with prolonged exposure to low oxygen pressure, with a
lower incidence observed in Tibetans compared to Andean populations, possibly
due to genetic adaptations to hypoxia.
People who live
in high places have larger lungs compared to those who live at lower altitudes.
This happens because their lungs grow differently during childhood. More small
air sacs, called alveoli, develop in their lungs, increasing the surface area
for breathing. This helps them take in more oxygen from the air.
Polycythemia
Characterized by an increase in red
blood cells and hemoglobin, is another adaptation to high altitude. This
condition develops shortly after birth in response to prolonged exposure to
hypoxia, leading to increased oxygen-carrying capacity in the blood.
Tissue-Level Adaptations:
Enlargement of Capillary Bed: In response to chronic hypoxia,
tissues may undergo angiogenesis, the formation of new blood vessels
(capillaries), to increase their vascularity. This process enhances oxygen
delivery to tissues by increasing the surface area available for oxygen
exchange.
Chemical-Enzymatic Changes
Within cells, adaptations occur to
optimize oxygen utilization and maintain cellular function under hypoxic
conditions. These changes can include alterations in metabolic pathways, enzyme
activity, and gene expression to support cellular respiration and energy
production despite reduced oxygen availability.
Living at high altitudes also exposes
individuals to additional stressors such as greater ultraviolet radiation,
rapid heat loss, and dry conditions. Understanding these multiple stresses is
crucial for comprehensively studying the adaptability of high altitude
populations.
Dietary
adaptations to high Altitude
· Physical Capacity at High Altitudes
Natives perform better than newcomers
at high altitudes due to lifelong exposure and physical training, which
increase maximal oxygen consumption. This capacity is comparable to athletes.
They exhibit efficient oxygen
diffusion, marked economy in oxygen use, and enhanced work capacity due to
childhood development and high activity levels.
· Dietary Factors
A high-carbohydrate diet is common among
high-altitude natives and is thought to enhance endurance through increased
muscle glycogen.
Coca chewing, a traditional practice,
is believed to aid in managing hypoglycemia and carbohydrate malabsorption. Coca
chewing is associated with higher glucose levels, potentially due to
stimulation of glycogen stores and improved carbohydrate absorption in the
intestines.
While high-altitude populations may
experience iodine deficiency and goiter, they have a lower prevalence of type
2 diabetes, likely due to high physical activity levels and low plasma
insulin concentrations.
Reproduction and Maturation
High altitude hypoxia affects
reproduction and maturation. Initially, it was thought to hinder pregnancies
due to "thin air," causing high neonatal mortality. Research later
showed reduced fertility and difficulties carrying fetuses among newcomers, but
native populations adapt better. Adaptations include larger placentas to aid oxygen delivery, though birth weight
decreases relative to placenta size.
Despite challenges, populations like
the Quechua prioritize large families, utilizing enlarged placentas. However,
some face chronic mountain sickness (CMS), resulting in excessive polycythemia
and requiring medical intervention or migration.
|
Box 1 Quechua refers to both an indigenous ethnic group and a
family of languages spoken primarily in the Andean region of South America.
The Quechua people are one of the largest indigenous groups in South America,
with significant populations in countries like Peru, Ecuador, Bolivia, and
parts of Colombia, Argentina, and Chile. They have a rich cultural heritage,
with traditions, customs, and practices that have persisted for centuries. |
Children at high altitudes experience
slower maturation due to chest and bone marrow demands and calorie diversion to
heat production. Malnutrition exacerbates issues, with stunting and underweight
prevalent.
Overall, while high altitude hypoxia presents
reproduction and maturation challenges, populations like the Quechua adapt,
though not all individuals succeed, leading to conditions like CMS.
Malnutrition worsens these challenges.
Reference
Moran, E. F. (2022). Human adaptability: An introduction to ecological anthropology. Routledge.