Index
The human body responds quickly to changes in environmental stress in various biological and cultural forms.
We can acclimate to a wide range of temperatures and humidity. When traveling at high altitudes, our bodies adjust so that our cells continue to receive enough oxygen.
We also respond physiologically to internal and external stresses such as bacterial and viral infections, air and water pollution, imbalance in diet, and overcrowding.
This ability to adapt quickly to changing environmental conditions has made it possible for us to survive in most world regions.
We live successfully in tropical rainforests, deserts, Arctic moors, and even densely populated cities with considerable pollution.
Most other animal and plant species are limited to one or relatively few environments since their adaptive capacity is more limited.
Humans typically respond to environmental stresses in four ways:
- Genetic change
- Development adjustment.
- Acclimatization.
- Cultural practices and technology.
Genetic change
When environmental stress is constant and lasts for many generations, successful adaptation can be developed through biological evolution.
Individuals who inherit a trait that offers an advantage in responding to particular stresses are more likely to survive longer and pass more of their genes to the next generation.
This is the evolution by natural selection.
For example, a genetic solution to environmental stress is our ability to produce sweat as an aid in cooling our bodies in hot environments.
No wonder we have this ability because our immediate pre-human ancestors were tropical animals.
Genetic change in response to environmental stress usually takes many generations to spread in a population.
Fortunately, we also have other ways to respond more quickly as individuals during our own lives.
The word adjustments are used here to refer to these short-term physiological changes that are not inheritable. The adaptations of the word are reserved for heritable genetic changes developed in a population over a long period.
Development adjustment
One of the most potent types of adjustments to environmental stresses is a change in the patterns of growth and development.
This occurs in childhood and typically results in anatomical and physiological changes that are primarily irreversible in adulthood.
Such permanent changes refer to development adjustments or development acclimatization.
Among humans, development adjustments result from natural environmental pressures and cultural practices.
An example of the latter was the now-illegal practice in China of tightly wrapping girls’ feet with a cloth to impede average growth.
While this caused paralysis of the growth of the foot bones, it also resulted in tiny feet that were considered very attractive.
What makes these kinds of adjustments possible to the parts of our body is the fact that human beings have a high degree of physiological plasticity.
It can be molded physically by our environment during the growth process.
Adults are the result of genetically inherited traits modified as we grow.
Acclimatization
All other forms of adjustment to environmental stress are usually reversible if they occur in childhood or adulthood.
These reversible changes are known as acclimation. It is helpful to consider the different forms of acclimatization in terms of the length of time they may occur.
Forms of acclimatization
An example of long-term acclimatization is people who lose excess body fat and are very thin due to mild or long-term malnutrition.
If they later increase their diet to a constant level of excess calories, they are more likely to retain more body fat and eventually become obese.
Thus, they experience long-term acclimatization when they initially lose body fat and later when they retain it. In both cases, they are acclimated to the supply of available food.
Anatomical and physiological adjustments can also be developed for even shorter periods.
For example, many people acquire dark tans from the skin during the summer months and lose them during the winter.
This change in skin coloration is seasonal acclimatization to the destructive effects of the sun’s ultraviolet radiation.
When traveling to a great height, it is common to experience a progressive decrease in the ability to hear due to uneven pressures from one side of the eardrum, causing it to swell a little on the outside and become less flexible.
This difference in the pressure observed in the mountains can usually be nullified by yawning, swallowing, or chewing gum.
However, it is often difficult to equalize the pressure when climbing great heights if someone has a congested nose.
As a result, they are susceptible to considerable pain in their ears.
The difference between the types of acclimatization is not only in the amount of time it takes for the adjustment to occur initially.
In general, the shorter the time for acclimatization, the quicker it is also in the reversal once the environmental stress is no longer present.
Combined effects
Genetic adaptation and the three types of adjustments to environmental stresses are not always different phenomena.
The acclimatization in childhood can lead to permanent anatomical changes, as is often the case with malnutrition.
When an acclimation can achieve good health and longevity, it can give people a selective advantage in transmitting their genes to the next generation.
This can have a substantial determining effect on the direction of evolution. Genetic change can play an essential role in the adjustment since the capacity for acclimation ultimately depends on the genetic makeup.
The ability to adapt to specific environmental stress varies from person to person and from one population to another. We are not all biologically equal.
For example, some groups of people are more successful in adjusting to high altitudes. Others can better handle intense heat and high humidity.
Adaptation responses tend to occur in space groups around the world.
The most efficient adaptations for specific environmental stresses are found in areas where priorities are most common.
This is evidence that natural selection has occurred in the population by adapting successfully.
Cultural practices and technology
It is important to remember that human beings not only interact with their environments biologically. We use culture too.
In the last half a million years at least, we invented the technological aids that allowed us to occupy new environments without first evolving the biological adaptations.
Houses, clothing, and fire allow us to ultimately live in the Arctic and temperate regions, even though we essentially have tropical animal bodies.
However, this does not mean that technology by man eliminates the adaptive biological advantages of particular individuals or groups.
