Human Variation and Race

HEAT

1. Environment Stress:  Heat can negatively impact the human body in many ways.  First, it can disrupt the homeostasis of one’s body.  Homeostasis refers to the body’s tendency to seek and maintain a condition of balance or equilibrium within its internal environment. When body temperatures reach dangerously high levels it affects many parts of the body.  In the brain, the hypothalamus regulates body temperature; however, extreme heat can impair brain function, which can affect judgment and produces irritability.  The central nervous system is also affected by extreme heat.  When a body overheats, fatigue occurs, slowing down the operation of the brain, nerves, and spinal cord.  Additionally, muscles often cramp and spasm as they attempt to sweat out water and sodium as hyperthermia sets in.  Heat can also cause the heart to beat faster.  As blood vessels dilate to shed heat, blood pressure drops, which triggers the heart to beat faster in an attempt to re-regulate blood pressure.  Even the body’s kidneys are affected by heat.  Heat can cause dehydration because the body is losing moisture as it sweats.   Once dehydration sets in, the kidneys store more toxins that would usually be expelled during urination.

2. Four types of Adaptations to Heat Stress:  Fortunately, the human body has developed adaptations that allow it to stave off environmental heat stress:

Short Term Adaptation:

The human body is equipped with sweat glands that are distributed throughout the skin that allow for evaporative cooling to occur.  As one sweats, the sweat evaporates and cools the body.  This is a useful adaptation, though not foolproof.  High temperatures combined with humid conditions make it harder for the body to sweat and lose excess body heat.  The more moisture in the air, the more difficult it is for sweat to evaporate.

Facultative Adaptation:

Vasodilation is another mechanism the human body utilizes for regulating heat.  Vasodilation allows the capillaries near the skin’s surface to widen in order to increase blood flow to the skin.  This takes the heat carried by the blood away from the body’s interior and allows the heat to be emitted from the surface of the skin.  The visible effect of vasodilation is a flushing or redness of the face and sometimes body.

Developmental Adaptation:

One species-wide adaptation that occurred over numerous generations of human development is the reduction in body hair.  Less hair equates to enhanced cooling effects of sweating.  Our early hominid ancestors were covered with a greater amount of hair on their bodies, however, this adaptation made survival easier in the hot, dry climates of Africa.

Cultural Adaptations:

In addition to adaptations that occur naturally in the human body that enhance survival in excessively hot climates, there are also cultural adaptations that have arisen that make survival in heat more common.  Commercial sports drinks have been created to offset the effects of extreme heat and dehydration.  Sports drinks replenish lost mineral salts in the body and allow for rehydration to occur.  Light, loose fitting clothing has been designed to protect the body from the elements of the sun, but is light enough to allow heat to escape and evaporative cooling to occur; head coverings are also useful tools to reduce exposure to heat and sun.  Sunscreens have been developed to block out harmful UV rays.  People living in remote or undeveloped habitats must seek out shaded/covered habitats to alleviate the extent of heat exposure.  In modern cities, most new homes are built with air conditioning, insulation, and energy efficient windows, all of which allow for cooler temperatures.

3. Benefits of Studying Environmental Stresses that Affect Human Variation:

a)    By understanding our adaptations, we can better understand what mechanisms are in place to protect us when exposed to harsh or unfamiliar climates. 

b)    Studying human variations that are due to environmental stress will allow us to better understand evolution.  By learning about the adaptations that affect humans, we can better appreciate the development and differences between all species.

c)    Environmental impact on human variation also proves that there are no distinctive physical features that are based on race.  The color of one’s skin, for example, has nothing to do with race, and everything to do with melanin levels in the skin.  People who live in regions with a higher exposure to UV radiation have developed higher levels of melanin to protect their skin from ultraviolet radiation, which generally results in darker colored skin.

4. Understanding the Myths of Race Based on Physical Appearances

I could not use race to understand the variations in the adaptations I listed in question two.  The short term, facultative, and developmental adaptations are species-wide adaptations that benefit all humans, regardless of race.  Only the cultural adaptations to heat are affected by region or culture.  By understanding the environmental impact on physical variation allows one to understand that race does not explain the differences in appearance of humans.  To understand that having red skin is not a racial distinction, but rather an adaptation that is attributed to the body’s response to high altitudes allows us to extinguish racial stereotypes from our minds.  Knowledge and understanding of physical adaptations prove that humans are all surprisingly similar; the differences that have arisen are not a result of race, but instead have occurred and have sustained because they have proven to be favorable traits that increase the rate of survival in our species.