Human Variation and Race

 

1. Discuss specifically how high altitude negatively impacts the survival of humans by disturbing homeostasis: 

 

High altitude effects the human body in a variety of ways. The atmosphere is a gaseous envelope that covers the earth. Most physicists, and meteorologists agree that a practical boundary is around 1,000 nautical miles. Without the atmosphere there would be no life on earth. The atmosphere provides protection from harmful ultraviolet (UV) rays, cosmic rays, and meteorites. The atmosphere also protects the earth from extreme temperature variations.  It supports animal and plant life through its gaseous content and provides rain to grow crops. The gaseous atmosphere surrounding the earth is affected by the gravitational pull of the earth. Atmospheric pressure is the combined weight, or force, of all the atmospheric gases exerted at any given point.  As you ascend from sea level, the atmospheric pressure will correspondingly drop. As atmospheric pressure drops, the air becomes less dense. The primary issue with altitude is hypoxia, caused by both the lack of pressure and the decrease in oxygen. Secondary stresses of high altitude include cold, low humidity, and increased ultraviolet radiation. The low humidity is what contributes to the body’s fluid loss. Lower atmospheric pressure results in lower hydrostatic pressure. This is the pressure that keeps your fluid in a fluid (i.e. non-gaseous) state. At a high enough altitude, or low enough pressure, your bodily fluids will boil. Not due to an increase in temperature but due to a decrease in pressure. They convert to a gaseous state. Humans are aerobic machines, which is to say, we use oxygen in our energy production cycle. The human body adjusts well to moderate hypoxia, but ultimately hypoxia will result in death. The lower atmospheric pressure can also lead to pulmonary edema (HAPE) and cerebral edema (HACE), both of which are rare, but still quite deadly.  Finally, people taking certain medication or with pre-existing medical conditions, including heart failure, sickle cell anemia and even diabetes may experience an exacerbation of their illness.

2. Identify 4 ways in which humans have adapted to this stress:

 

(1.) Increased heart rate and respiratory rate are short term reactions to hypoxia. These two reactions coupled with fatigue help control your oxygen supply and demand.  You use less oxygen moving slowly and your metabolism attempts to accelerate its oxygen acquisition and distribution.  

At first we feel terrible and are unable to mount a reasonable physiologic response.

 














  
  

(2.) Over a short period of time, however (several days,) humans will have a longer term physiological  response to high altitude hypoxia.  Additional erythrocytes and capillaries are produced and carry more oxygen.

 

         
When a person acclimatizes to high altitude this is an example of facultative response.  This is a more efficient physiological response than in the short term.   

 (3.) Some populations indigenous to high altitudes have developmental adaptations. Greater hemoglobin content and greater vital capacity are two examples of this.  Natural selection has produced peoples specifically adapted to higher altitudes.  This is a permanent, heritable response.

 

 

Correlation betweenV˙o _{2 max} and CO_max in both Tibetan adolescents and Han adolescents

(4.) Humans have adapted to high altitude with a variety of strategies.  Cold can be combatted with warm clothing, and limiting outside activity to the warmest part of the day.  These are cultural practices.  These also help with the loss of atmospheric pressure by limiting fluid loss through the skin and lowering oxygen demand through limiting activity.

3.  What are the benefits of studying human variation from this perspective across environmental clines? Can information from explorations like this be useful to help us in any way?

 

The benefits of studying human variation are endless.  Not only do we understand adaptive reactions to stressors we better understand what physiologic strategies are typically employed to overcome different challenges. When a physician sees a patient display the symptoms of increased heart rate, rapid breathing and cyanosis he recognizes immediately that the person is hypoxic.  

 Professional cyclists notice that people from high altitudes appear to have greater stamina. Cyclists then train in high altitude to increase their performance; exercise physiologists wonder why.  This is the beginning of a cycle, no pun intended, where they discover that the cyclists have more erythrocytes as a reaction to their altitude training. This, in turn, leads a researcher to uncover that they stimulate the creation of a factor, erythropoietin, in their blood that causes this increase. 

This erythropoietin is isolated and other colony stimulating factors are discovered.  Macrophage, leukocyte and granulocyte factors are discovered.  Erythropoietin is used for people in kidney failure, renal dialysis, HIV infection and cancers.  It can be life saving for chemotherapy patients who suffer from the loss of their oxygen carrying red cells.  Stem cell and bone marrow transplants and transfusions are made possible by many of these drugs. They are given to the donors to increase their hepatocyte counts making a harvest possible.  What good could come of it, you ask.

4.  How would you use race to understand the variation of the adaptations you listed in #2? Explain why the study of environmental influences on adaptations is a better way to understand human variation than by the use of race. 

Race is an imprecise stratification. Separating individuals by shoe size may also reveal a genetic correlation but this is also an imprecise method.  Factors that are more visibly evident do not necessarily indicate the underlying genetic components. 

 




 
The examples in question #2 are evidence of just this circumstance.  While all of the individuals with high altitude developmental adaptations in Peru may be Peruvians, not all Peruvians share these adaptations.  Further, the Tibetans have high-altitude developmental adaptations but are not Peruvian. The two high altitude peoples likely share some cultural adaptations and probably share some level of similarity of physiognomy.  This could possibly cause us to conclude that they are related racially were it not for the geography.  This error is because race is a human construct of visible similarity.