Human Variation & Race:

1. The environmental stress from heat negatively impacts the survival of humans by disturbing homeostasis which is the ability to have a stable internal environment regardless of the external environment. The impact of high temperatures can mostly be seen by an excess of evaporative cooling and dehydration. When the weather gets hot (especially extreme temperatures) the human body begins to secrete sweat through the epidermis as a cooling mechanism. Although this strategy is the most important factor in heat dissipation in humans, it can lead to dangerous conditions in terms of water and sodium loss. If a person is going through strenuous activity in high temperatures, they can lose 3 liters of water per hour which will eventually lead to losing 10 percent of body weight which is ultimately life threatening. In order to properly maintain homeostasis in hot temperatures, water must be constantly replinished throughout the body.

2. Adjustment to extreme heat can be seen through short term adaptations. Short term adaptions allow an organism to respond quickly to the climate change in order to maintain homeostasis and only remain until the stress has been removed off of the individual. (1) As previously mentioned, the most popular way humans have adapted to heat stress is through evaporative cooling, the action of secreting sweat outside of the body, ultimately losing water and sodium. (2) Another way humas have adapted to extreme heat is through vasodilation which expands the blood vessels permitting increased blood flow to the skin. Vasodilation permits warming of the skin and facilitates radiation of warmth as a means of cooling. Another important way is by managing body weight. (3) As seen through Bergmann's rule along with Allen's rule, humans with a greater body mass will likely be effected by the heat more as the greater body mass allows for greater heat retention and reduced heat loss. Also, beings with longer appendages, with increased surface relative to body mass, are more adpative in warmer climates because they promote heat loss. According to these rules, the most suitable body shape in these common hot climates is linear, with long arms and legs. (4) As the temperature continues to rise each year, humans have learned that an important way to adapt to heat stress and protect themselves from dehydration is water drinking. It is important to remember that in extreme heat (especially dry) it is necessary to keep drinking water to hydrate the body, regardless whether you are thirsty or not.

                       

3. Modern scientists do not use race to study human variations anymore. Instead they study variation of a particular trait across a cline (a range of environmental stresses such as heat, radiation, etc.) and look for explanations or patterns on how that specific trait is expressed in these various environments. In the twenty-first century, the application of evolutionary principles to the study of modern human variation has replaced the superficial old views of the ninteenth-century view of race based solely on observed phenotype. A benefit of studying the human variation of specific traits over an environmental cline is that traditional classification derived from stereotypes or ideals of a specific race that comprised a specific set of traits, however, typologies are inherently misleading because any grouping always includes individuals who do not conform to all aspects of a particular type/race. Information from environmental cline studies can be useful to aid us in learning more about humans and how they react to environmental stresses.

4. In its most common biological usage, the term race refers to geographically patterned phenotypic variation within a species. When it comes to high temperatures, I do not think that race can help others understand the variation of adaptations previously listed. Clearly, there are phenotypic differences between humans, and some of these roughly correspond to particular geographical locations. (Part 2) It is better that we study the environmental influences on adaptation rather than the use of race because in any so-called racial group, there are always individuals who fall into the normal range of variation for another group based on one or several characteristics. Typologies are inherently misleading because any grouping always includes individuals who do not conform to all apsects of a particular type/race.