Human Variation and Race

Hot climates can be very detrimental to human homeostasis.  When exposed to heat for long periods of time, the human body can lose up to half a gallon of water each thirty minutes through sweating, resulting in rapid dehydration.  Heat exhaustion, the loss of bloodflow to the internal organs due to an increase of bloodflow to the skin, and heat stroke, where the body's internal thermostat stops functioning, both result from prolonged exposure to heat.  If these unhealthy effects are left untreated, this can cause the body's core temperature to pass a safe limit, resulting in hyperthermia.  This leads to the failure of the internal organs and potential death.

Four human adaptations in response to hot climates are:

• A larger body surface area, which is a developmental adaptation.  According to the findings of biologist Joel Allen, mammal populations in warm climates near the equator had longer limbs than those living farther from the equator, in colder climates.  The same characteristics are found in human populations in the same regions; an example of this is the Samburu in Northern Kenya, who possess long limbs and a more linear body shape.  This is because a larger body surface area, created by longer limbs, allows humans to release larger amounts of body heat at a given time, so they can say cool in hotter climates.

 The Samburu (above) possess long limbs and linear bodies, providing a larger

bodily surface area from which excess heat can be released.

• Sweating, which is a short term adaptation.  A period of sweating only lasts as long as the heat is present, and will stop once the climate has changed (and the external and internal temperatures have gone down).  This is also known as evaporative cooling, and while it is effective for short amounts of time, the water and minerals lost by sweating will eventually need to be replenished.

Sweating is essential to keeping the body cool in hot temperatures, especially

during periods of physical exertion.

• The change of salt concentration within sweat, which is a facultative adaptation.  Once a person is exposed to high levels of heat for a long period of time, eventually the concentration of salt in their sweat will decrease, allowing it to last longer in their body, while the amount of water released through perspiration increases.

Although I don't have an image depicting the salt concentration within sweat, I gathered my information from the anthro.palomar.edu website, as well as one outside source.  Below is a graph from the Journal of Applied Physiology, which shows the findings of a study meant to "determine the effect of active heat acclimation on the sweat osmolality and sweat sodium ion concentration vs. sweat rate relationship in humans."  The study followed eight males over a 10-day period, who exercised each day in hot weather.  The graph shows that while the sodium ion concentration in their sweat decreased over the 10 days, the sweat rate increased.

Source: http://jap.physiology.org/content/103/3/990

• The use of air conditioning and insulated shelter, which is a cultural adaptation.  This type of adaptation has nothing to do with the workings of the human body; however, shelter and conditioned air provide external barriers from heat.  A structure with an insulated roof and walls prevent heat from coming into the structure and cool air from escaping.  An air conditioning unit cools the air within the structure, allowing the body to cool down and maintain a proper temperature.

The ice blocks which make up igloos contain air pockets, which provide effective

insulation.  When warmed by body heat, the internal temperature of an igloo

can surpass the outside temperature by over 100 °F.

Air conditioning units collect air from outside a structure, cool it, and pipe it 

into the structure, producing an artificial climate inside.

By widely studying human variation, we can see the ways in which humans adapt to conditions, and in some cases how quickly they are able to adapt.  By using these findings, we are able to predict human evolutionary patterns resulting from certain environmental stresses.  In the case of heat acclimation, we can use the information gathered from people who are naturally more able to operate in a hotter climate, and use this information to create new technologies which help those who are not fit for these climates survive in them.

The idea of race comes from the physical differences expressed in humans.  Although we are all of the same species, we categorize ourselves by the shade of our skin, our facial structures, our body types, and so forth.  However, our real differences don’t stem from race itself—race is a byproduct of human adaptation.  Because groups of humans in different geographic locations managed to adapt to different environmental influences, their very appearances became different.  The variations resulting from a hot climate are a good example of these differences: those in hotter climates may develop a taller, more linear body structure to increase bodily surface area than those in colder climates, who may be shorter and stockier to retain body heat.  How these variations came to be, and the environmental conditions they are suited for, is a better way of mapping the differences between human populations than the variations themselves.  The decision to categorize people using these physical differences, these variations, is not scientific—it is a social decision, based on a desire for generalization.