Human Variation and Race

1. Select only ONE of the following environmental stresses: (a) heat, (b) high levels of solar radiation, (c) cold, or (d) high altitude. Discuss specifically how this environmental stress negatively impacts the survival of humans by disturbing homeostasis.

High levels of solar radiation is an environmental stressor which negatively impacts the survival of humans by disturbing homeoastasis.  UVA radiation has the ability to penetrate through the epidermis all the way to the dermis layer, while UVB radiation penetrates only to the epidermis layer.  The only benefit from exposure to UV radiation is the stimulation of vitamin D production by UVB waves.  When we are sunburned, UVB and UVA rays cause short-term suppression of the immune system.  Overexposure to UVB radiation, which is directly absorbed by the DNA within cells, can potentially cause genetic damage leading to skin cancer, it is the more harmful of the two types of UV radiation.  This damage at the genetic level disturbs homeostasis and is life threatening to the species.

2. Identify 4 ways in which humans have adapted to this stress, choosing one specific adaptation from each of the different types of adaptations listed above

Short Term

A short term adaptation to overexposure from UVB/UVA rays is a sunburn.  A sunburn let’s us know that we have been in the sun too long and that further exposure will be harmful to the skin and to the DNA in our cells.  Fair skin is more apt to sunburn than darker skin as darker skin already contains a higher concentration of melanin which protects us from the UV solar radiation.  Light skinned people do not produce as much melanin, so therefore they will get a sunburn faster than dark skinned people.

Facultative

A facultative adaptation to protect us from the harmful UVB radiation waves is skin tanning.  Tanning happens when exposure to sunlight triggers a protective mechanism through increased melanin production in the epidermis layer.  Melanin is a natural sunscreen produced by our bodies and the tanning response will remain until the overexposure to UV rays is reduced.  As we spend more time in the sun during the summer months with the warmer weather, it is common to see people of both fair and dark skin have a darker complexion and then to have their complexion return to normal during winter months. 

Albinos are the only human beings who carry a genetic mutation preventing their bodies from producing melanin.  Many people of northern European descent with very fair skin, blue eyes and light hair produce very small amounts of melanin.  Without the ability to tan, their skin alone will not protect them from UV radiation. 

Developmental

A developmental change is found in populations which have a higher concentration of people with darker skin.  Dark skin contains higher concentrations of melanin, which is a natural sunscreen protection for the skin.  Populations with the most exposure to the sun’s harmful rays are located in Savannah’s and plains (mostly in African and Tropical climates).  Therefore we can see a direct correlation geographically in those regions having a higher density of people with darker skin.  Even people with darker skin can tan and sunburn.  This is because a certain amount of UV radiation is necessary for the production of Vitamin D in the body.  Too much exposure to solar radiation results in skin cancer, but too little exposure can result in a Vitamin D deficiency which can affect the body’s ability to process calcium and weaken the bones.  Populations without enough sunlight can develop diseases such as rickets, where the bones are not strong enough to support the weight of the body as it grows.  So, lighter skinned populations do not produce as much melanin because the l

esser amount of sunlight they receive is needed to obtain enough Vitamin D to prevent other diseases. 

Cultural

A cultural adaptation to the harmful UVA and UVB rays is advent of clothing, shelter and in modern history, sunscreen lotions.  Shelter and clothing made it possible for our ancestors to limit their exposure to the sun’s radiation and therefore reduced the need for such high levels of melanin production.  Migrating to other environments such as forested areas also reduced our ancestor’s time in the sun.  Over time, we can see the change in skin pigmentation with the lighter skinned populations possessing more of the northern geographical regions and darker skinned populations possessing more central and southern regions closest to the equator.  Today people of all skin pigments now populate all regions of the globe.  Outdoor sporting activities have also increased our time in the sun.  But, rather than migrate northward if you are light skinned, the invention of sunscreen lotion can protect you for longer periods of time in the sun.  However, it is not a solution that completely prevents skin cancer for either light or dark skinned people.  Too much time in the sun increases our risk of skin cancer, no matter the

color of our skin.

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? Offer one example of how this information can be used in a productive way.

The benefits of studying human variation in this manner is that by studying the changes of various sample populations over time, we can evaluate and see the environmental stressors, which can affect any population.  If we took one population with one group of traits and moved them to another environment than the one in which they were born, eventually, we would see an evolutionary adaptation to the new environment.  For example, studying the high rate of sickle cell anemia in black populations can help scientists to identify and come up with treatments and hopefully cures that will help other people with sickle cell anemia, not just one population.  Studying rickets in fair skinned populations can help us understand the need for sunlight and how much sunlight is necessary to avoid the disease.

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. 

I would use race only to classify geographic groups of people who have the same or similar set of adaptations to the same environment.  In this way, we can see how our ancestors developed and changed over millions of years and understand our origins more fully.  It also can help us to predict what changes might occur in the human population given certain environmental stressors.

When studying the environmental influences of a group of people over long periods of time, we will begin to see patterns which evolved as adaptations to those outside stressors.  Some adaptations (such as being born with lighter or darker skin) become permanent, while others will remain until the stressor has been removed (such as tanning during the summer with increased sun exposure).  This ability to adapt and change is inherent in the entire human race and therefore connects us more closely at a genetic level than any of the outward differences we may see.  It helps us to see that our differences are simply responses to our environment and not that we are completely different species from one another, evolved from completely different ancestors.  I feel that being able to study the human species in this manner is a great tool to helping people overcome racism and see more of the ways we are alike than the ways in which we differ.