Human Adaption to the Environment---Solar radiation

1. Solar radiation can negatively impact the survival of humans by disturbing homeostasis especially if solar radiation is high. Let’s look more closely at the Sun; it emits short-wave ultraviolet radiation (UVR) that is potentially harmful to life.  It therefore can be said UVR is a force of evolution whereas humans had to adapt to the environmental stress of UV radiation or perish.  For example, as overexposure to solar or UVR it causes skin cells to mutate creating cancer cells and therefore cancer.  Aside from cancer, if high levels of UV radiation are exposed to a person’s skin it causes a breakdown of B vitamin, a folate. Women, men, and children are all sensitive to folate levels and as such it can cause all different side effects. For women who are pregnant they are prescribed vitamins with enough folic acid to decrease the risk of miscarriages and prevent defect in babies such as neural tube defects. Earlier in their stages of pregnancy, folate is an essential vitamin for the process of DNA replication.  For men, a lack of folate can result in a reduction in the production of sperm cells. Lastly, increased sunlight exposure increases the chance for children to develop multiple sclerosis. Looking at skin color, light-colored skin favors production of vitamin D in northern latitudes, whereas darker colored skin can prevent people from producing enough vitamin D (necessary for Ca absorption)resulting in rickets disease in kids and osteoporosis in adults.

*Darker skin more prone to frostbite than lighter skin

2.

 A. Short Term

Unfortunately, there isn't a short term adaptation to solar radiation making it a dangerous stress especially for individuals with low levels of melanin. 

B. facultative adaptation

An example of a facultative adaptation is tanning. The physiological response to this environmental stress is influenced to an extent by duration and severity of the exposure. The simplest form of accommodation is tanning; it is a quick and temporary response due to external environmental changes.  As an example, increased exposure results in tanning and a decrease in exposure over time the skin will revert to its original color. Simply put, by increasing the number of melanin granules and the percent of different variations of melanin is responsible for a tan.

C. developmental adaptation

Melanin can have protective qualities against the harmful effects of solar radiation which is a developmental adaption.  So what determines skin color is the next question, the answer would be the number and size of melanin particles.  For instance, an individual with a higher ratio of pheomelanin their skin will tend to be more red to yellow color based.  

Individuals who have a higher percentage of eumelanin their overall hue will be more dark brown to black tint.

Studying human variation in this manner is beneficial because it expresses environmental stresses and teaches us how various populations adapt to them. This information can be used to understand why fair skinned races are more susceptible to skin cancer then dark skinned races. It also helped in the development of sunscreen lotion which is an artificial version of melanin.  Races that express the trait for dark complexion are genetically favored by natural selection when it comes to solar radiation.

D. Cultural adaptation

Solar radiation is so damaging that our body can’t react fast enough other than physically seeking shelter when the sun is out when there is nowhere to go for shade.  Adaptations such as wearing hats etc. are more behavioral than any other type of adaption.  Examples of cultural adaptations are sunglasses, hats, clothes and sunscreen.  Before people spend a day in the sun, they will usually apply sunscreen to prevent or reduce risk of skin damage and tanning.  People also wear sunglasses, hats and extra clothing (beach cover-up) to protect them from solar radiation.

3. The study of the gradual change of a species' traits across different populations is beneficial because it shows why certain people have health problems, or are healthier than others or have the skin tone they do, or why it is beneficial to have the skin tone that they do. By looking at the clines of solar radiation (where melanin is protective against UV) versus the need for vitamin D absorption (where melanin is not protective against UV) shows that in areas where UV protection is needed, skin color is darker, and where people need more vitamin D over UV protection, their skin is lighter. By using UV radiation as a factor in studies high frequencies of rickets disease, or the need for vitamin D in healthy pregnancies, it can be helpful to know who needs more vitamin D, or need to be in the sun less or more to be healthier.

 4.  The study of environmental influences on adaptations is a better way to understand human variation than by the use of race because race is a cultural and social characteristic.  The adaptations of solar radiation are better understood by studying the 4 facets of adaptation (short term, facultative, developmental and cultural).  As seen in the developmental adaptation melanin, skin color is the result of this adaptation. Different environmental clines and melanin makeup in individuals are what cause skin color. It is one of the many adaptations to deal with high levels of solar radiation. These adaptations are key to these major variations and changes in the appearance and makeup of humans. Environmental influences are what must be studied in order to learn about why there is variation among humans, especially skin color.  The variation of skin color shows that our bodies are influenced by many simple things that normally people would not think of like the sun or altitude. Race on the other hand is all cultural based and has little to nothing to do with skin color at all therefore it is easier to understand variation by looking how a population adapts to exposure of the sun by the pigmentation of the skin.