Human Variation

Solar radiation impacts the survival of humans if the level of exposure is too high or too low.  Of course, solar radiation is needed as a source of Vitamin D. Having inadequate amounts of Vitamin D can contribute to weakened protection from UV rays, high blood pressure, and developmental factors such as skeletal deformities. Overexposure of UV radiation can cause damage to the DNA. UV radiation is directly absorbed into the cells by the DNA which can cause skin cancer.  Also, UV radiation depletes folate - a B vitamin - which can disturb developmental processes in pregnant women and result in the defect spina bifida.  This damage at the genetic level disturbs homeostasis and is life threatening to the species.

   

Unfortunately, humans do not have a short term adaptation to over exposure to solar radiation.  However, humans have adapted to higher levels of solar radiation in many ways, and there are many factors of the adaptation.

A facultative adaptation humans have adapted to combat excessive solar radiation is by tanning, and temporarily producing more melanin.  

A developmental adaptation that protects humans from UV radiation is skin color.  Melanin is one of three factors that alter skin color and assists with protection from UV exposure by absorbing the UV radiation that causes genetic mutations.  Individuals that have had a greater exposure to solar radiation would tend to have a darker complexion due to increased melanin production.  Whereas individuals located in areas where they have less exposure to UV radiation, or limited exposure due to other conditions (more clothing due to colder climates), would have a lesser amount or lack of melanin, resulting in a lighter or fairer skin tone. 

Cultural adaptations to high levels of UV radiation can be the use of shelter and shade, clothing, and of course the use of sun screen. Sun screen is a modern tool used to provide supplementary protection from the sun.  Although, sunscreen isn’t complete protection, it does allow for longer UV exposure without damage.   

The benefit of studying across environmental clines is to see how different people have adapted to different environmental influences. If we only studied one environment, we wouldn’t see the whole spectrum of solar radiations impact.  By studying the effects of UV radiation on varying populations we understand how much radiation is necessary and how much is harmful for differently pigmented skins.  This information is useful for preserving health and can be used to preemptively avoid harm, such as sunburns, cancer, or folate deficiency.

As we learned in the lessons this week, there is no real race (other than the human race), so we have to look at the adaptations of those in a given environment.  In terms of solar radiation, this is the measurement of pigment in an individual’s skin.  Therefore, if you must use the term race, it would be defined as a population with similar adapted traits (in this case level of skin pigmentation).
Using the study of adaptations to environmental influences is a better way to understand human variation, because as we have learned, adaptation to environmental influences and mutation are the causes of the variation.