Although beneficial in aiding the production of vitamin D
within humans, high levels of solar radiation negatively impacts the survival
of humans by disturbing homeostasis, or more specifically, damaging and/or
rapidly changing skin cells. This “damage” can begin as a sunburn, and has the
potential to be more destructive each time a sunburn occurs, and can result in
chronic hyperpigmentation, and even cancer
Humans have developed a short term adaptation to high solar
radiation-the reddening of the skin, in varying degrees up to and including sunburn
Another adaptation to solar radiation, of a more facultative nature, is tanning. When exposed in shorter lengths of time to solar radiation, melanin synthesis occurs, temporarily thickening a layer of the epidermis, and producing the appearance of darker skin in a localized area.
Humans who lived close to the equator, with the highest level of exposure to solar radiation, were found to adapt to this stress through the permanent darkening of skin's pigmentation. "High-UVR environments generated strong selective pressures on the skin and human body, leading to the evolution of permanently dark constitutive pigmentation, and the ability to increase eumelanin production in response to seasonal increases in UVB." http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3024016/
Lastly, several cultural adaptations have developed from this environmental stress...for example:
Sunscreen...
The benefit of studying human variation across various clines is that it removes prejudice or other possible stereotypes from the equation, leaving only objective results and expands our test group. It also allows us to see any potential benefits of this environmental stress, such as vitamin D increases due to exposure to solar radiation.
The use of race to understand human variation, especially related to the study of solar radiation, would just be a redundant restatement of the question. Skin color is simply a more concentrated pigmentation due to these environmental factors. These influences provide a static foundation for analysis across the variety of humans, instead of promoting a changing test group...much more accurate and objective.
I loved this statement: "The benefit of studying human variation across various clines is that it removes prejudice or other possible stereotypes from the equation..."
ReplyDeletePerfect. That is exactly correct and explains why using race won't work.
The rest of your post is excellent, with the one exception of your short term adaptation. Sun burns are actually a sign that your body is NOT adapting fast enough. It is a failure to adapt, not an adaptation in an of itself.
Loved the images, though the one of the skin peeling was unnerving!
Kristin,
ReplyDeleteThis was a very informative post. I never knew that when the skin thickens when tanning to produce a darker appearance. I agree that using race to try and understand human variation related to solar radiation would be redundant because the color of our skins are just concentrated pigmentation due to environmental stresses. Great post.
Great post Kristin! I personally have suffered the skin peeling and you can see how is the way of your body saying that it can stand that much sun. I agree with you on the fact that studying these responses from our body to the environment is the way to remove all kind of prejudice and it can be helpful to explain why we are not all the same. Love all the pictures.
ReplyDeleteI like your post. It is informative and well explained. It is amazing when you think about it how the human body adjusts to the solar radiation in the different ways such as reddening of the skin, and changing the colors of skin pigmentations permanently, as it did in areas where the sun is extremely hot.
ReplyDeleteIt is also interesting that the body needs a certain amount of sun rays to get what it needs as far as vitamin D, however, too much of it can be harmful and even cause cancer.