Solar radiation can have positive and negative effects on the climate, ecosystem and living organisms on earth. Solar radiation which presents through the visible light helps us see clearly during the day time, and the infrared solar radiation or infrared light provides us heat. Ultraviolet radiation, also known as black light, is a source used for medical equipment sterilization and natural skin tanning. These are the more common positive effects that we get from the sun's radiation. Overexposure to the sun's rays leads to life threatening conditions, such as skin cancer. Too much UV radiation may cause skin cancer and alter your immune system, and make you vulnerable to infectious diseases. It may also cause a person to have cataracts and other eye diseases, and excessive infrared radiation may lead to heat stroke. High levels of solar radiation also impacts the survival of humans by disturbing homeostasis. UVA rays are more dangerous to humans as they have the ability to penetrate through the epidermis (top layer of skin) to the dermis (second layer of skin). UVB rays only have the ability to penetrate the epidermis layer. There is one benefit humans receive from UV radiation and that is the production of vitamin D from UVB rays. If humans get sunburned the UVA and UVB rays can cause the immune system to be suppressed for a short time. UVB rays are the most harmful towards humans, because it can damage our DNA cells and potentially cause genetic problems, and lead to skin cancer. This type of damage can disturb homeostasis and can be life threatening to the human species.

Short term adaption does not pertain to high levels of solar radiation. If a person becomes overexposed to UVA and UVB rays they could become sunburned. If a person has a sunburn then this is a sign that the human has failed to adapt to the high level of radiation. A sunburn simply lets us know we have been overexposed, and can be dangerous as mentioned before. A fair skin person is more likely to get a sunburn when compared to a person of darker skin. A person with high skin pigmentation also known as melanin is less likely to a get sunburn, because melanin helps to protect us from UV rays. Fair skin people do not produce as much melanin causing them to burn easier and may have to use other products to help avoid sunburn. 

A type of facultative adaptation that helps to protect our skin from the harmful UV rays would be tanning. Tanning occurs when exposure to sunlight triggers a protective mechanism through increased melanin on the epidermis layer. Melanin can also act as a natural sunscreen produced by our bodies, and the epidermis layer will remain tanned until no longer being overexposed to UV rays. When people spend more time in the sun during the summer season, it is common to see fair skin people and dark skin people have a darker pigmentation. People who are albino have a genetic mutation preventing their bodies from producing melanin. When people lack the ability to tan they are more likely unable to protect their skin from UV rays. 

A developmental change can be found in populations which have a higher amount of people with darker skin pigmentation. People with darker skin pigmentation again, have higher melanin levels which acts as a natural sunscreen protecting our skin. Populations that have the most exposure to the sun's harmful rays for example, can be in parts of Africa such as the Savannah or plains. There seems to be a direct correlation geographically in those regions that shows a higher density of people with darker skin pigmentation. Too much exposure to UV rays can result in skin cancer, but if there isn't enough exposure a person can become vitamin D deficient which can have negative effects on the body. Populations that lack sun exposure can be prone to developing diseases such as rickets. Populations with lighter skin pigmentation do not produce as much melanin which can be due to less sunlight. 

A cultural adaptation to the harmful UV rays is clothing, shelter and sunscreen lotions. The invention of shelter and clothing made it possible for early homo sapiens to avoid high levels of melanin production. Migration to other environments also contributed to the reduction of high levels of UV exposure. Geographically we can see that populations with lighter skin are in northern regions and populations with darker skin pigmentation are in the southern and central regions near the equator. People that take part in outdoor activities or  play sports are also at risk for high levels of UV ray exposure. The invention of sun screen helps people in certain regions to protect their skin from UV ray exposure. However, it is not considered a solution that completely protects you from skin cancer regardless if you are a dark or light skinned person. 

The benefits of studying human variation is that by studying the changes within a population we can evaluate and see the environmental stressors that can affect that population. We can take a population with certain traits and move them to a new environment other than were they currently live, and eventually we will see an evolutionary adaptation to the new environment. For example, studying rickets in fair skinned populations can help us understand how we need some sunlight exposure in order to avoid the disease. The study might help scientist come up with a solution for populations at risk for rickets in certain regions whether it is a lack of just vitamin D or a lack of sunlight or both, they would be able to narrow it down.

The only time race should be used is when classifying geographic populations of people that have  a similar set of adaptations to an environment. This will allow us to see how our ancestors developed and changed over time, and we can have a better understanding of the origins of that population. I think we will also see what type of changes might occur in that population given the different type of environmental stressors. For example, if we had moved a group of light skin people to Africa in the Savannah, we could see how well the group will adapt compared to dark skin populations that already populate the area. Scientists could see more people with sunburn and higher levels of melanin, and we would see a change in skin color in the group of lighter skin people. I think by studying the environmental influences of a population overtime, there will be changes that occur as the group adapts to those stressors. Some adaptations can become permanent and others can remain until the stressor is removed. For example, being born light or dark skin can be permanent, and people that tan in the sun during summer will remain darker until the increased sun exposure is removed or lessened. The ability to adapt to a new environment has been passed down from previous generations, and connects humans more closely on a genetic level compared to any of the outward differences we may see. By studying the human species we can use this as a tool to help people overcome racism, and help people see how we are in many ways very similar and less different from each other.