The stressor I chose was high levels of solar radiation. I think the growing prevalence of cancer, specifically skin cancer is probably why I chose this particular topic. It's our skin's ability or inability to catch up to the growing amount of solar radiation that we're being exposed to that negatively impacts the survival of humans. Primarily because those of us with ancestry that didn't require much protection initially, such as myself who is German and Danish (AKA northern European), has a very low to zero capability to create melanin in my skin as a response to the living closer to the equator as my ancestors. It's been reported that European Americans are 10x more likely to develop skin cancer than African Americans.
There are four ways humans adapt to this stressor. They are:
1) Short Term: I would say that our body's ability to create sweat in order to deal with the over-exposure to heat is one. It's our first reaction when exposed to higher temperatures than what our body is capable of dealing with.
2) Facultative: This happens through the skin creating more melanin in the epidermis when being exposed to sunlight. This is also known as "tanning". It's the body's way of creating a quick defense for the skin when being exposed to harmful UV rays. Even those with naturally dark skin will create more melanin to a certain level.
3) Developmental: This is very similar to "tanning" or the facultative adaptation, however this one spans through generations because it's a trait one is born with as opposed to one that happens as an immediate reaction and then dissipates. Unlike tanning that will go away or return the skin to a homeostatic state in a matter of days, the skin color change that occurs through many generations of humans living in a particular geographic region has long lasting effects. Those humans that live closer to the equator have significantly darker skin with more melanin that those who live closer to the north and south poles. The many variations of skin color throughout the human race are developmental adaptions to the amount of heat and sun exposure those areas have provided throughout the process of evolution.
4) Cultural: We have all adapted to the heat and amount of sun exposure through cultural practices. It ranges from our housing units, umbrellas (or anything that produces shade), using SPF when outdoors, wearing hats to protect our faces and even our clothing. (The picture I posted of the umbrellas is from Taiwan, and it was not a rainy day. Taiwanese women protect their skin from the harsh rays during the summer through the extensive use of umbrellas.)
It's easy to describe the adaptations described above in terms of race because it can be generalized that all Africans are dark-skinned, Asians are medium toned, and Europeans are all light skinned, but that's a very incorrect and gross generalization. Especially today when so many countries are multi-cultural.
I believe that understanding why we all have such various physical traits helps debunk the concept of "race" which is really nothing more than a sociological creation. There is a difference in the physical traits of one whose ancestors were native to India than one whose ancestors are from Korea yet they are both "Asians". Being able to break-down and understand how and why these physical adaptations manifested in the first place helps us better understand humanity as a whole. As we (humans) keep migrating throughout the world, these traits will continue to evolve and change through the years. I think that through our differences we obtain unity.
