Physiological and Cultural Adaptations to High Solar Radiation.

 I chose the environmental stress of “high levels of solar radiation” and its effects on those living in conditions of extreme exposure. Geographic locations affected by extreme solar radiation aren't necessarily limited to warm climates. Although extremely hot environments can be a sign of high solar radiation levels, high altitudes and atmospheric conditions with less cloud coverage, as well as constant exposure to the sun, can also be factors. The negative effects of living in these environments consist of electrolyte and water imbalances, which cause heat stroke and dehydration, leading to low levels of energy and, in more extreme cases, death. Organ functionality can be negatively impacted, as organs such as the heart and brain may fail to receive enough oxygen carried through the bloodstream due to the overexertion of energy used to cool the body and conserve water. Vitamin B9 (folate) can also be broken down in the bloodstream, which slows the building of red blood cells and the process of DNA synthesis, leading to birth defects in children as well as negative health effects in the mothers.  Humans living in these conditions would be a high risk for developing skin cancers such as melanoma and other damage to DNA and skin barriers as well if it were not for the type of melanin called eumelanin that is found in those of African descent and is darker compared to pheomelanin which is seen mostly in those with a lighter complexion. The eumelanin acts as a skin barrier for the UV rays caused by solar radiation, which otherwise would burn the epidermis as well as the dermis layer of the skin. 

(Long-term average of global solar radiation.)

As mentioned, there have been many adaptations to protect the physiological functionality of people living in high solar and UV radiation zones:

Short-term adaptations-Sweat Glands:

Short term adaptations found in those exposed to these extreme conditions consist of releasing perspiration from sweat glands to cool the external body temperature as well as the temporary thickening of the epidermis which can thicken within 4-5 days following exposure to high solar radiation, and can grow gradually thicker over weeks, but will revert to its original thickness after a month of less exposure and following the turnover of epidermis skin cells. Both of these adaptations can be of varying levels, in less extreme cases they exist within the environment of high solar and uv radiation but will dissipate once removed from this environment, however, like most effects of extreme climates, there are levels and too much exposure especially to non-natives to the climate may observe extreme sweating and sun poisoning, which is still temporary but should be looked into by a medical professional. 

Facultative adaptations- Vasodilation:

Vasodilation, where red blood cells will expand to release more blood flow closer to the surface of the skin, where the internal heat can be transferred externally through convection and radiation, also bringing cooler blood vessels into the body's bloodstream. This is a facultative adaptation because while the individual's DNA does not permanently alter to display this physical change, the temporary gene expression to control nitric oxide is activated, however it will revert to its normal homeostasis once removed from this condition after several weeks, no genes are permanently altered, only expressed differently in the conditions. 

Developmental adaptations-Limb structures:

An interesting developmental Adaptation to those living in parts of East Africa, specifically the Masai tribe, is seen in their long, slender limbs, which allow for greater surface area for heat dispersion and blood circulation. This is a trait seen in many places of high solar radiation, which is greatly concentrated in the African Continent. Longer arms and legs assist with losing body heat quickly in the high temperatures. This is a genetic trait which is still observed in parts of the Middle East as well as Africa, which are rather arid with low latitude, allowing for the penetration of more impactful solar radiation.

Cultural adaptations-Architectural Functionality:

The architectural style of the people of the Maasai tribe of East Africa conserves cool air by organizing the placement of housing to provide the most shade within villages, as well as constructing houses out of small rounded windows and use cow dung (this is very common and should not be written off as unsanitary), sticks and mud to thicken walls enough to preserve the coolair that enters the house in the evening. Culturally, every couple of months, those living in these communities will “replaster” their walls and floor with a fresh layer of mud and cow dung, which is cleaned and allows for proper insulation. Overhangs and windows on these homes and buildings allow for sun avoidance during the peak hottest hours of the day, facing away from the sun.

What are the benefits of studying human variation?

There are several benefits of studying the variation of the human species regarding their geographical location and the extreme climate conditions they endure. This includes learning what internal and external adaptations prevent illnesses and overexertion in these particular environments, such as overexposure to solar radiation. It is important to know what the causes of physical differences are and why some societies seem to thrive in particular environments more than others because, just as it is important for those with thick skin barriers to have adequate exposure to sun to absorb enough vitamin D (which otherwise would have to be supplemented with within the diet such as in polynesian cultures), it is important for those with weaker skin barriers and less melanin to protect themselves from the sun with spf or shade. 

Can race explain these adaptations?

While it is easy to assume that those within a race have a specific ancestral genetic lineage that relates to their personal set of adaptations, most of how they have adapted to their given climates, in any case of the extremes, is due to their location, not necessarily their race. The term “race” can be used to lump together people of a specific background; however, it has been seen on many occasions to be the case where differing “races” in neighboring regions of similar extreme climates have developed the same adaptations. An example of this would be the development of more surface area on the lips of a person having which ability an individual to cool faster in warm climates and climates of increased solar radiation. This is seen in people of African descent. Middle Eastern and Polynesian descent, all of whom experience high levels of sun exposure and have adapted genetically to form a similar (but not the same) facial feature. 

While these differing cultures of course have a very distant ancestor, their adaptations are analogous, making them the same through environmental factors, but not genetically predetermined factors. Environmental influences are a more reliable way in which to determine and understand the causes and effects that the climate and environment one lives in have shaped their internal and external facets. In this way, we can find the similarities in races without creating a subconscious division between them as all humans stem from a common ancestor, who, while their offspring evolved to their migrated-to environments, diverged only in ways that would give them their best shot at survival.