Human Variation & Race

Humanity is very shallow species from a genetic perspective, in that most variation in our species is only skin deep.  But this lack of genetic difference has granted us the ability to rapidly adapt to varying environmental conditions which has made it possible for us to survive in most regions of the world without to much discomforts.  Adaptability to specific environmental stresses like say from high levels of solar Radiation, varies from person to person and from population to population. So to increase success for the population and to avoid or prepare for future challenges and obstacles like say to avoid vitamin D deficiency that can cause the bone disease known as rickets from occurring due to lack of sunlight entering thru your skin, you could consume a diet rich in vitamins D to compensate, or move closer to the equator where Ultraviolet radiation is more present. These environmental stresses are the cause of what little variation we have thanks to our four forms of adaptation: short term, facultative, developmental and cultural. Or to put it in more simpler terms, you can tie solar radiation to the reason why we have different skin colors and "races". So lets review the four forms adaptations in relation to solar radiation in order to better explain how this is all connected to skin color andrace. 

• Facultative adaptation do not require a change in an organism’s DNA but they do involve turning on and off genes to alter a phenotypic expression in response to an environmental stress. This is the the case in vitamins D production the body as a certain amount of shortwave ultraviolet radiation (UVB) must penetrate the outer skin layer in order for the body to produce vitamin D. In far northern latitudes, solar radiation is relatively weak most of the year compared to the Equator, specialized cells called melanocytes that are located in the base of the epidermis, or outer skin layer, have photosensitive receptors that react to ultraviolet radiation and produce melanin within a few hours of exposure to regulate penetration.  In such an environment weresunlightis limited, very dark skin is a disadvantage because it can prevent people from producing enough vitamin D, which can lead to rickets disease in children, osteoporosis in adults, and women that suffered from a history of vitamin D deficiency in their childhood had a higher incidence of pelvic deformities that prevent normal delivery of babies such is the case for African Americans women (15% have pelvis deformities) when compared to European Americans(2%), however too much ultraviolet radiation penetrating the skin may cause the breakdown of folate in the body which can cause anemia, lower sperm cells production, higher risk of miscarriage, and neural tube defects in babies. This adjustment in the phenotype will remain for as long as the stress exists in various forms (variation in solar radiation based on location) , but the longer it takes the more natural selection comes into play and leads to the next adaptation 

• Developmental adaptations are are actual changes in the DNA of a population of individuals in response to a long-term stress to produce a phenotypic change through evolutionary forces. Such force is shown through the nature selection for darker skin in tropical latitudes, especially in non-forested regions, where ultraviolet radiation from the sun is usually the most intense. Melanin acts as a protective biological shield against ultraviolet radiation. Nature selects for less or lighter melanin when ultraviolet radiation is weak, in order for more production of vitamin D to continue despite the lack of the sunlight to trigger the melanocytes. Two forms of melanin are produced—pheomelanin which is red to yellow in color so light can pass more easily is more often produced by light skinned individuals whose ancestors travelled and settled north , and eumelanin which is dark brown to black which is difficult for light to pass through is more common with dark skinned individuals who's ancestry stayed at or near the equator. By doing this, it helps to prevent sunburn damage that could result in DNA changes but still have the flexibility too continue melanin production if access to solar radiation dwindles. They can potentially alter minimally during development depending upon the length of the environmental stress, but once established, that trait will be expressed for the life of that individual. However, just because the alterations were minimal and short doesn't mean it shouldn't be discussed. 

• Short-term adaptation occurs when traits allow an organism to respond quickly to changes in the environment to maintain homeostasis (i.e., normal physiological conditions). Ultraviolet radiation reaching the earth usually increases in summer and decreases in winter. The change in skin coloration is a seasonal acclimatization to the destructive effects of ultraviolet radiation from the sun. Tanning is primarily an increase in the number and size of melanin granules due to the stimulation of ultraviolet radiation. Tanning is often most noticeable on light complexioned people, however, even those with very dark brown skin can tan as a result of prolonged exposure to the sun. These temporary response to a temporary stress do not require genetic change however though they are certainly controlled by genes as is the case of Some Northwest Europeans who have substantially lost the ability to tan as a result of relaxed natural selection that created a defective form of a skin protein Mc1r (melanocortin-1 receptor) which is necessary for the production of melanin. With that said, if humanity was bounded by its genetic shortcomings we would not have a population that was as widespread as ours. That's were culture comes in.

• Cultural adaptation is the use of culture (tools, diet, social practices, reproductive behaviors, migratory patterns, clothing styles, and etc.) to help adapt to a given environmental stresses. The Inuit people of the American Subarctic for example, live in far northern latitudes but have darker skin pigmentation. This disadvantage in vitamin D production is Compensated by having a diet of eating fish and sea mammal blubber that are high in vitamin D. Similarly most developed nations now combat vitamin D deficiency by fortifying milk with vitamins D and A in order to prevent developmental problems as more of our modern lifestyle is driven indoors and away from the sun. Solar radiation adaptation in culture has also been shown in how radiation is blocked to some degree by hairstyles, clothing choices, smog/general pollution, drugs (sunscreen), and trees or other structures that were developed or used to provide shade. In fact, migratory patterns of early primates that left Africa may have been in search for easier environment to live in as Africa soon was drenched in solar radiation that altered the vegetation after the ice age.


The best way to use race to understand the adaptations to Ultraviolet radiation is that black and darker skinned people are better equipped to adapt to the sun then pale and white skinned people. A better explanation of the link between Ultraviolet radiation and skin pigmentation is that pigmentation is a product of evolution that was influenced by the locations of specific environmental stresses i.e. by how much sunlight they received ultimately decided who could or was favored to pass on their traits to the next generation which led to the variation of skin color we have today. You can even see the correlation between solar radiation and skin pigmentation by looking at the maps for Facultative and deveopmental adaptation that the more radiation in an area the more darker the local resident are likely to be. With a basic understanding of high levels of solar radiation, you can gather more background knowledge about human variation then you would just relying on the finished product of skin pigmentation.