White people (also Caucasian) is a term which usually refers to human beings characterized, at least in part, by the light pigmentation of their skin. Rather than a straightforward description of skin color, the term white denotes a social status and functions as a color metaphor for race.
One common definition of a "white person" is a person of primarily European ancestry.[1] However, the definition of a "white person" differs according to geographical and historical context, and various social constructions of whiteness have had implications in terms of national identity, consanguinity, public policy, religion, population statistics, racial segregation, affirmative action, eugenics, racial marginalization and racial quotas. The concept has been applied with varying degrees of formality and internal consistency in disciplines including: sociology, politics, genetics, biology, medicine, biomedicine, language, culture, and law.
White skin
White people are archetypically distinguished by light skin. Europeans have lighter skin (as measured by population average skin reflectance read by spectrophotometer at A685) than any other group that was measured. Southern Europeans (measures taken from Spaniards) show a skin pigmentation in parts of the body not exposed to the sun similar to that of Northern Europeans and, in some cases, even lighter.[26] While all mean values of skin reflectance of non-European populations are lower than Europeans for the groups represented in this study, there is significant overlap between populations.[27] This observation has been noted by the Supreme Court of the United States, which stated in a 1923 lawsuit over whiteness that the "swarthy brunette[s] ... are darker than some of the lighter hued persons of the brown or yellow races".[28] The epidermis of light skinned people is not white nor free of pigment. The underlying layers of collagen and adipose tissue are white in people of all races. In lightly pigmented people, the epidermis is an almost transparent layer of film. Consequently the epidermis allows the underlying white tissues to become visible.[29] Blood vessels interlaced between the adipose tissue produce the pale pink color associated with light skin. Pigments known as carotenes found in the fat produce a more yellow effect. In darker skinned people the epidermis is filled with melanosomes that obscure the underlying layers.[30][31][32]
Origins of light skin
The main hypotheses which attempt to account for white skin suggest it is an adaptation to inadequate ultraviolet radiation. As humans moved out of the tropics, a conspicuous latitude gradient of skin tones follows the out of Africa dispersion, it is argued natural selection for sufficient ultraviolet penetration to enable vitamin D production gave rise to the evolution of skin pigmentation by the mechanism of evolution by natural selection. Deleterious health effects of insufficient vitamin D are also pointed to as confirmation that skin lightening was in response to strong selection pressure for maximizing vitamin D.[33][34][35] A variation of the vitamin D argument is that humans lived in Europe for several thousand years without their skin lightening and that it only became white after they adopted agriculture.[33][36] It is suggested that in Europe the latitude permitted enough synthesis of vitamin D combined with hunting for health, only when agriculture was adopted was there a need for lighter skin to maximize the synthesis of vitamin D , therefore it is suggested the elimination of game meat, fish, and some plants from the diet resulted in skin turning white several thousand years after modern human settlement in Europe.[37][38]
A 2006 study concluded that light pigmentation in Europeans is at least partially due to the effects of positive directional and/or sexual selection.[39] According to Luigi Luca Cavalli-Sforza, light skin probably arose in North Africa or both in the north and east.[40] Skin color is a quantitative trait that varies continuously on a gradient from dark to light, as it is a polygenic trait, under the influence of several genes. Many of these genes have yet to be identified. However, two genes that are known to contribute to skin color are MC1R and SLC24A5. The mutation resulting in the light skin version of the SLC24A5 gene has been estimated to have originated in Europe between 6,000 and 12,000 years ago, indicating that at least one of the genes responsible for pale skin colour in Europeans arose relatively recently.[41]
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