Variability in Skin Tone
Human skin shows high skin colour variety from the darkest brown to the lightest pinkish-white hues. Human skin shows higher variation in colour than any other single mammalian species and is the result of natural selection. Skin pigmentation in humans evolved to primarily regulate the amount of ultraviolet radiation (UVR) penetrating the skin, controlling its biochemical effects.
The actual skin colour of different humans is affected by many substances, although the single most important substance determining human skin colour is the pigment melanin. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin colour of darker-skinned humans. The skin colour of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the haemoglobin circulating in the veins of the dermis. The red colour underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or the stimulation of the nervous system (anger, fear), arterioles dilate.
There is a correlation between the geographic distribution of UV radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Areas that highlight higher amounts of UVR reflect darker-skinned populations, generally located nearer towards the equator. Areas that are far from the tropics and closer to the poles have lower concentration of UVR, which is reflected in lighter-skinned populations.
In the same population it has been observed that adult human females are considerably lighter in skin pigmentation that the males. Females need more calcium during pregnancy and lactation. Vitamin D which is synthesized from sunlight helps absorbing calcium. Females evolved to have lighter skin in order to help their bodies absorb more calcium.
| Description | ||
|---|---|---|
| I | Always burns, never tans | Pale, Fair, Freckles |
| II | Usually burns, sometimes tans | Fair |
| III | May burn, usually tans | Light Brown |
| IV | Rarely burns, always tans | Olive brown |
| V | Moderate constitutional pigmentation | Brown |
| VI | Marked constitutional pigmentation | Black |
Read more about this topic: Human Skin
Famous quotes containing the words variability in, variability, skin and/or tone:
“The grand points in human nature are the same to-day they were a thousand years ago. The only variability in them is in expression, not in feature.”
—Herman Melville (1819–1891)
“The grand points in human nature are the same to-day they were a thousand years ago. The only variability in them is in expression, not in feature.”
—Herman Melville (1819–1891)
“Smooth white skin invites something that will leave a trace, a kiss or a slap.”
—Mason Cooley (b. 1927)
“Our medieval historians who prefer to rely as much as possible on official documents because the chronicles are unreliable, fall thereby into an occasionally dangerous error. The documents tell us little about the difference in tone which separates us from those times; they let us forget the fervent pathos of medieval life.”
—Johan Huizinga (1872–1945)