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Variation in Human Skin Color

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❶The red color 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. Melanin is responsible for the color of our eyes.

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Melanins, the pigments that color our eyes, hair and skin
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Assign to each group one of the skin-variation resources below to read and report on to the rest of the class. Students should use their Variation in Human Skin Color student esheet to go to their assigned resource. Have each group answer the corresponding questions on their Resource Questionnaire handouts. Explain that it will be their job to teach the class what they have learned about skin variation from their assigned resource, using their answers to the questions as a framework.

Resource presentations should be done in chronological order. When the groups have finished their presentations, the class as a whole should review and discuss what they have learned. Students need to recognize that skin color is an alterable characteristic that results from adaptation in a specific environment that has survival value for the organism and may then be perpetuated by the process of natural selection.

Focusing on the biological similarity that underlies skin-color variations should equip students to critically evaluate the improper use of differences in skin color to divide humans into distinct races. To help students integrate what they have learned and recognize the social implications of skin color, have them answer this question in a journal entry:.

Divide the class into pairs. Have each pair discuss their journal entries and create a poster informing the public about what determines skin color and how we should treat other people individually and as a society based on this knowledge. Have the pairs explain their posters to the class and display them on the bulletin board.

Students may appreciate reading an article in Science magazine, Zebrafish Researchers Hook Gene to Human Skin Color , about how an international team of researchers were able to identify a zebrafish pigmentation gene and its human counterpart, which is thought to account for a significant part of the difference between African and European skin color.

It is a graphic presentation of biological findings rooted in genetics research that includes striking displays of phenotypic variations and evidence on human migrations and adaptations, while showing how erroneous conventional wisdom has been with respect to the deeply ingrained concept of discrete "races. Students can learn more about the science, social, and historical aspects of race and how people are classified by visiting the online companion to the popular PBS documentary series, Race: The Power of an Illusion.

Students may enjoy learning about human evolution by visiting the Becoming Human website. The site content includes a broadband documentary organized by evidence, anatomy, lineages, and culture , related educational interactivities, lesson plans, resources, and current news and features. Ideas in this lesson are also related to concepts found in these health education standards: Health Education Standard 2: Students will analyze the influence of family, peers, culture, media, technology, and other factors on health behaviors.

Funder Info This content was created with support from Neutrogena. Because people with red hair are less able to make the dark eumelanin pigment, their skin is generally quite pale and burns easily with sun exposure. Although people with dark hair may still produce the yellow-orange pheomelanin, it is largely masked by the dark eumelanin pigment and cannot easily be seen.

However, the red-yellow pheomelanin is believed to cause the warm, golden, or auburn tones found in some types of brown hair.

The range of colors produced by melanins is limited to shades of yellow, brown, red, and black. Grey hairs contain only a few melanin granules, spread out through the hair. White hairs contain no melanin at all: Often you find either eumelanin or pheomelanin in hair, but not both.

Adjacent patches of hair follicles may show a very precise split between the two pigment types. This effect is most obvious in the patterns and markings of other mammals, such as leopards, tigers, and certain breeds of dog. Low levels of pheomelanin in the absence of eulamelanin are characteristic of cream-colored hair in many animals. Pigments are discussed in more detail in the pages on blue eyes and green plants.

Melanin reduces ultraviolet induced DNA damage by absorbing or scattering the ultraviolet radiation that otherwise would have been absorbed by the DNA. This prevents the development of melanoma, a potentially deadly form of skin cancer, as well as other health problems related to exposure to strong solar radiation. The amount of UV radiation that is absorbed or scattered is determined by a number of factors: Skin color depends upon the size, number, shape, and distribution of melanosomes, as well as the chemical nature level of activity of their melanin content.

There are 6 different skin types that are defined by dermatologists. Skin type Description Type 1 Always burns, never tans. Very fair skin with red or blond hair and freckles. Type 2 Burns easily, tans minimally. Type 3 Sometimes burns, gradually tans. Type 4 Minimum burning, always tans. White, with medium pigmentation.

Type 5 Seldom burns, always tans. Medium to heavy pigmentation. Type 6 Never burns, but tans very darkly. African Americans, Africans, or dark-skinned individuals with heavy pigmentation. The darkest skin tones are found in tropical latitudes with open grassland, while areas further from the equator that are forested tend to favor lighter skin tones.

There is a striking correlation between geographic conditions, particularly exposure to sunlight, and skin tone. These differences have evolved to find the balance between the benefits and the dangers of the ultraviolet UV radiation we absorb from the sun.

Early humankind living in the sun-soaked savannah plains of Africa developed a dark-toned skin, rich in the pigment melanin. Within the skin cells, melanin concentrates above the nucleus, shielding the vital DNA from radiation damage. In an environment where there is little to break the path of sunlight onto the skin, this barrier is a great advantage.

There are other benefits to having a high concentration of melanin in the skin and other parts of the body. Darker-skinned individuals also age better, as their skin is better protected from sun damage. It is the UV component of sunlight that helps the body utilize vitamin D.

This vitamin helps promote bone growth, maintaining the right balance between calcium and phosphorus in the body. A deficiency of vitamin D leads to rickets and similar diseases. It seems that, as early peoples migrated away from the equator into areas less exposed to the sun, there was not enough UV radiation to produce sufficient vitamin D to prevent diseases such as rickets.

Their bodies compensated by producing less melanin, so that more sunlight would be allowed through. They could then produce sufficient vitamin D with less exposure to sunlight. Light-skinned people visiting sunny locations may not have enough melanin to block the sun sufficiently, and may burn their skin without the protection of sunblock. Yet when a certain amount of UV rays penetrates the skin, it helps the human body use vitamin D to absorb the calcium necessary for strong bones.

This delicate balancing act explains why the peoples that migrated to colder geographic zones with less sunlight developed lighter skin color. As people moved to areas farther from the equator with lower UV levels, natural selection favored lighter skin which allowed UV rays to penetrate and produce essential vitamin D. The darker skin of peoples who lived closer to the equator was important in preventing folate deficiency. Measures of skin reflectance, a way to quantify skin color by measuring the amount of light it reflects, in people around the world support this idea.

While UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.

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Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skinned humans. The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the .

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Skin color is one of the most visible indicators that helps distinguish human appearance, and a new study provides more detail as to how one protein helps produce this wide palette.

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Modern Human Diversity - Skin Color Why do people from the tropics generally have darker skin color than those who live in colder climates? Variations in human skin color are adaptive traits that correlate closely with geography and the sun’s ultraviolet (UV) radiation. Our skin color is determined by a pigment called melanin, and while everyone has melanin (both fair and dark-skinned people), it comes in different forms and ratios. The two forms of melanin are called eumelanin and pheomelanin.

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A page from the "Causes of Color" exhibit Melanins, the pigments that color our eyes, hair and skin Human beings come in a glorious spectrum of different colors: light, dark, plain or freckly skin; black, brunette, blond, auburn, and white hair; and eyes that are blue, hazel, green, amber and brown, to . What Determines Skin Color? In the human body, everything that is controlled by proteins is controlled by genes, since it is the genes which encode the proteins. This case applies for melanin as well. There are two ways in which skin color can be affected by genetics. One, if the genes responsible for formation of an enzyme known as.