Lab6_Human_Skin_Color_Variation updated

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Lab 6: Human Skin Color Variation A close-up photograph of human skin Learning Objectives  Describe the cellular process that produces skin color.  Evaluate the hypothesis that human skin color tones differ in relation to levels of ultraviolet radiation exposure.  Describe the positive and negative selective factors that account for differences in human skin colors. Supplies Needed ● Internet access ● Worksheet (provided) Readings ● Rivera, Michael B.C. 2019.“Chapter 13: Race and Human Variation” In Explorations: An Open Invitation to Biological Anthropology, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff. Arlington, VA: American Anthropological Association. http://explorations.americananthro.org/ ● Fitzpatrick, Leslie E. 2019. Chapter 14: Human Variation: An Adaptive Significance Approach. In Explorations: An Open Invitation to Biological Anthropology, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff. Arlington, VA: American Anthropological Association. http://explorations.americananthro.org/ Modified from Explorations Lab and Activities Manual http://explorations.americananthro.org/

Introduction The purpose of this lab is to understand the cellular process that produces skin color and explore the evolution of skin color variation. By doing so, you will be able to question ideas about the alleged biological basis of race. In this activity, you watch two videos produced by Howard Hughes Medical Institute (HHMI) Biointeractive to learn about the biology of human skin color and the evolution of skin color variation. For Further Exploration ● American Anthropological Association. Understanding Race Project . ● Jablonski, Nina G. 2012. Living Color: The Biological and Social Meaning of Skin Color . Berkeley, CA: University of California Press. ● Jablonski, Nina G. 2004. “The Evolution of Human Skin and Skin Color.” Annual Review of Anthropology 33 (2004): 585–623. References Fitzpatrick, Leslie E. 2019. Chapter 14: Human Variation: An Adaptive Significance Approach. In Explorations: An Open Invitation to Biological Anthropology, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff. Arlington, VA: American Anthropological Association. http://explorations.americananthro.org/ Rivera, Michael B.C. 2019.“Chapter 13: Race and Human Variation” In Explorations: An Open Invitation to Biological Anthropology, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff. Arlington, VA: American Anthropological Association. http://explorations.americananthro.org/ HHMI Biointeractive. The Biology of Skin Color . Narrated by Nina Joblanski. Chevy Chase, MD, HHMI Biointeractive, 2020. Video, 18:58. HHMI Biointeractive. How we Get our Skin Color. Narrated by Nina Joblanski. Chevy Chase, MD, HHMI Biointeractive, 2015. Video, 3:32. Modified from Explorations Lab and Activities Manual http://explorations.americananthro.org/

Image Attributions Human skin close-up by Montavius Howard (TongCreator), from Pixabay is in the public domain. Human Skin Color Variation Worksheet Step One: Exploring the Biology of Skin Color and Understanding the Evolutionary Pressures of Skin Color Watch the two videos How We Get Our Skin Color and The Biology of Skin Color produced by HHMI BioInteractive. The first video describes how skin pigment is generated by skin cells as protection against ultraviolet (UV) radiation. The second film explores the hypothesis that different tones of skin color in humans arose as adaptations to the intensity of ultraviolet radiation in different parts of the world. After watching the videos, answer the following questions. 1. List the three layers of skin and indicate which layer of skin gives humans their skin color. Epidermis: the top layer, the layer with melanin producing skin colors. Dermis: the middle layer makes up most of the skin. Hypodermis: the bottom layer, fatty. 2. Briefly describe the functions of keratinoctyes and melanocytes. Keratinocytes and melanocytes are two types of cells found in the epidermis. Keratinocytes are the predominate cell in the epidermis, they produce keratin, a protein that creates structure and strength to hair skin and nails, keratinocytes build up the skins structure and protectiveness. Melanocytes are responsible for making melanin, the amount and type of melanin produced is what affects skin color. 3. Describe the cellular process that produces skin color. Be sure to include the following terms: malanosome, melanin, tyrosine, keratinocytes Tyrosine is converted into melanin through enzymatic reactions with tyrosinase, an enzyme that is crucial for melanin synthesis. Synthesized melanin is formed into structures called melanosomes within the melanocytes. Melanocytes go to surrounding epidermal cells primarily the keratinocytes in a a cellular process called melanosome transfer. Melanin within Modified from Explorations Lab and Activities Manual http://explorations.americananthro.org/

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keratinocytes provide protection from harmful effects of UV light from the sun. The amount and type of melanin transferred to keratinocytes is what produces variations in skin color. 4. How does melanin protect the cells from UV radiation? Melanin protects cells from UV radiation through a process known as photoprotection. melanin absorbs uv radiation from sunlight to prevent damage to skin cells. It takes the absorbed radiation and converts in into harmless heat. Melanin is distributed through the epidermis to ensure that radiation is intercepted before it can go deeper. Melanosomes that contain melanin are transferred from melanocytes to nearby keratinocytes. where it can shield the dna of keratinocytes from uv damage. 5. What are the risks of UV radiation? From exposure to ultraviolet light you may be prone to sunburn, premature aging, melanoma, cell carcinoma, as well cataracts. 6. Briefly state what determines an individual's baseline skin color and how much it can tan. The proportion of eumelanin to pheomelanin, the amount and type of melanin produced, and the number and size of melanosomes and how they are distributed. 7. What color skin (excluding hands, feet and face) do chimpanzees have under their fur? Chimpanzee skin color is generally white, the hands, feet and face are usually black. 8. What type of melanin do lightly pigmented people have? Lightly pigmented people typically have a higher proportion of pheomelanin compared to eumelanin. 9. What type of melanin do more darkly pigmented people have? Darkly pigmented people typically have higher levels of eumelanin compared to pheomelanin. 10. What other body parts does melanin color? What does melanin do for other species? It can affect hair color and eye color. For other species it can affect the color of feathers and fur to aid in camouflage. 11. What kind of raw data helped Dr. Nina Jablonski find the answer to her questions about the relationship between UV radiation and human skin pigmentation? UV measurements of the earth’s surface by NASA. 12. In general terms, how is UV radiation intensity distributed throughout the world? UV radiation is most intense near the earth’s equator as well as high altitudes. 13. How do scientists measure skin color? Scientists measure skin color using a Reflectometer. 14. Why are folate and vitamin D important nutrients? Folate is essential for producing red and white blood cells in bone marrow, producing DNA and RNA, and transforming carbohydrates into energy. Vitamin D helps regulate the amount of calcium and phosphate in the body. 15. Describe the selective pressures for the production of darkly pigmented skin in areas with high UV radiation intensity. Modified from Explorations Lab and Activities Manual http://explorations.americananthro.org/

Increased amounts of melanin protects the nucleus from accumulated mutations due to high UV radiation intensity. 16. Describe the selective pressures for the production of lightly pigmented skin in areas with low UV radiation intensity. With low UV radiation intensity having lighter skin allows for more UV to reach the skin. The sun's ultraviolet B interacts with a protein called 7-DHC in the skin converting it into a vitamin D. 17. Describe the evolutionary interplay between folate and vitamin D. Melanin pigmentation and the evolution of dark skin is an adaptive protective mechanism against high levels of UVR exposure. Skin pigmentation balances folate preservation and Vitamin D production. Both micronutrients are essential for reproductive success. 18. What do scientists infer from the lack of variation in the MC1R gene among African populations? They infer that the MC1R gene changes the color of skin darker and more UV causes more MC1R. 19. Why are light skinned people at greater risk for skin cancer than dark skinned people? Black people are far less likely to develop melanoma due to the protection that melanin, the body's natural skin pigment, provides from damaging ultraviolet rays . 20. Why might dark skinned people living in high latitude environments need to take a vitamin D supplement? (Note: please always consult your doctor before starting any supplement regimen). Dark skinned people in higher latitude environments may not be able to absorb enough UVB and therefore have lower levels of Vitamin D. Step Two: Bringing it all Together: Racism and Skin Color Read the following statement about race and racism from the American Association of Physical (Biological) Anthropology. Next, read the following news article from Voice of America about skin color and racism and discrimination on a global level. Then, complete the following writing task: As you have learned in your study of human variation, most human traits, including skin color, are non-concordant. That is, skin color is inherited independently of other genetically controlled traits. Imagine that you are talking with a friend who knows very little about this topic. In two paragraphs, summarize in your own words what you have learned in this activity. Explain to your friend how skin color is one piece of evidence for the biological fallacy of race. Describe to them how skin pigment is produced and why it varies between people throughout the world. Discuss with your friend the dangers of when people believe that race is a real and legitimate way to categorize people and that phenotypical differences such as skin color are related to something deeper in one’s biology. Share your thoughts about the role of education to fight the social construction of race that has disproportionately disadvantaged people with darker skin tones and provided unearned advantages for those with light skin tones. Modified from Explorations Lab and Activities Manual http://explorations.americananthro.org/

Skin pigment is produced using the synthesis of melanin, the pigment responsible for skin, hair and eye color. Melanin comes in two types, eumelanin which ranges from brown to black, and pheomelanin, which ranges from red to yellow. Darker individuals tend to have more eumelanin, while lighter skinned individuals have higher levels of pheomelanin. You experience difference skin colors across the world due to the adaptation to different UV radiation levels in various regions. It is important to understand that using skin color or other external features for racial categorization is wrong. We all have the same skin, made up of the same types of cells. The only thing that differs between some is color. Believing in race as manmade concept can lead to racism such as discrimination or creating false stereotypes. Modern day education plays a major role by trying to recognize the social aspect behind race and is working to get rid of prejudiced beliefs. Modified from Explorations Lab and Activities Manual http://explorations.americananthro.org/

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Lab6_Human_Skin_Color_Variation updated

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