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Which of the following statements about melanin is most accurate?
Melanin is not unique to humans. Many animals have melanin in their skin and hair; and, in fact, even bacteria produce melanin. Try again.
There are two primary types of melanin, eumelanin (brown-black pigment) and pheomelanin (reddish-yellow pigment). Both the type and amount vary from person to person. Try again.
Correct! The brown-black eumelanin absorbs sunlight, so the more a person has, the less sunlight is reflected and the darker their skin. Select another correct answer. You selected all the correct answers.
The brown-black eumelanin absorbs UV radiation, preventing it from damaging the cell’s DNA. This makes mutations in DNA less likely. Try again.
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Which of the following statements are true concerning how light interacts with the pigments in a red tomato?
Correct! Because we see the color red in the tomato, the pigments must absorb blue light. Select another correct answer. You selected all the correct answers.
In order for us to see red light, it must be reflected from the object we are viewing. The tomato is red, so red light must be reflected, not absorbed. Try again.
No evidence is provided that suggests that the pigments in the tomatoes can absorb UV light which can damage DNA. Seeing a tomato as red shows that the colors violet, blue, and green in the visible spectrum are absorbed. The energy level of light in the visible spectrum is too low to damage DNA. Try again.
Because the tomatoes appear red, red light must be reflected and other colors in the visible spectrum like green must be absorbed. Try again.
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In which of the following areas of the globe would you expect to find relatively high amounts of UV radiation? Select all that apply.
Persistent cloud cover blocks UV radiation, as described in the film for the Congo Basin. Try again.
Correct! Areas at high elevation like the Andes or Tibetan plateau have higher levels of UV radiation. Select another correct answer. You selected all the correct answers.
Correct! Areas at latitudes near the equator have higher levels of UV radiation. Select another correct answer. You selected all the correct answers.
Patterns of UV radiation are associated with latitude (north-south direction), not longitude (east-west direction). Try again.
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Which of the following statements apply to the variation in human skin color? Select all that apply.
Chimpanzee skin is mostly pale under their dark hair and does not exhibit the same range of color variation as human skin. Try again.
Correct! Melanin absorbs some wavelengths of visible light and reflects others. Different types and amounts of melanin affect the wavelengths of light absorbed and therefore reflected. Reflected light gives objects their color. Select another correct answer. You selected all the correct answers.
In the film we see that reflectometers can be used to quantify the color of a person’s skin. Dr. Jablonski compiled skin pigment data from field measurements made by anthropologists around the world. Try again.
Correct! Wherever UV is more intense, skin color tends to be dark. Where UV intensity is lower, skin is almost always lightly colored. Select another correct answer. You selected all the correct answers.
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Darker skin is more prevalent in high-UV areas. Dr. Jablonski proposed a hypothesis to explain the selective pressure for darker skin in these environments. On what evidence did she base this hypothesis?
It is true that there is little variation in the MC1R gene among people of African descent, suggesting that there is selection against different variants of this gene. But that fact does not directly help to determine what the selective pressure is for darker skin. Try again.
This statement is not correct and is not one of the observations on which Dr. Jablonski based her hypothesis. Try again.
Correct! This observation led Dr. Jablonski to propose that the ability to maintain high levels of circulating folate, a nutrient important for human reproduction, would provide a selective advantage to individuals living in a high-UV environment and favor individuals with larger amounts of eumelanin. Select another correct answer. You selected all the correct answers.
Although this statement is accurate, the average age of skin cancer diagnosis is well past a person's peak reproductive age. Dr. Jablonski reasoned that to be acted on by natural selection, a trait has to affect fitness: the successful production of offspring. Thus, she concluded that protection from cancer could not explain the selective pressure for darker skin. Try again.
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Human populations in low-UV environments tend to have lighter skin tones. One explanation is that the selective pressure for dark skin decreases as UV intensity decreases. At the same time, there is selection for lighter skin to absorb more UV radiation, which is needed for vitamin D production. What evidence supports the vitamin D hypothesis for the evolution of lighter skin tones?
In general, people with dark skin living in areas with low amounts of UV are at highest risk for vitamin D deficiency. Melanin provides a shield that keeps UV radiation from penetrating the skin. Try again.
This is true, but it does not explain the selective pressure at work. Try again.
Correct! In populations that get ample vitamin D from their diets, selection pressure for lighter skin would likely be lower. This observation supports the idea that the need for vitamin D production provided the selective pressure for the evolution of lighter skin. Select another correct answer. You selected all the correct answers.
The opposite is true. Darkly pigmented skin results in less efficient synthesis of vitamin D and very low production of vitamin D in low-UV environments, likely resulting in selection for lighter skin tones in these environments. People with lighter skin are more likely to get enough UV to synthesize adequate amounts of vitamin D in a wider range of environments. Try again.
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Based on the risk factors discussed in the film, which of the following groups should consider taking vitamin D supplements to avoid rickets?
Although dark skin prevents UV from being absorbed and starting the process of vitamin D synthesis in the skin, UV is so intense near the equator that even people with dark skin are not at great risk for rickets as long as they spend time outdoors. Try again.
UV radiation is most intense at the equator, so people living near the equator would not be at risk of vitamin D deficiency or rickets. Try again.
Although UV is less intense farther away from the equator, light skin absorbs more of it than does dark skin, putting people with lighter skin at less risk for vitamin D deficiency. Also, rickets is a disease that affects children and not adults, though vitamin D deficiencies have other consequences for adults. Try again.
Correct! Children born to parents with dark skin would likely have dark skin. Dark skin coupled with low UV intensity during winter months can limit vitamin D synthesis in the skin and lead to vitamin D deficiencies. In children, vitamin D deficiency can cause rickets. Select another correct answer. You selected all the correct answers.
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In what way does natural selection depend on the specific environment in which an organism lives?
An organism cannot purposely evolve in a needed direction. Evolution takes many generations and acts on existing variation in a population. Try again.
Correct! As an example, light skin is not beneficial in areas with high UV but was an advantage in areas with low UV. Select another correct answer. You selected all the correct answers.
Whether a trait is beneficial, harmful, or neutral depends on the environment. Darker skin is beneficial in a high-UV environment and lighter skin in a low-UV environment. Try again.
The origin of variation in a population is random as it depends on mutations occurring. However, the process of natural selection itself is not random. Inherited traits that help individuals survive become more common in a population. Sometimes there are strong selective pressures on a population, and biologists can make reasonable predictions about which traits will become more common. Try again.