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A. Melanin is found only in human cells and is not present in other organisms.
Melanin is not unique to humans. Many animals have melanin in their skin, hair, or feathers. Even some bacteria produce melanin. Try again.
B. Human skin cells contain only one type of melanin.
There are two main types of melanin in human skin cells: eumelanin, a brown-black pigment, and pheomelanin, a reddish-yellow pigment. The amounts of each type vary from person to person. Try again.
C. The more eumelanin an individual has in their skin cells, the darker their skin.
Correct! The brown-black pigment eumelanin absorbs sunlight. The more eumelanin a person has in their skin cells, the less sunlight is reflected by their skin, and the darker their skin appears. Select another correct answer. You selected all the correct answers.
D. The darker an individual’s skin color, the more likely ultraviolet (UV) radiation will damage the DNA in their cells.
Individuals with darker skin have more of the brown-black pigment eumelanin in their skin cells. This pigment absorbs UV radiation, which makes it less likely that the cells’ DNA will be damaged. Try again.
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A. The pigments reflect red light and absorb blue and green light.
Correct! The reason we see a tomato as red is because its pigments reflect red light. The tomato’s pigments also absorb blue and green light, which is why we don’t see the tomato as blue or green. Select another correct answer. You selected all the correct answers.
B. The pigments absorb red light and reflect blue and green light.
In order for us to see a tomato as red, its pigments must reflect red light, not absorb it. The tomato’s pigments must also absorb blue and green light, or else we would see the tomato as blue or green. Try again.
C. The pigments will protect DNA in the tomato’s cells from damage caused by UV light.
The film does not discuss the types of pigments in tomato cells and whether they can protect DNA from UV light. Try again.
D. The tomato fruit has the same types and amounts of pigments as in the plant’s leaves, stem, and roots.
The tomato fruit is red, so it must have pigments that reflect red light and absorb other colors. The plant’s leaves, stems, and roots are not red, so they probably contain more pigments that absorb red light and reflect other colors. Try again.
A. an area at a low altitude that is usually cloudy
Persistent cloud cover blocks UV radiation, and areas at lower altitudes also have lower UV levels. So, this area would likely have a low amount of UV radiation. Try again.
B. an area at a high altitude near the equator
Correct! Areas at higher altitudes, such as the Andes or Tibetan Plateau, have higher levels of UV radiation, as do areas at latitudes near the equator. So, this area would likely have a high amount of UV radiation. Select another correct answer. You selected all the correct answers.
C. an area near the ocean or other large body of water
The map in the film does not show a correlation between large bodies of water and levels of UV radiation. So, it is unclear whether this area would have a high or low amount of UV radiation. Try again.
D. an area at a longitude in the Western Hemisphere
The film shows that UV radiation varies with latitude (in a north-south direction), not longitude (in an east-west direction). So, it is unclear whether this area would have a high or low amount of UV radiation. Try again.
A. Data support a correlation between UV intensity and skin color variation.
Correct! This correlation has been shown using data on UV radiation collected by the National Aeronautics and Space Administration (NASA) and data on skin colors measured by anthropologists. Select another correct answer. You selected all the correct answers.
B. Human skin color variation is mostly determined by the types and amounts of melanin present in the skin.
Correct! There are two main types of melanin in human skin cells: eumelanin, a brown-black pigment, and pheomelanin, a reddish-yellow pigment. The amounts of each type in the skin determine skin color. Select another correct answer. You selected all the correct answers.
C. Variations in human skin color can be quantified, or measured.
Correct! Skin color can be quantified using devices called reflectometers, which measure the amount of light reflected by the skin. Anthropologists around the world have collected data on skin color to help learn about variations. Select another correct answer. You selected all the correct answers.
D. On average, the skin color of indigenous peoples around the world correlates with the UV intensity in their environments.
Correct! Where UV intensity is higher, the skin color of indigenous peoples tends to be darker on average. Where UV intensity is lower, the skin color of indigenous peoples tends to be lighter on average. (Note that in modern times, people often move to different places. So, the average skin color overall will not always “match” the UV intensity in an environment.) Select another correct answer. You selected all the correct answers.
A. Human populations around the globe have different versions of the MC1R gene.
It is true that there is variation in the MC1R gene among populations. But this observation did not directly help Jablonski determine a selective pressure for darker skin. Try again.
B. In general, people with more darkly pigmented skin have less folate, a nutrient important for human reproduction, circulating in their blood.
This is not one of the observations Jablonski made. In fact, it is unlikely that people with more darkly pigmented skin would have less folate in their blood, since darkly pigmented skin protects folate from being broken down by sunlight. Try again.
C. The larger amount of eumelanin in darkly pigmented skin protects circulating folate from being destroyed by UV radiation.
Correct! This observation led Jablonski to propose that the ability to maintain high levels of circulating folate, a nutrient important for human reproduction, provides a selective advantage to individuals living in a high-UV environment. So, individuals with larger amounts of eumelanin are favored in high-UV environments. Select another correct answer. You selected all the correct answers.
D. The melanin in darkly pigmented skin protects DNA from UV radiation, which can cause skin cancer.
It is true that melanin protects against skin cancer. But skin cancer usually occurs after a person’s peak reproductive years and is unlikely to affect offspring production. Traits that do not affect offspring production are unlikely to be acted on by natural selection. So, Jablonski did not think that protection against skin cancer explained the selective pressure for darker skin. Try again.
A. In general, people with lighter skin tend to have a higher risk of vitamin D deficiency.
This statement is inaccurate. Lighter skin absorbs the UV needed for vitamin D production more easily than darker skin does. So, in general, people with darker skin living in areas with low amounts of UV have a higher risk of vitamin D deficiency. Try again.
B. Red hair and light skin are most common among people of northern European descent.
This statement is generally true, but it does not provide evidence for the selective pressure in the hypothesis. Try again.
C. Indigenous peoples with darker skin who live at high latitudes have diets that consist of foods rich in vitamin D.
Correct! Populations that get enough vitamin D from their diets would experience less selection for lighter skin. So, this observation supports the hypothesis 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.
D. People with lighter skin cannot synthesize enough vitamin D in high-UV environments, such as equatorial Africa.
This statement is inaccurate. Lighter skin absorbs the UV needed for vitamin D production more easily than darker skin does. So, people with lighter skin are more likely to get enough UV to synthesize vitamin D in a wide range of environments. Try again.
A. adults with dark skin who live close to the equator
Although dark skin absorbs less UV, 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. Also, rickets affects children, not adults. (Adults can experience a similar condition known as osteomalacia.) Try again.
B. children with light skin who live close to the equator
UV radiation is most intense at the equator, so people living there have a lower risk of vitamin D deficiency and rickets than people living far from the equator. Try again.
C. adults with light skin who live far south of the equator
Although UV is less intense farther from the equator, light skin absorbs more UV than dark skin does. So, people with lighter skin have a lower risk for vitamin D deficiency than people with darker skin. Also, rickets affects children, not adults. (Adults can experience a similar condition known as osteomalacia.) Try again.
D. children with dark skin who live far north of the equator
Correct! Rickets is caused by vitamin D deficiency in children, often due to insufficient UV. Dark skin absorbs less UV than light skin does, and places far from the equator also tend to have less UV. So, this group is at the highest risk for vitamin D deficiency and rickets out of all four groups. Select another correct answer. You selected all the correct answers.
A. Some genetic variations that protect humans from malaria, a disease transmitted by mosquitoes, also cause the blood disease thalassemia.
Correct! This example describes an evolutionary trade-off because it includes both an advantage and a disadvantage. In an environment with mosquitoes that can transmit malaria, these genetic variations are an advantage. However, in the context of a blood disease, they are a disadvantage. Select another correct answer. You selected all the correct answers.
B. Some garter snakes have mutations that make them resistant to a toxin found in their prey, rough-skinned newts. Snakes with these mutations move more slowly and may not be as good at hunting or avoiding predators.
Correct! This example describes an evolutionary trade-off because it includes both an advantage and a disadvantage. When snakes are eating the rough-skinned newts, having these mutations is an advantage. But when it comes to hunting fast-moving prey or avoiding predators, having these mutations is a disadvantage. Select another correct answer. You selected all the correct answers.
C. Alleles that caused the loss of body hair allowed humans to lose heat more easily in hot environments. This in turn helped humans walk and run for longer distances to hunt large animals.
This example does not describe a trade-off because it does not mention any disadvantages. Losing heat in hot environments and walking and running for longer distances are all advantages. Try again.
D. The common Mormon butterfly is not toxic to birds and other predators. Some common Mormons have genetic variations that make them resemble toxic butterflies, which deters predators. In places without predators, common Mormons with these variations don’t live as long as other common Mormons.
Correct! This example describes an evolutionary trade-off because it includes both an advantage and a disadvantage. In an environment with predators, having these variations is an advantage because it helps the butterflies avoid the predators. In an environment without predators, having these variations is a disadvantage because it leads to a shorter lifespan. Select another correct answer. You selected all the correct answers.