Natural Selection (SI)

Suppose a small island is home to two troops of monkeys. Every year, a certain fraction of each troop of monkeys are killed by predators. Every summer, each surviving pair of monkeys has one child. In this simplified model, the monkey population would look something like the one shown. The first troop spends more time on the ground. The second troop spends more time in the trees. Compare the sizes of the two monkey troops through time. Which of the following statements about the monkey troops is true?

• Because members of the second troop were better able to avoid predators, more of them were able to reproduce.
• Because members of the first troop were better able to avoid predators, more of them were able to reproduce.
• Because members of the first troop were better able to reproduce, more of them were able to avoid predators.
• Because members of the second troop were better able to reproduce, more of them were able to avoid predators.

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The process of natural selection favors certain characteristics in organisms, while it selects against other characteristics. What would happen if there was zero variation between all of the organisms on Earth?

• Evolution through natural selection would not occur.
• Less food would be available.
• Natural selection would operate faster.
• Organisms would evolve to increase variety.

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Natural selection requires that individuals in a population are

• genetically diverse.
• exactly identical.
• small in size.
• only physically different.

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Trees need water so they can make their own food. Trees take in water using their roots. If a drought occurred—reducing the amount of available water—some trees, such as those with deep roots that can reach the water table, would be naturally selected over other trees. If the drought continued for an extended period of time, the trees would likely evolve until most of the trees possessed drought-resistant characteristics. Which of the following allows natural selection and evolution to occur?

• differences in the characteristics of individual trees
• increasing the height of the water table
• using other plant parts instead of roots to absorb water
• having an identical genetic make-up

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Suppose a population of rabbits is introduced to an environment that has hot summers and extremely cold winters. Every winter, many rabbits die because of the cold and the lack of food. The rabbits have a range of ear sizes. Rabbits lose a lot of their body heat through their ears. Every winter, more of the large-eared rabbits die than the others. Every summer, more of the short-eared rabbits die than the others. At first, there are an equal number of rabbits with each size of ears. After several years, what will the frequency of ear sizes in the population be like?

• There will be more rabbits with medium ears than any of the others.
• There will be fewer rabbits with large ears than any of the others.
• There will be an equal number of rabbits with each ear size.
• There will be more rabbits with large ears than any others.

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Peppered moths use the adaptation of camouflage as protection from predators. They may have a variety of colors or shades, but before the Industrial Revolution, they were typically white with black speckles. The Industrial Revolution in the 1880s introduced large-scale pollution into the environment. The pollution resulted in widespread, dark-colored staining of buildings and trees. Which of the following was the most likely effect of the Industrial Revolution on peppered moths in cities?

• The population of light-colored moths decreased and the population of dark-colored moths increased.
• The peppered moths adapted an improved sense of sight and smell.
• Over time, the white, speckled moths were outnumbered by plain white moths.
• The peppered moths developed a tolerance to smog and chemical waste.

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Black squirrels are the same species as gray squirrels. A single litter of squirrels can have both black and gray squirrels. Over the past century, the percent of squirrels in the vicinity of Washington, DC, that are black instead of the more common gray has been continually increasing. Which of the following statements best explains why this is happening?

• Black squirrels have a survival advantage over gray squirrels.
• Gray squirrels are more comfortable with humans than black squirrels.
• Black squirrels are more popular with tourists than gray squirrels.
• Black squirrels are more visible against tree trunks than gray squirrels.

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A deer is born with the ability to smell predators better than the other deer in its population. As a result, this deer has several seconds of warning every time wolves or other predators attack. This trait may be selected by natural selection because it increases the deer's _______.

• ability to survive
• ability to find food
• sense of safety
• ability to select mates

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Which of the following best describes how a species changes over time?

• Members of a species that are best adapted to survive produce offspring with similar characteristics, while members with unfavorable traits do not survive.
• Members of a species with unfavorable traits produce offspring with similar characteristics, while members best adapted to survive do not reproduce.
• Members of a species that are best adapted to survive and members with unfavorable traits both produce the same number of offspring.
• Diversity among members of the species causes all members to stop producing offspring.

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The medium ground finch lives on the Galapagos Islands. Birds with beaks of all sizes were originally part of this population. The finches are seed eaters. The types of food available for them to eat depends on the weather. During wet years, there is a large variety of food. During dry years, there is less food, and large, tough seeds are more abundant than small seeds. After a long drought, researchers noticed certain differences in the population of medium ground finches living compared to those who lived before the drought. What was different about the finches after the drought?

• They had larger beaks.
• They had larger wings.
• They were a new species.
• They had smaller wings.

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