A species of birds lives on an island. The thickness of the birds' beaks varies within the population. The birds feed mainly on seeds from plants. Birds with thinner beaks can eat only small seeds. Only birds with thicker beaks can crush and eat large seeds.

There are many small seeds during years with more rain. During dry years, there are very few small seeds and many large seeds. The large seeds are harder to crush than small seeds.

The graph below shows the average beak thickness in the bird population from 1979 to 1985: 1980 and 1982 were dry years; 1984 was a wet year; 1979, 1981, 1983, and 1985 received normal rainfall.

• Explain why the average beak thickness changed between wet and dry years.
• Explain how beak thickness would have changed during the next ten years, 1986 to 1996, if these years were wet years.
• Name the process that led to this change.

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Researchers are studying slider turtles. Slider turtles hatch on the beach. The researchers discovered that larger baby turtles were more likely to survive than smaller baby turtles. They hypothesized that the larger turtles could move more quickly toward the water than the smaller turtles, reducing their exposure to predators.

The survival advantage for the larger baby turtles is a result of

The figure below shows the skeletal structure of a seal's flipper and a monkey's arm.

The skeletal structures of the flipper and the arm are similar, even though they have different functions. Seals use their flippers for swimming, while monkeys use their arms primarily for grasping and lifting.

The seal's flipper and the monkey's arm differ in appearance. This difference is the result of

The ears of foxes help to regulate body heat. The fennec fox lives in the North African desert and has large ears that release body heat. The Arctic fox lives in cold climates and has small ears that conserve body heat.

Which of these processes led to the development of different ear sizes in foxes?

Students conducted an experiment to test the effect of antibiotics on bacteria. They placed bacteria in a petri dish that contained agar treated with an antibiotic. Only one of the bacterial colonies survived.

Which of these statements best explains why only one colony survived?

Amphibians were the first vertebrates to live on land. The ancestors of amphibians were probably lobe-finned fish. The diagram below shows this development of amphibians over time.

Which of these terms best describes how amphibians could have developed from lobe-finned fish?

Marine and land iguanas are two different species that inhabit the Galapagos Islands. Some scientists believe that both species diverged from a common ancestor. Marine iguanas eat algae. Land iguanas feed on cacti. Algae are more abundant in the ocean than cacti are on the islands. Both species lay their eggs in the sand.

Rats, cats, and goats have recently been introduced to the islands. Rats often feed on iguana eggs, cats eat baby iguanas, and goats eat cacti.

Explain how the two species of iguanas could have developed from a common ancestor. In your response, be sure to

• name the process that explains how marine and land iguanas developed from a common ancestor
• describe the steps involved in this process
• explain how the introduction of rats, cats, and goats might affect both iguana species

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Use the information and the figure below to answer the following question.

Male fiddler crabs attract females by quickly waving their large front claw. If a claw is lost in a fight or accident, they quickly grow a hollow claw of equal length. Because the new claw is lighter, they can wave it faster. A male fiddler crab is shown below.

The male fiddler crab’s new claw can be described as

Use the information and the figure below to answer the following question.

Male fiddler crabs attract females by quickly waving their large front claw. If a claw is lost in a fight or accident, they quickly grow a hollow claw of equal length. Because the new claw is lighter, they can wave it faster. A male fiddler crab is shown below.

The new claw probably helps the male fiddler crab to