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AP Biology — Unit 7 — Natural Selection & Continuing Evolution — Drill 33

Drill 33 ·

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About This Drill

AP Biology — Unit 7 — Natural Selection & Continuing Evolution — Drill 33 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

Analyze the landmark Peter and Rosemary Grant study on natural selection in Galápagos finches. Use the breeder's equation and survivor data to evaluate claims about evolutionary change in response to environmental pressure.

Passage

Researchers studying beak depth in medium ground finches (Geospiza fortis) on the Galápagos island of Daphne Major collected beak depth measurements annually from 1976 to 1978, during which conditions were relatively stable. In 1977, a severe drought eliminated most small, soft seeds. Only large, hard seeds (requiring deep, powerful beaks to crack) remained available. Researchers documented mortality and the beak depths of survivors through the 1977–1978 drought period.
Table 1. Mean beak depth (mm) of the G. fortis population before and after the 1977 drought, and the heritability estimate for beak depth.
MeasurementValue
Mean beak depth, pre-drought (1976)9.42 mm
Mean beak depth, survivors (1978)9.96 mm
Narrow-sense heritability (h²)0.79
Estimated selection differential (S)+0.54 mm

Note: The selection differential (S) is the difference between the mean of survivors and the pre-drought population mean. The response to selection (R) is predicted by the breeder's equation: R = h² × S.

Questions in This Drill

  1. Using the breeder's equation (R = h² × S) and the data in Table 1, what is the predicted response to selection (R)?
  2. The heritability estimate (h² = 0.79) for beak depth in this population indicates which of the following?
  3. A researcher claims: "The 1977 drought demonstrates that natural selection can produce measurable evolutionary change within a single generation." Which of the following, if true, would most strongly support this claim?
  4. After the drought ended and normal rainfall returned, researchers observed that mean beak depth gradually declined back toward pre-drought values. Which of the following best explains this pattern?
  5. The G. fortis beak study is often cited as evidence that evolution is ongoing. Which feature of the study most directly supports this interpretation?