SAT Subject Biology Practice Question 341: Answer and Explanation
A population of birds (Population A) on a remote, isolated island is studied to determine beak length. The resulting data are plotted in Figure 1.
Suppose that 200 years later, the beaks of the birds on the island were again measured (Population B). The data, when plotted, yielded a graph as in Figure 2.
What is the most likely reason for the difference in distribution of beak lengths between the data plotted in Figure 1 and the data plotted in Figure 2 ?
A. All birds with beaks of 30 mm flew to a new island over the 200-year time span.
B. Birds with beaks of 30 mm were selected against.
C. Predators consumed birds with beaks of 40 mm.
D. Predators consumed birds with beaks of 20 mm.
E. Birds with beaks of 30 mm were selected for extinction.
Correct Answer: B
B Clearly the birds with 30 mm beaks were not surviving too well. There is no reason to assume they flew to another island; remember, they are on a remote, isolated island. There may not be another island near enough to fly to (A is wrong). If predators consumed birds with 20 mm or 40 mm beaks, they would not be the prevalent populations in Figure 2 (C and D are wrong), and if birds with 30 mm beaks were selected for, the population would not have been divided (E is wrong).