The Origin of Species Revised March 2018
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The Origin of Species: The Beak of the Finch
7. Which of the five observations below provide(s) evidence that two populations are likely experiencing
reproductive isolation and that there is little if any genetic exchange between them? Select the appropriate
answer, a–d.
i. The two populations live on different islands.
ii. One population breeds in late spring and the other population breeds in late summer.
iii. One population eats mostly small, soft seeds and the other population eats mostly large, hard
seeds.
iv. The males of one population sing different songs than the males of the other population.
v. The females of the two populations look the same.
a. statement i only
b. statements iii and v only
c. statements i, ii, and iv only
d. statements ii and iv only
8. How did the Grants test their hypothesis that differences in birds’ songs can keep finches from breeding
with members of other species?
a. They watched which birds were mating with each other and listened for the songs the birds were
singing.
b. They recorded birds singing on the island of Daphne Major for an entire breeding season to see which
type of song was used more often by each species.
c. They played the songs of medium ground finches and cactus finches through a loudspeaker at different
times, when individuals from both species were present, to see which species responded to each song.
d. They played the song of the medium ground finch to medium ground finch males through a loudspeaker
to see if they would respond; they then played the song of the cactus finch to cactus finch males to see
if they would respond.
9. Explain the evidence presented in the film for your answer in question #8 above.
a. Males only came to the loudspeaker when the song of their own species was being played.
b. The type of song used more often during the breeding season was also the song sung by the most
abundant species.
c. During mating, birds sang the song of their own species.
10. Figure 1 shows the beak depths of 200 medium ground finches on Daphne Major before a severe drought
began on the island. This is a normal sample of a population of medium ground finches, similar to measured
samples from previous years. During wet years, all types of seeds are abundant. The medium ground finch
prefers to eat small, soft seeds that are easy to crush. However, during droughts, when small seeds are not
as abundant, they also eat the larger seeds on the island.
a. Make two or three observations about the distribution of beak depth measurements in this sample of
200 medium ground finches.