The Origin of Species: The Beak of the Finch

Which is the most likely explanation for the presence of 13 different finch species on the Galápagos Islands today?

• Many years ago, several different species of birds migrated to the islands and the 13 finch species that currently live there are the only species that survived.

• Many years ago, a small population of a single bird species migrated to the islands and evolved into the 13 species that live on the islands today.

• Each of the 13 species has migrated to the islands at different times over the years.

• A single bird species migrated to one island at around the time of Charles Darwin’s voyage to the Galápagos and then migrated to all 13 islands.

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Different finch species have beaks of different shapes and sizes. These different beak structures are evidence of

• different finch species adapting to different environments over many generations.

• different finch species with different beak structures coming to the Galápagos Islands from the mainland.

• different finch populations being evolutionarily related.

• individual birds changing their beak characteristics so that they could feed efficiently.

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Examine the phylogenetic tree of the 13 finch species below. Which of the following statements is a correct interpretation of the phylogenetic tree in the illustration?

• The sharp-beaked ground finch is more closely related to the small tree finch than either species is to the cactus finch.

• The warbler finch is the common ancestor to all the finch species that exist today in the Galápagos Islands.

• All the Galápagos finches are more closely related to one another than they are to mainland finch species.

• The 13 finch species evolved in sequence; the warbler finch is the oldest species and the small ground

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Which experimental data from the film provide the best evidence that the cactus finch and the medium ground finch on Daphne Major are distinct species?

• Many more medium ground finches than cactus finches died in response to the drought.

• Cactus finch and medium ground finch males attempted to breed only with females of their own species

• The cactus finch and medium ground finch feed on different types of food.

• Medium ground finch and cactus finch females have different markings and feather color

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Imagine you are studying a population of finches on one of the Galápagos Islands. You have been recording many of the birds’ physical traits, including the length of both wings. You observe that for 80% of individuals measured, the length of the left wing is not significantly different from the length of the right wing (in other words, they are symmetrical). But for about 20% of birds measured, the wing lengths are asymmetrical. This distribution is true from generation to generation. Suddenly, a rare 5-day windstorm takes over the island. After the storm, you spend the next several days netting each bird on the island that survived the storm. You discover that 85% of the birds with symmetrical wings survived the storm, whereas only 5% of the birds with asymmetrical wings did.

a. Propose a hypothesis to explain this observation.

b. If such storms become increasingly common due to changes in climate, how might you expect the population to change over time with respect to wing symmetry?

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How did the Grants test their hypothesis that differences in birds’ songs can keep finches from breeding with members of other species?

• They watched which birds were mating with each other and listened for the songs the birds were singing.

• 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.

• 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.

• 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.

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