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Different finch species have beaks of different shapes and sizes. What do these beak differences tell us?
The different beak shapes are each suited for different types of food. As Rosemary Grant says, “Beaks are tools, and you need the right tool for the right job.” Try again.
Recall from the film that evidence for evolutionary relationships and common ancestry among finch species came primarily from DNA analysis. Also, similarities in traits, rather than differences, would provide evidence for shared ancestry. Try again.
Correct! Having a beak shape well-adapted for obtaining and manipulating/eating a particular type of food in a given environment (i.e., a seed of a certain size and shape or nectar from certain plants) is critical to survival. Select another correct answer. You selected all the correct answers.
This would be a possible scenario. However, recall from the film that DNA evidence suggests that the Galápagos finches all evolved from a single ancestor that came from the mainland. Try again.
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Genetic evidence supports which of the following explanations for the presence of 13 different finch species on the Galápagos Islands?
Though plausible, DNA evidence does not support this hypothesis. Recall that the Galápagos finches are more closely related to each other than to any other species on the mainland. Try again.
DNA evidence does not support this hypothesis. Recall that the Galápagos finches are more closely related to each other than to any other species on the mainland. Try again.
It’s true that these are the two possible scenarios for how the Galápagos finch species could have evolved, but recall that Dr. Peter Grant says DNA evidence provides clear evidence for only one of these two. Try again.
Correct! The Galápagos finch DNA reveals that the finch species are more related to each other than to any species on the mainland. Select another correct answer. You selected all the correct answers.
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In 1977, Daphne Major experienced a severe drought. The figure shows the beak depths of the initial population of medium ground finches before the drought (red bars), and of the drought survivors (black bars). What do the data show? Select all that apply.
Correct! The tallest red bar is at 8.8 mm. This means a greater number of finches in the original population had a beak depth of 8.8 mm (around 48 birds) than any other beak depth. The black bar at 8.8 mm on the other hand is very small, which means very few birds with this beak depth survived the drought. Select another correct answer. You selected all the correct answers.
Correct! Together, the black bars fill less than half of all the red bars, which means that fewer than half of the birds of the initial population survived the drought. Select another correct answer. You selected all the correct answers.
It’s true that the most common beak depth of the surviving population was 10.3 mm as the tallest black bar is 10.3 mm. However, this black bar is just a bit less than half of the red bar, which means that nearly half (~40%) of the individuals with beak depths of 10.3 mm from the initial population survived the drought. Try again.
Correct! Most of the survivors of the 1977 drought had larger beaks. When small seeds became scarce after the drought, more medium ground finches with smaller beaks ran out of food and died. Finches with larger beaks were better able to eat the larger, harder seeds. Select another correct answer. You selected all the correct answers.
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The top figure shows the beak depths of the 1976 finch population (red bars) before the drought, and the population after the drought (black bars). The lower figure shows the beak depths of the offspring of the drought survivors in 1978. What do these figures tell us?
Correct! If you compare the red bars in the first graph to the red bars in the second graph, the distribution is skewed to the right in the second graph, which is an indication that, on average, beak depth increased. The film mentions that the average beak depth of the population increased by more than 4% in just one generation. Select another correct answer. You selected all the correct answers.
Most finches that survived the drought had beak depths of 9.8 mm and 10.3 mm. The most common beak depth of the offspring was around 9.3 mm and 9.8 mm. So the beaks of the offspring were not much larger than those of their parents. Try again.
The range of offspring beak depths is larger than that of the parents that survived the 1977 drought (black bars). The range is 7.3 mm to 11.3 mm for the offspring and 7.8 mm to 10.8 mm for the parents. Try again.
The 1978 offspring population shows recovery; their numbers (~120) far exceed those of their drought-surviving parents (~40). However, they do not outnumber the ~200 birds in the initial population before the drought. Try again.
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The Grants witnessed strong selection during the droughts in 1977 and 1985. Compare the two droughts. Select all that apply.
Recall that one of the two droughts was preceded by an unusually wet season, which changed the vegetation prior to the drought. As a result, the two droughts affected the vegetation in different ways. One drought made larger seeds more abundant than small seeds, whereas the other drought made smaller seeds more abundant than large ones. Try again.
Correct! In both droughts, food became scarce. Finches had to compete for scarce food, and birds with certain beak depths that were better able to eat the available seeds survived. Natural selection favors traits, such as beak depth, that provide a survival or reproductive advantage in a particular environment. If the environment changes, natural selection may favor a different trait. Select another correct answer. You selected all the correct answers.
Correct! Both droughts resulted in one type of seed becoming more abundant than the other. Finches with beak depths better suited to that seed type had a survival advantage. Select another correct answer. You selected all the correct answers.
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How did the Grants test their hypothesis that differences in the finch songs can keep different species of finches from breeding with one another?
Recall that the Grants and their team conducted an experiment using recorded finch songs. Try again.
The song that male finches sing is characteristic for that particular finch species. Merely recording which songs are sung most often would not reveal how song keeps species apart. Try again.
This is something that the Grants did do. The work showed that males recognize females of their own species based on appearance. This part of the experiment, however, did not reveal anything about how song keeps species apart. Try again.
Correct! The Grants’ experiments using recorded finch songs showed that finch species respond to their own song and not to the songs of other species. The fact that species differences in finch song keep species apart is an example of reproductive isolation. Select another correct answer. You selected all the correct answers.
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The film defines species as populations whose members don't interbreed. What keeps different Galápagos finch species from mating? Select all that apply.
Correct! In general, female finches only recognize and respond to males that sing their species’ song. They will ignore singing males of other species. Select another correct answer. You selected all the correct answers.
Recall from the film that eating different types of food is not what keeps different finch populations from mating. The medium ground finches, for example, had slight variations in beak depth that made some individuals better suited to eat one type of seed over another. But these birds were still able to mate with each other and were part of the same species. Try again.
Correct! The Grants and their team gathered evidence to show that finches choose mates on the basis of certain traits that differ among species. These differences arose as geographically isolated populations changed over time in different ways (i.e., without mixing their genes). Select another correct answer. You selected all the correct answers.