Making Inferences in Science Passages - HSPT Reading

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Adapted from “Birds in Retreat” in “Animal Defences—Active Defence” in Volume Four of The Natural History of Animals: The Animal Life of the World in Its Various Aspects and Relations by James Richard Ainsworth Davis (1903)

Among the large running birds are forms, like the African ostrich, in which the absence of powers of flight is largely compensated by the specialization of the legs for the purpose of rapid movement on the ground. For straightforward retreat in open country nothing could be more effective; but another kind of adaptation is required in birds like rails, which are deficient in powers of flight, and yet are able to run through thickly-growing vegetation with such rapidity as to commonly elude their enemies. This is rendered possible by the shape of their bodies, which are relatively narrow and flattened from side to side, so as to easily slip between the stems of grasses, rushes, and similar plants. Anyone who has pursued our native land-rail or corn-crake with intent to capture will have noted how extremely difficult it is even to get within sight of a bird of this sort.

Certain birds, unfortunately for themselves, have lost the power of flight without correspondingly increased powers of running, and have paid the penalty of extinction. Such an arrangement, as might be anticipated, was the result of evolution in islands devoid of any predatory ground-animals, and a classic example of it is afforded by the dodo and its allies, birds related to the pigeons. The dodo itself was a large and clumsy-looking species that at one time abounded in the island of Mauritius, which, like oceanic islands generally, possessed no native mammals, while its indigenous reptiles were only represented by lizards. The ubiquitous sailor, however, and the animals (especially swine) which he introduced, brought about the extinction of this helpless bird in less than a century after its first discovery in 1598. Its memory is now only kept green by a few contemporary drawings and descriptions, certain museum remains, and the proverb "as extinct as a dodo.” A similar fate must overtake any organism suddenly exposed to new and unfavorable conditions, if devoid of sufficient plasticity to rapidly accommodate itself to the altered environment.

Which of the following can we infer based on the passage?

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Answer

This may seem like a tricky question, but let’s consider each of the answer choices individually:

“If sailors had visited Mauritius sooner, dodos might still be alive today.”: The passage doesn’t support this assertion at all. Since the arrival of sailors on New Zealand is identified as the cause of the dodo’s extinction, it doesn’t make sense that the dodo would have survived if the sailors would have arrived earlier; it would probably have gone extinct sooner, based on the passage’s logic.

“Ostriches would likely be as effective at running away from predators in tall grass as in open country.”: The passage specific disproves this when it says of ostriches and their running abilities, “For straightforward retreat in open country nothing could be more effective; but another kind of adaptation is required in birds like rails, which are deficient in powers of flight, and yet are able to run through thickly-growing vegetation with such rapidity as to commonly elude their enemies.” This suggests that ostriches are better adapted to surviving in open country than in areas covered by tall grass.

“The land-rail and corn-crake are not well adapted to running through tall grass.”: The passage disproves this answer choice when it describes the ability of rails to run through tall grass: “This is rendered possible by the shape of their bodies, which are relatively narrow and flattened from side to side, so as to easily slip between the stems of grasses, rushes, and similar plants.” After this sentence, the author mentions land-rails and corn-crakes’ abilities to evade hunters, so we can assume that these birds are well adapted to running through tall grass.

“Lizards were a predator of dodos.”: This can’t be true, because the passage tells us that “The dodo . . . was a large and clumsy-looking species that at one time abounded in the island of Mauritius, which, like oceanic islands generally, possessed no native mammals, while its indigenous reptiles were only represented by lizards.” Given that when animals that preyed on the dodo were introduced to Mauritius, the dodo went extinct, we can assume that since the lizards and dodos coexisted before this point, the lizards did not prey on the dodos. If this were true, the dodos would likely have learned to run or fly away, which they did not.

This brings us to the remaining answer choice, the correct one: “If predatory ground-animals had lived on Mauritius, the dodo would have probably evolved to fly or run.” The author attributes the dodo’s extinction to the fact that it did not have to adapt and defend itself from any predators before humans introduced new species on Mauritius. From this, we can infer that if those species had been present, the dodo would have learned to fly, or, like the ostrich and the rail, would have learned to run to defend itself.

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