Calvaria major is a rare but once-abundant tree found on the island of

Calvaria major is a rare but once-abundant tree found on the island of Mauritius, which was also home to the dodo, a large flightless bird that became extinct about three centuries ago. In 1977 Stanley Temple, an ecologist whose investigation of Calvaria major was a sidelight to his research on endangered birds of Mauritius, proposed that the population decline of Calvaria major was linked to the demise of the dodo, a hypothesis that subsequently gained considerable currency. Temple had found only thirteen Calvaria major trees on Mauritius, all overmature and dying, and all estimated by foresters at over 300 years old. These trees produced fruits that appeared fertile but that Temple assumed could no longer germinate, given his failure to find younger trees.

The temporal coincidence between the extinction of the dodo and what Temple considered the last evidence of natural germination of Calvaria major seeds led him to posit a causal connection. Specifically, he hypothesized that the fruit of Calvaria major had developed its extremely thick-walled pit as an evolutionary response to the dodo’s habitual consumption of those fruits, a trait enabling the pits to withstand the abrasive forces exerted on them in the birds’ digestive tracts. This defensive thickness, though, ultimately prevented the seeds within the pits from germinating without the thinning caused by abrasion in the dodo’s gizzard. What had once been adaptive, Temple maintained, became a lethal imprisonment for the seeds after the dodo vanished.

Although direct proof was unattainable, Temple did offer some additional findings in support of his hypothesis, which lent his argument a semblance of rigor. From studies of other birds, he estimated the abrasive force generated within a dodo’s gizzard. Based on this estimate and on test results determining the crush-resistant strength of Calvaria major pits, he concluded that the pits could probably have withstood a cycle through a dodo’s gizzard. He also fed Calvaria major pits to turkeys, and though many of the pits were destroyed, ten emerged, abraded yet intact. Three of these sprouted when planted, which he saw as vindicating his hypothesis.

Though many scientists found this dramatic and intriguing hypothesis plausible, Temple’s proposals have been strongly challenged by leading specialists in the field. Where Temple had found only thirteen specimens of Calvaria major, Wendy Strahm, the foremost expert on the plant ecology of Mauritius, has identified hundreds, many far younger than three centuries. So Calvaria major seeds have in fact germinated, and the tree’s reproductive cycle has thus continued, since the dodo’s disappearance.

Additional counterevidence comes from horticultural research by Anthony Speke, which shows that while only a minority of unabraded Calvaria major seeds germinate, the number is still probably sufficient to keep this species from becoming extinct. The population decline, while clearly acute, could easily be due to other factors, including disease and damage done by certain nonindigenous animals introduced onto Mauritius in the past few centuries.

1. Which one of the following most accurately expresses the main point of the passage?

(A) Calvaria major germination, though rare, is probably adequate to avoid extinction of the species.
(B) The appeal of Temple’s hypothesis notwithstanding, the scarcity of Calvaria major is probably not due to the extinction of the dodo.
(C) Temple’s experimentation with Calvaria major pits, though methodologically unsound, nevertheless led to a probable solution to the mystery of the tree’s decline.
(D) Temple’s dramatic but speculative hypothesis, though presented without sufficient supporting research, may nevertheless be correct.
(E) Calvaria major would probably still be scarce today even if the dodo had not become extinct.


2. The author indicates that Temple’s research on birds of the island of Mauritius

(A) was largely concerned with species facing the threat of extinction
(B) furnished him with the basis for his highly accurate estimates of the crush-resistant strength of Calvaria major pits
(C) provided experimental evidence that some modern birds’ gizzards exert roughly the same amount of abrasive force on their contents as did dodo gizzards
(D) was comprehensive in scope and conducted with methodological precision
(E) was originally inspired by his observation that apparently fertile Calvaria major pits were nevertheless no longer able to germinate


3. In saying that Temple’s supporting evidence lent his argument a “semblance of rigor” (Highlighted), the author most likely intends to indicate that

(A) despite his attempts to use strict scientific methodology, Temple’s experimental findings regarding Calvaria major pits were not carefully derived and thus merely appeared to support his hypothesis
(B) direct proof of a hypothesis of the sort Temple was investigating is virtually impossible to obtain, even with the most exact measurements and observations
(C) in contrast to Temple’s secondhand information concerning the age of the thirteen overmature Calvaria major trees he found, his experiments with turkeys and other birds represented careful and accurate firsthand research
(D) in his experimentation on Calvaria major pits, Temple produced quantitative experimental results that superficially appeared to bolster the scientific credibility of his hypothesis
(E) although the consensus among experts is that Temple’s overall conclusion is mistaken, the scientific precision and the creativity of Temple’s experimentation remain admirable


4. The passage indicates which one of the following about the abrasion of Calvaria major pit walls?

(A) Thinning through abrasion is not necessary for germination of Calvaria major seeds.
(B) In Temple’s experiment, the abrasion caused by the digestive tracts of turkeys always released Calvaria major seeds, undamaged, from their hard coverings.
(C) Temple was mistaken in believing that the abrasion caused by dodos would have been sufficient to thin the pit walls to any significant degree.
(D) Abrasion of Calvaria major pit walls by the digestive tracts of animals occurred commonly in past centuries but rarely occurs in nature today.
(E) Temple overlooked the fact that other natural environmental forces have been abrading Calvaria major pit walls since the dodo ceased to fulfill this role.


5. It can be most logically inferred from the passage that the author regards Temple’s hypothesis that the extinction of the dodo was the cause of Calvaria major’s seeming loss of the ability to reproduce as which one of the following?

(A) essentially correct, but containing some inaccurate details
(B) initially implausible, but vindicated by his empirical findings
(C) an example of a valuable scientific achievement outside a researcher’s primary area of expertise
(D) laudable for its precise formulation and its attention to historical detail
(E) an attempt to explain a state of affairs that did not in fact exist


6. Based on the passage, it can be inferred that the author would be likely to agree with each of the following statements about Calvaria major EXCEPT:

(A) The causes of the evolution of the tree’s particularly durable pit wall have not been definitively identified by Temple’s critics.
(B) The notion that the thickness of the pit wall in the tree’s fruit has been a factor contributing to the decline of the tree has not been definitively discredited.
(C) In light of the current rate of germination of seeds of the species, it is surprising that the tree has not been abundant since the dodo’s disappearance.
(D) There is good reason to believe that the tree is not threatened with imminent extinction.
(E) Calvaria major seeds can germinate even if they do not first pass through a bird’s digestive system.