akela wrote:
Researcher: Over the course of three decades, we kept records of the average beak size of two populations of the same species of bird, one wild population, the other captive. During this period, the average beak size of the captive birds did not change, while the average beak size of the wild birds decreased significantly.
Which one of the following, if true, most helps to explain the researcher’s findings?
(A) The small-beaked wild birds were easier to capture and measure than the large-beaked wild birds.
(B) The large-beaked wild birds were easier to capture and measure than the small-beaked wild birds.
(C) Changes in the wild birds’ food supply during the study period favored the survival of small-beaked birds over large-beaked birds.
(D) The average body size of the captive birds remained the same over the study period.
(E) The researcher measured the beaks of some of the wild birds on more than one occasion.
The beak size did not change among the captive birds which means that it is not a natural phenomenon. The birds don't naturally evolve into smaller beak size birds.
Hence, there must be something going on in the wild because of which the average beak size is reducing. We are comparing the case of 30 years ago with the case of today.
(A) The small-beaked wild birds were easier to capture and measure than the large-beaked wild birds.Note that if this is true today, it must have been true 30 years ago too. If small beaked are generally easier to capture then 30 years ago also they would have been a larger proportion of the sample than in the actual population. This option doesn't tell us that anything has changed in the last 30 years. Has it become even easier to catch small beaked birds today? It doesn't say. It just says that it is easier to catch and measure small beaked birds. Then if the bird population has not changed then if 70% birds captured today are small beaked then they would have made 70% of the group 3 decades ago also. Hence, why has their percentage increased in our sample, we don't know.
swikrityC - Does this help?
(B) The large-beaked wild birds were easier to capture and measure than the small-beaked wild birds.Same logic as above. We don't need to evaluate it at all. We know that this statement doesn't give us any difference between 30 years ago and today.
(C) Changes in the wild birds’ food supply during the study period favored the survival of small-beaked birds over large-beaked birds.This makes sense. If wild food supply has favoured small beaked birds in the last 30 years, it means they flourished more than large beak birds. So then this certainly explains why more birds are small beak birds today.
It gives us a difference between the case 30 years ago and the case today.
(D) The average body size of the captive birds remained the same over the study period.
Irrelevant. We are only discussing beak size.
(E) The researcher measured the beaks of some of the wild birds on more than one occasion.
Again, doesn't matter. We don't know which birds were measured multiple times. It doesn't say that specifically small beaked birds were measured again and again.
Answer (C)
close
26 Nov 2018, 09:27
25%
(medium)
26%
(01:56)
wrong 
