Question

During the drought of 1977, 84 percent of the medium ground finch population on Daphne Major disappeared. The individuals that survived had beaks that were deeper and larger than the beaks of individuals who did not survive.
Given that natural selection favored large individuals with deeper and larger beaks, how can the presence of individuals with small, pointier beaks in 1983 be explained?

A) Researchers were not measuring juvenile birds in 1977 but did measure juvenile birds in 1983. It is a well-known fact that juvenile birds are small and have small beaks.
B) These islands were colonized from the mainland. These small-beaked individuals must have flown over from Ecuador.
C) Even though the majority of birds after 1977 had deeper and larger beaks, there was still variation in beak size in the population. As seed type and seed availability changed, birds with beaks suited to exploit abundant seeds had higher reproductive success.
D) These islands must have received immigrants from a neighboring island.

Answer 1

Answer:

Even though the majority of birds after 1977 had deeper and larger beaks, there was still variation in beak size in the population. As seed type and seed availability changed, birds with beaks suited to exploit abundant seeds had higher reproductive success.

Explanation:

Natural selection favors the genetic traits that increase the chance of survival and reproduction of the individuals under the prevailing surroundings. After the drought, the finches with larger and deeper beaks were present in the population as they were better able to survive.  

However, the population had genetic variations with regard to the beak size and the gene for small and pointier beak was also present in the gene pool. Changes in the conditions, such as seed type and availability led to the natural selection of small and pointier beaks that were able to survive and reproduce under the present conditions.