Imagine a scenario in which part of a population of South American finches is blown by a storm onto an island far offshore and manages to survive and reproduce there for a period of 10,000 years. After that period, a climate change results in lower sea levels and the reconnection of the island with the mainland. Members of the formerly isolated island finch population can now interact freely with members of the original mainland population. Which of the following observations would, by itself, lead you to conclude unequivocally that the island finch population had evolved into a distinct species?
a. The island birds all have red feathers, but the mainland birds have only green feathers.
b. Individuals from the different populations sometimes mate with each other, but all of the resulting eggs are sterile.
c. Individuals from the different populations seem to mate freely with each other, and the resulting offspring mate freely with either island birds or mainland birds.
d. Individuals from the different populations feed on the same kinds of seeds in the same habitats and frequently direct courtship behavior toward members of the other population.
e. Hybrid offspring of matings between individuals from the two populations do not look like either parent.
