Two closely related populations of mice have been separated for many generations by a river. Climatic change causes the river to dry up, thereby bringing the mice populations back into contact in a zone of overlap. Which of the following is not a possible outcome when they meet?
A) They interbreed freely and produce fertile hybrid offspring.
B) They no longer attempt to interbreed.
C) They interbreed in the region of overlap, producing an inferior hybrid. Subsequent interbreeding between inferior hybrids produces progressively superior hybrids over several generations.
D) They remain separate in the extremes of their ranges but develop a persistent hybrid zone in the area of overlap.
E) They interbreed in the region of overlap, but produce sterile offspring

The correct answer is B) they no longer attempt to interbreed.

Explanation:

This question speaks to Speciation and Natural Selection.

What is a species? A species is a group of organisms that are theoretically able to interbreed in order to produce viable offspring.

We say "theoretically," because members of the same species might be geographically isolated (on an island, for example) and yet, if they were able to get together, they could successfully mate because they are wild animals.

A "population" is a subset of a species, and is comprised of organisms of the same species but which live in close proximity and interact with each other, and therefore have an actual chance of mating.

If members of different species attempt to interbreed, the result is usually null.

A species, by definition, is reproductively isolated from other species.

Occasionally, a sterile hybrid can form if closely related species mate.

For example, horses and donkeys are two different, but closely related, species. Horses and donkeys can interbreed, but their offspring, mules, are sterile.

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