In paragraph 2, why does the author mention that some insect populations were separated from each other by a change in the course of Mississippi River caused by an earthquake? A. To make the point that some kind of physical barrier separates the subpopulations of most species B. To support the claim that the condition of allopatry can sometimes arise in a short time C. To provide an example of a situation in which gene flow among the subpopulations of a species happens at a slow rate D. To explain insects living along opposite shores of the Mississippi River are very different from each other