Final answer:
Option (A), Fish populations in different ponds may become separate species due to genetic drift, a random process that causes allele frequencies to change in isolated populations.
Step-by-step explanation:
Fish populations that do not interbreed because they live in different ponds may evolve into separate species due to genetic drift. This phenomenon often occurs in small, isolated populations where chance events can cause an allele to become more or less common purely by chance. Over time, the cumulative effect of genetic drift can lead to significant differences in the genetic composition of separate populations, potentially resulting in speciation.
This is different from artificial selection, which involves human intervention, and increased gene flow, which tends to homogenize populations rather than separate them. In contrast, large population size can reduce the chances of genetic drift having a significant impact.