Final answer:
Microevolution describes changes within a population due to mutation, selection, gene flow, and genetic drift. Macroevolution involves the broader changes that lead to new species and evolutionary groups over long timescales.
Step-by-step explanation:
The difference between microevolution and macroevolution lies in the scale and processes of evolutionary change. Microevolution refers to the changes in allele frequencies that occur over time within a population. This can result from processes such as mutation, selection, gene flow, and genetic drift, leading to adaptations to the environment or changes in the population's genetic makeup. On the other hand, macroevolution goes beyond the boundaries of a single species, encompassing the broader changes that lead to the emergence of new species (speciation), the extinction of species, and the evolution of major evolutionary groups over long geological timescales.
To clarify with an example, imagine you are observing a population of beetles. If over several generations, you start to notice more beetles with a certain coloration because that color gives them an advantage to survive or reproduce—that's an example of microevolution in action. When you're looking at the bigger picture—such as how insects evolved from a common ancestor or how different species of beetles diverged from one another—that involves macroevolution.
The correct answer to the question provided would therefore be (a) Microevolution occurs within a single population, while macroevolution occurs among different populations.