Final answer:
Evolution is the process of change in a population over time, and natural selection is the mechanism by which better-adapted organisms survive and reproduce, leading to evolution.
Step-by-step explanation:
The process of change in a population over time is called evolution. Evolution occurs by a process known as natural selection, where organisms that are better adapted to the environment tend to survive and reproduce at a higher rate.
An example of this is the beak size of Darwin's finches, which changes in response to the availability of different-sized seeds. This is a characteristic that can lead to evolution of a species, as those finches with beak sizes most suited to the available seeds are more likely to survive and pass on their genes. Over time, the average beak size in the population may change, a phenomenon stemming from the principles of population genetics.
Therefore, the process of change in a population over time is called evolution, and the process by which organisms that are better adapted to the environment survive and reproduce is called natural selection.