Which of these BEST describes our current understanding about how species evolve over time?
A) As organisms use certain traits more frequently, each organism evolves over time.
B) Populations of organisms evolve rapidly due to genetic changes brought about by random mating patterns.
C) Traits that result in a greater number of mutations occur more frequently, causing the population to evolve.
D) Populations evolve as natural selection results in a change in the frequency of alleles within the population over time.