Which of the following is not included in the theory of natural selection?

The option that is not included in the theory of natural selection is the "disappearance of functionless organs". This is because natural selection does not necessarily lead to the disappearance of functionless organs, but rather to the preservation of traits that enhance an organism's ability to survive and reproduce. Functionless organs may persist in a population if they do not affect an organism's fitness, or if they have secondary functions that are beneficial. Additionally, some functionless organs may be vestigial structures that have lost their original function over time, but are still present in a population due to historical reasons. Overall, the theory of natural selection is concerned with the mechanisms that lead to the evolution of traits that enhance an organism's fitness, rather than the disappearance of particular structures.