Which of the following factors is involved in natural selection?

Natural selection is a fundamental mechanism of evolution characterized by the differential survival and reproduction of individuals based on their traits which are influenced by environmental pressures. The critical factor in this process is the competition for resources among individuals in a population. When resources such as food, water, or mates are scarce, individuals with advantageous adaptations are more likely to survive and reproduce, thereby passing these beneficial traits to their offspring.

This competitive interaction drives natural selection by favoring individuals that are better suited to their environment, which leads to evolutionary changes in the population over time. In contrast, the other factors listed do not contribute to the process of natural selection: random mutations may introduce genetic variation, but they are not influenced by environmental pressures, equal reproductive success means no advantage for particular traits, and the absence of environmental pressures negates the selection process altogether. Therefore, competition for resources is essential for natural selection to occur, making it the key factor in this evolutionary mechanism.