Final answer:
Natural selection repurposes existing structures, behaviors, or genes through a process called preadaptation or exaptation, highlighting the importance of adaptation in evolution for an organism's survival.
Step-by-step explanation:
When natural selection repurposes existing structures, behaviors, or genes, this is called a preadaptation or exaptation. An organism may have features that were originally for a specific function, but these can be co-opted for a completely different use due to natural selection. This process highlights how adaptation is a key aspect of evolution, where the range of genetic variation modifies over time, increasing or maintaining the population's adaptation to its environment. For example, the webbed feet of a platypus are an adaptation for swimming, and a cheetah's fast speed is an adaptation for catching prey. This ability to adapt is essential for the survival and reproduction of the organism within its particular habitat.