Final answer:
Incremental evolution, or microevolution, refers to small, gradual evolutionary changes, while exaptation is the repurposing of a trait for a function other than what it was originally selected for. Evolution can be slow or rapid depending on environmental factors, and it is a dynamic, non-goal-directed process.
Step-by-step explanation:
The distinction between incremental evolution and exaptation lies in the mechanisms and pace at which evolutionary changes occur. Incremental evolution, or microevolution, refers to small, gradual changes in a species over time through mutations that provide either advantages or disadvantages. These gradual changes can lead to new species over long periods. Exaptation, on the other hand, involves traits that evolve for certain functions but are later repurposed for different functions not related to the original selective pressures. For instance, feathers initially evolved for insulation could become useful for flight in birds, representing exaptation.
While evolution typically occurs slowly and is not easily observable from one generation to the next, such as the evolution of a common ancestor of hippos into whales, there is also evidence for rapid adaptation. This can happen due to sudden environmental changes or introduction of new genetic lineages, which may lead to drastic changes in a species. An example includes the cane toad, where changes in leg length were observed in relation to their invasion progress.
In essence, evolution is not goal-directed but a response to environmental changes. Traits that are advantageous in one particular environment at a specific time might no longer be so in the future, highlighting the dynamic nature of evolutionary processes.