Which of the following describes adaptive radiation?

Adaptive radiation refers specifically to the phenomenon where a single ancestral species rapidly diversifies into a wide variety of forms to adapt to different environments or ecological niches. This process typically occurs when organisms colonize a new area with diverse habitats or after a mass extinction event that opens up ecological opportunities.

The rapid evolution aspect highlights how quickly multiple species can respond to these new challenges and opportunities, often leading to significant morphological and behavioral differences suited to their specific environments. The evolution of Darwin's finches in the Galápagos Islands is a classic example of adaptive radiation, where these birds evolved different beak shapes and sizes to exploit various food sources.

The other options don't accurately capture the essence of adaptive radiation. The slow process of change in one species describes gradual evolution but lacks the component of rapid diversification into multiple species. Gradual environmental changes might influence evolution over time but do not inherently lead to the rapid formation of new species. Lastly, the reappearance of an extinct species is not related to adaptive radiation; rather, it could pertain to phenomena such as de-extinction or cryptic species re-discovery.