Adaptive radiation occurs when one ancestral species rapidly produces many descendant species adapted to different habitats or ecological roles.
The process is especially likely when organisms encounter many open niches, face limited competition, or become geographically isolated. Descendant populations accumulate different adaptations as they exploit separate resources or environments. Over time, reproductive barriers can develop and the populations can become distinct species.
Darwin’s finches in the Galápagos are a famous example. Molecular and anatomical evidence indicates that several finch species descended from a common ancestral colonist and later evolved different beaks and feeding habits. The Hawaiian honeycreepers provide another well-known example of island diversification.
Adaptive radiation is broader than simply having many related species. The defining feature is diversification linked to ecological opportunity and specialization, not merely a large family tree.