Adaptive radiation refers to the evolution of different species from a common ancestor. It is a process by which a single ancestral species evolves into an array of different species that are adapted to various ecological niches. This phenomenon is primarily driven by natural selection, as different populations of the same species face different environmental conditions and selective pressures.

Process of Adaptive Radiation:
- Common Ancestor: Adaptive radiation begins with a single ancestral species that colonizes a new and diverse environment. This ancestral species possesses a set of traits that allow it to survive and reproduce in its original habitat.
- Environmental Changes: Over time, the environment changes, presenting new challenges and opportunities for the ancestral species.
- Geographical Isolation: Sometimes, the ancestral species may become geographically isolated into separate populations due to factors such as the formation of barriers like mountains or rivers. This isolation prevents gene flow between populations, allowing them to undergo independent evolutionary changes.
- Natural Selection: Each population faces different selective pressures in their respective environments. Individuals with traits that increase their survival and reproductive success in their specific habitats are more likely to pass on these advantageous traits to future generations.
- Divergence: As each population adapts to its specific environment, genetic and phenotypic differences accumulate. Over time, these differences become significant enough that the populations can no longer interbreed, leading to the formation of distinct species.
- Ecological Niches: The new species occupy different ecological niches, which are specific roles and positions within their respective ecosystems. Each species has its own unique set of adaptations that allow it to exploit a particular resource or habitat.
- Increased Diversity: Through this process, a single ancestral species can give rise to multiple species, each specialized for a specific ecological niche. This leads to an increase in biodiversity within a given ecosystem.

Example:
An example of adaptive radiation is the finches found in the Galapagos Islands. These finches are believed to have descended from a common ancestor that arrived on the islands. Each finch species has a unique beak shape and size, allowing them to utilize different food sources. This diversification of beak morphology is a result of natural selection acting on the finches as they adapted to the various food resources available on the islands.

In conclusion, adaptive radiation refers to the evolution of different species from a common ancestor in response to different environmental conditions. It is a process that leads to the diversification of species and the occupation of distinct ecological niches.