What Is Adaptive Radiation

• Adaptive radiation refers to the process where organisms diversify rapidly into a variety of forms, typically when they occupy different ecological niches.
• Darwin's finches (Option B): These finches are a classic example of adaptive radiation. Over time, they evolved different beak shapes to exploit different food sources on the Galápagos Islands.
• Australian marsupials (Option C): Marsupials in Australia (such as kangaroos, koalas, and wombats) evolved through adaptive radiation to fill various ecological niches.
• Placental mammals (Option D): Placental mammals represent a major group of mammals that have diversified through adaptive radiation, evolving various forms to adapt to different environments.
• Long-necked Giraffe (Option A): While the long neck of giraffes is an adaptation to feeding on high tree branches, it does not represent adaptive radiation. The long neck evolved in a specific environment and does not demonstrate the broad diversification of species seen in true adaptive radiation events.

The correct answer is (A) : Long-necked Giraffe.