Example of adaptive radiation besides Darwin's finches.

Example of adaptive radiation besides Darwin's finches.

• A. Darwin's finches or Hawaiian honeycreepers
• B. A population maintaining the same trait frequencies
• C. A pathogen evolving within a host without speciation
• D. Genetic drift causing random fixation of alleles without new species

Answer: (A)

Adaptive radiation happens when one ancestral species rapidly diversifies into many species that each occupy a different ecological niche. The Hawaiian honeycreepers exemplify this pattern: they descended from a single, relatively generic finch-like ancestor and radiated into numerous species across the Hawaiian Islands, with beak shapes and sizes specialized for a variety of foods—nectar, insects, seeds, fruit, and more. This kind of diversification is driven by geographic isolation and the availability of diverse resources, which together allow different populations to adapt in different directions and become distinct species. Other scenarios describe stable trait frequencies, evolution within a host without leading to new species, or random genetic drift fixing alleles without producing new species. These do not involve the lineage splitting and niche-driven diversification that characterizes adaptive radiation.

Adaptive radiation happens when one ancestral species rapidly diversifies into many species that each occupy a different ecological niche. The Hawaiian honeycreepers exemplify this pattern: they descended from a single, relatively generic finch-like ancestor and radiated into numerous species across the Hawaiian Islands, with beak shapes and sizes specialized for a variety of foods—nectar, insects, seeds, fruit, and more. This kind of diversification is driven by geographic isolation and the availability of diverse resources, which together allow different populations to adapt in different directions and become distinct species.

Other scenarios describe stable trait frequencies, evolution within a host without leading to new species, or random genetic drift fixing alleles without producing new species. These do not involve the lineage splitting and niche-driven diversification that characterizes adaptive radiation.