Define adaptive radiation and name a mammal example.

• A. Rapid diversification of a lineage into many forms occupying different niches; example: after the dinosaurs' extinction, placental mammals diversified into many lineages (bats, primates, cetaceans).
• B. Evolution of traits due to random genetic drift with no selective pressure.
• C. Convergent evolution where unrelated groups develop similar features.
• D. A single lineage spreading into new geographic areas.

Answer: (D)

Adaptive radiation is a rapid diversification of a lineage into many forms occupying different ecological niches. After the dinosaurs went extinct, placental mammals diversified quickly into multiple lineages, giving rise to bats, primates, whales and dolphins, and many other forms that filled a variety of lifestyles. This shows how one ancestral group can branch into distinct species each adapted to a different way of life. The other options describe different evolutionary ideas: random genetic drift with no selective pressure doesn’t drive niche diversification; convergent evolution is unrelated groups evolving similar traits independently; and simply spreading into new geographic areas isn’t enough to capture the rapid niche-focused diversification seen in adaptive radiation. A clear mammal example of this process is the emergence of diverse placental lineages such as bats and cetaceans.