Q.(a) Darwin's finches and Australian marsupials are suitable examples of adaptive radiation - Justify the statement. OR

Let’s start with an everyday image. Imagine a single family of musicians — say, a group of siblings who all learned the same basic instrument, the piano. Over time, one sibling moves to a jazz club and starts improvising, another joins an orchestra and plays classical concertos, a third becomes a film scorer who uses electronic keyboards, and a fourth teaches music to young children using simple, colourful pianos. They all came from the same training, but each adapted their skills to a very different environment. That is the core idea of adaptive radiation, but in biology it happens over many generations, not a single lifetime.

Adaptive radiation is the process by which a single ancestral species rapidly diversifies into many new species, each adapted to a different ecological niche. The key word is rapidly — in geological time, not human time — and the driving force is that the ancestral group encounters a variety of new environments or resources, with little competition from other species.

Think of it as an evolutionary explosion. A single species arrives on an island chain, or survives a mass extinction, and finds itself in a world of empty opportunities. Different groups within that species start using different food sources, living in different habitats, or avoiding predators in different ways. Over time, natural selection favours those variations, and the groups become so different that they can no longer interbreed — they become separate species.

The most famous example, and the one your NCERT textbook will emphasise, is Darwin’s finches on the Galápagos Islands. A single species of finch from the South American mainland colonised the islands. On different islands, with different food supplies — some with hard seeds, some with soft seeds, some with insects, some with cactus flowers — the finches evolved different beak shapes and sizes. One finch developed a thick, strong beak to crack nuts; another a slender, pointed beak to probe flowers; another a parrot-like beak to tear bark. All from one ancestor, all now distinct species.

Another classic case is the Hawaiian honeycreepers. A single finch-like ancestor colonised the Hawaiian islands and, over millions of years, gave rise to over 50 species with beaks ranging from curved for nectar-feeding to chisel-like for wood-boring. The isolation of each island and the variety of habitats — forests, mountains, coasts — drove the radiation. …