Q.Distinguish between homologous and analogous organs with examples.
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Adaptive Radiation
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.
Adaptive radiation is not just any diversification. It requires three conditions:
- A single ancestral species.
- New ecological opportunities (e.g., islands, post-extinction vacancies, new key adaptations).
- Rapid speciation into forms that occupy different niches.
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. …
Homologous organs share structure/origin but differ in function (divergent evolution); analogous organs differ in structure/origin but share function (convergent evolution).
Comparative anatomy provides evidence for evolution through two kinds of organs (Evolution, NCERT Class 12 Biology):
| Feature | Homologous organs | Analogous organs |
|---|---|---|
| Basic structure | Same (built on a common plan) | Different |
| Origin (embryonic) | Same | Different |
| Function | Different | Same |
| Evolution shown | Divergent (common ancestor, adapted differently) | Convergent (unrelated ancestors, similar adaptation) |
| Example | Forelimbs of man, whale, bat and cheetah — same bones (humerus, radius-ulna, carpals) used for grasping, swimming, flying, running | Wings of a butterfly and a bird; eye of octopus and mammal; flippers of penguin and dolphin |
| … |
Showing the 12 most recent of 14 on this concept.
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: When more than one adaptive radiation have occurred in an isolated geographical area, this is called as ______ evolution.
›Reveal solutionSolution
When more than one adaptive radiation occurs independently within the same isolated geographical area, giving structurally similar (analogous) end forms, it is termed convergent evolution.
Adaptive radiation is the evolution of different species from a common ancestor within one geographical area, each adapting to a different niche (e.g., Darwin's finches on the Galapagos). When such radiation happens more than once, independently, within one isolated area, producing organisms of different ancestry that come to resemble each other in form due to simi …
- CBSE 2026Set ANNUAL1 markMCQQ.Darwin observed different types of beaks in finches adapted to different feeding habits on the Galapagos Islands. This diversity provides evidence for :(a) intraspecific competition.(b) interspecific competition.(c) origin of species by natural selection.(d) origin of species by mutation.
›Reveal solutionSolution
Darwin's finches show a variety of beak shapes evolved from one ancestral stock to suit different foods — evidence for origin of species by natural selection (adaptive radiation), so (c) is correct.
In the CBSE/NCERT Evolution chapter, Darwin observed many finch species on the Galapagos Islands. From an original seed-eating ancestor, populations diversified into forms with different beaks suited to different feeding habits (insectivorous, seed-eating, etc.). This process — many species radiating from a common ancestor into different ecological nic …
- CBSE 2025Set 57/6/11 markMCQQ.In his observations of small black birds in the Galapagos Islands, Darwin found that all the finches arose from the original ancestor : (A) Insect-eating finches (B) Seed-eating finches (C) Cactus-eating finches (D) Fruit-eating finches
›Reveal solutionSolution
Darwin's Galapagos finches all descended from an original seed-eating finch ancestor that colonized the islands and then diversified into multiple ecological niches.
When Darwin visited the Galapagos Islands during the voyage of the HMS Beagle, he encountered a remarkable group of small black birds that would later become one of the most celebrated examples of evolution in action. These finches, though superficially similar, showed striking differences in their beak shapes and sizes, each adapted to different food sources on the various islands.
The key insight Darwin eventually developed was that all these diverse finch species shared a common origin. The ancestral finch that first arrived on the Galapagos from the South American mainland was a seed-eating bird. This makes biological sense: seed-eaters are generalist feeders with robust beaks capable of handling a variety of foods, making them well-suited to colonize new, unpredictable environments.
Once established on the islands, this founding population faced a landscape rich in unexploited resources but poor in competition. Different islands offered different opportunities—some had abundant insects, others cacti, still others various seeds and fruits. Over successive generations, natural selection favored individuals whose beak shapes happened to be better suited to the locally available food. A finch with a slightly longer, more pointed beak could probe bark for insects more effectively. One with a stout, powerful beak could crack tough seeds. Another with a specialized shape could feed on cactus flowers and pulp. …
- CBSE 2025Set ANNUAL1 markMCQQ.Assertion(A): Adaptive radiation led to evolution of many varieties of finches. Reason(R): Originally finches were seed eaters.(a) Both (A) and (R) are true and (R) is the correct explanation of (A)(b) Both (A) and (R) are true but (R) is not the correct explanation of (A)(c) (A) is true but (R) is false(d) Both (A) and (R) are false
›Reveal solutionSolution
Both statements about Darwin's finches are factually true, but their original seed-eating habit does not explain why adaptive radiation happened — geographic isolation and diversification into new niches does.
Adaptive radiation is the process by which species evolve within a relatively short period of geological time from a common ancestor into a variety of forms, all adapted to different ecological niches available in a new/isolated environment, without migrating to other areas. Darwin's finches, found on the Galapagos Islands, are a classic textbook example — a single ancestral finch species, upon reaching the isolated islands, radiated into several different species, each adapted to a different food source (some seed-eating, some insect-eating, some cactus-feeding), primarily distinguished by differences in their beak shape/size suited to that specific diet.
- Assertion (A) is true — adaptive radiation did lead to the evolution of many varieties of finches. …
- CBSE 2024Set ANNUAL1 markMCQQ.Darwin's finches is an example of(a) Convergent evolution(b) Parallel evolution(c) Adaptive radiation(d) Chemical evolution
›Reveal solutionSolution
Darwin's finches are the classic textbook example of adaptive radiation — divergent evolution of many species from one ancestral form within the same isolated geographic area.
When Darwin visited the Galapagos Islands, he found many kinds of finches, differing mainly in the size and shape of their beaks, on a small isolated island. Starting from a single seed-eating ancestral finch species that colonised the islands, different populations adapted to different food sources (seeds, insects, buds, cactus flowers) available on the islands, evolving different beak shapes suited to each diet — a single ancestral species radiating into many species within one geographical …
- CBSE 2024Set ANNUAL1 markQ.Give one example of adaptive radiation.
›Reveal solutionSolution
Adaptive radiation is the evolution of many species from a common ancestor, each adapted to a different niche in the same geographic area; Darwin's finches on the Galapagos Islands are the classic example.
When a single ancestral finch species reached the isolated Galapagos Islands, it found many vacant ecological niches with no competitors. Over generations, its descendants diversified into several species differing mainly in beak size and shape, each specialised for a different food source (seed-crushing, insect-eating, cactus-feeding, etc.) - all evolving in one place from one ancestor, which is the defining feature of adaptive radiation. (Australian …
- CBSE 2023Set ANNUAL1 markQ.Where Darwin's Finches are found?
›Reveal solutionSolution
Darwin's finches inhabit the Galapagos Islands in the Pacific Ocean.
Darwin's finches are a group of about 14 closely related species of finches that Charles Darwin observed and collected during the voyage of HMS Beagle. They are found on the Galapagos Islands, a volcanic archipelago in the Pacific Ocean off the coast of Ecuador. Their varying beak shapes and sizes, adapted to differe …
- CBSE 2023Set ANNUAL1 markQ.Give an example of adaptive radiation.
›Reveal solutionSolution
Adaptive radiation is the evolution of many different species from a common ancestor, each adapted to a different niche in the same geographical area; Darwin's finches are the textbook example.
When a species colonises a new, relatively unoccupied habitat (like an island), it can diversify into multiple descendant species, each adapting to exploit a different available niche/resource — this is adaptive radiation. On the Galapagos Islands, a single ancestral finch species that arrived from the mainland diversified into more than a dozen species, differing mainly in beak size and shape, each suited to a different diet (seed- …
- CBSE 2022Set ANNUAL1 markMCQQ.Human hands, the wings of a bat, and the flippers of a seal express(a) vestigial organs(b) analogous organs(c) evolutionary organs(d) homologous organs
›Reveal solutionSolution
These forelimbs share a common structural plan, so they are homologous organs (D).
Homologous organs have the same fundamental structure and embryonic origin but perform different functions. The forelimbs of a human (grasping), a bat (flying) and a seal (swimming) are all built on the same underlying pentadactyl (five-fingered) bone arrangement — humerus, radius, ulna, carpals, metacarpals and phalanges — modified for different uses. This common ancestry with divergent function is evidenc …
- CBSE 2020Set NC1 markMCQQ.Variety of beaks of finches that Darwin found in Galapagos islands was due to(a) adaptive radiation(b) convergent evolution(c) genetic drift(d) artificial selection
›Reveal solutionSolution
Darwin's Galapagos finches diversified from a single common ancestral species into many different species, each with a beak shape adapted to exploiting a different food resource — the textbook example of adaptive radiation.
Reasoning
Adaptive radiation is the evolutionary process by which a single ancestral species, upon colonising a new, geographically isolated environment offering a variety of unoccupied ecological niches, diversifies rapidly into multiple descendant species, each becoming adapted (via natural selection) to a different niche/mode of life. Charles Darwin observed exactly this pattern among the finches of the Galapagos Islands: a single ancestral finch species that had colonised the islands diversified into many different species, each evolving a distinctly-shaped beak suited to a particular food source (e.g. seed-crushing, insect-probing, or cactus-feeding beaks) — this is the textbook illustration of adapt …
- CBSE 2019Set 57/2/11 markQ.Mention one example each from plants and animals exhibiting divergent evolution.
›Reveal solutionSolution
Divergent evolution occurs when related species adapt to different environments, developing distinct traits from a common ancestor — seen in the varied spines, tendrils and leaves of Opuntia, Bougainvillea and Cucurbita (all modified leaves), and in Darwin's finches, whose beaks diversified for different food sources across the Galápagos Islands.
Divergent evolution is the process by which organisms sharing a common ancestor evolve along separate paths, accumulating differences as they adapt to distinct ecological niches or environments. The starting point is homology — structures that are anatomically similar because they were inherited from the same ancestor, even though they may now serve entirely different functions. Over time, natural selection moulds these homologous structures in divergent directions, producing what we call adaptive radiation when the divergence is rapid and produces multiple new forms.
Plant example: Modified leaves in different species
Consider three familiar plants: Opuntia (the prickly pear cactus), Bougainvillea, and Cucurbita (the gourd family, which includes pumpkins and cucumbers). In each, the leaf has been modified to serve a completely different purpose, yet all three structures are homologous — they share the same developmental origin as foliage leaves.
- In Opuntia, leaves have become sharp spines. This adaptation reduces water loss in arid desert environments and deters herbivores from feeding on the succulent stem, which has taken over the photosynthetic role.
- In Bougainvillea, leaves have transformed into colourful bracts — the vivid pink, purple or orange structures we admire are not petals but modified leaves that attract pollinators to the small, inconspicuous flowers nestled within.
- In Cucurbita, leaves have evolved into tendrils, slender coiling structures that help the climbing vine anchor itself to supports and reach sunlight in crowded habitats.
The common ancestry is evident in the developmental blueprint, but the selective pressures of different environments — water scarcity, pollinator attraction, structural support — have driven the divergence.
Animal example: Darwin's finches
The textbook case of divergent evolution in animals comes from the finches of the Galápagos archipelago, famously studied by Charles Darwin. All the finch species on these islands descended from a common ancestral finch that arrived from the mainland. Once isolated on different islands with varying food resources, populations began to diverge. …
- CBSE 2018Set ANNUAL1 markQ.Longer toes and long prehensile tail indicate which adaptation?
›Reveal solutionSolution
Arboreal adaptation — longer, grasping toes and a long prehensile tail evolved as adaptations for gripping branches, climbing and balancing in a tree-dwelling (arboreal) habitat, characteristic of early primates.
Long grasping toes and a prehensile tail are adaptations for life in trees (arboreal habit).
Early primates evolved from ground-dwelling ancestors that took to living in trees, and their skeleton shows a suite of features suited to this arboreal lifestyle. Longer, more flexible and often opposable toes/digits give a firm grip on branches of varying thickness, while a long, muscular, prehensile tail (in New World monkeys, for example) can coil tightly around a branch, acting almost as a fifth limb for support and balance while climbing, leaping and reaching for food …
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