Q.Two organisms occupying a particular geographical area (say desert) show similar adaptive strategies. Taking examples, describe the phenomenon.
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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. …
This phenomenon is called convergent evolution — unrelated organisms, with no recent common ancestor, independently evolve similar structures or strategies because they face the same kind of environmental pressure.
The question's own hint — "a particular geographical area, say desert" — points to the classic textbook example: cacti (family Cactaceae, native to the deserts of the Americas) and Euphorbia species (family Euphorbiaceae, native to the deserts of Africa) belong to entirely different, distantly related plant families, yet both have independently evolved thick, fleshy, water-storing stems; leaves reduced to spines (cutting the surface area lost to transpiration); and stems that have taken over the leaf's normal photosynthetic role. Neither family inherited these traits from a shared desert-adapted ancestor — each arrived at the same solution separately because deserts impose the identical challenge (survive on very little water) regardless of which lineage happens to live there. …
This is convergent evolution — the desert environment forces two unrelated plant lineages, cacti and Euphorbia, to independently evolve near-identical water-conserving body forms (fleshy stems, reduced spine-like leaves) despite sharing no recent common ancestor.
When two organisms living in the same type of habitat show similar adaptive strategies despite not being closely related, biologists call this convergent evolution — evolution converging on the same solution from different starting points, because the same environmental problem imposes the same selective pressure on whichever lineage happens to occupy that habitat.
Desert plants are the textbook case for this. A desert imposes one dominant challenge on any plant living there: survive on very little water while tolerating intense heat and radiation. Two plant families that are not closely related have each solved this problem in essentially the same way:
- Cacti (family Cactaceae), native to the deserts of the Americas, have thick, fleshy, water-storing stems; their leaves are reduced to spines, cutting the surface area available for water loss; and the stem itself has taken over the plant's photosynthesis.
- Euphorbia species (family Euphorbiaceae), native to the deserts of Africa, independently show the very same fleshy, water-storing stem, the same reduction of leaves to spines, and the same shift of photosynthesis onto the stem.
These two families share no close common ancestor — whatever ancestor they do share long predates either lineage evolving succulence. Neither "borrowed" the trait from the other; instead, the desert environment itself selected for the same combination of features in both lineages independently, because any variant that stored water and minimised its transpiring surface had a survival advantage in that specific habitat, regardless of its ancestry. …
Identify the shared environmental pressure first (desert = extreme water scarcity), then ask what structural solution any organism would need regardless of ancestry (water storage, minimised transpiring surface) — this predicts the cactus/Eu …
- TG EAPCET 2026Set ap-2026-05-04-AN1 markMCQQ.Consider the following statements Statement I: In human beings, trachea and oesophagus open into the larynx Statement II: Human dentition is pleurodont and polyphyodont type The correct answer is Options : (A) Both statement I and statement II are true (B) Both statement I and statement II are false (C) Statement I is true, but statement II is false (D) Statement I is false, but statement II is true
›Reveal solutionSolution
The trachea and oesophagus do not both open into the larynx — only the trachea does; human dentition is thecodont and diphyodont, not pleurodont and polyphyodont. So both statements are false.
The question tests two distinct pieces of human anatomy and dental biology. Let’s take each statement apart, understand the correct facts, and then see why both are wrong.
Statement I: “In human beings, trachea and oesophagus open into the larynx”
The larynx is the voice box, located at the top of the trachea (windpipe). It is part of the respiratory system. The trachea begins at the larynx and carries air to the lungs. The oesophagus, on the other hand, is a muscular tube that carries food from the pharynx to the stomach — it lies behind the trachea and is part of the digestive system.
The key point: the larynx opens only into the trachea. The oesophagus does not open into the larynx. Instead, both the trachea and oesophagus open into the pharynx (the common passage for air and food at the back of the throat). The epiglottis, a flap of cartilage, covers the laryngeal opening during swallowing to prevent food from entering the trachea.
So Statement I is false.
Statement II: “Human dentition is pleurodont and polyphyodont type”
Let’s decode these terms:
- Pleurodont: teeth are attached to the side (inner surface) of the jawbone, not in sockets. This is seen in many reptiles (e.g., lizards). Humans have thecodont dentition — teeth are embedded in sockets (alveoli) of the jawbone. …
- TG EAPCET 2025Set ap-2025-04-29-FN1 markMCQQ.Study the following and choose the correct statements: I. Darwinism explains the survival of the fittest but not the arrival of the fittest II. Mutations are subjected to natural selection III. Hardy – Weinberg equilibrium is applicable to small populations IV. Industrial melanism was best studied in \textit{Drosophila melanogaster} (A) I, III (B) II, IV (C) I, II (D) III, IV
›Reveal solutionSolution
Statements I and II are correct: Darwinism explains the differential survival of existing variations but not their origin, and mutations provide the raw material upon which natural selection acts. The correct option is (C).
The question asks us to evaluate four statements related to evolutionary biology. To do this, we need a clear understanding of key concepts like Darwinism, natural selection, mutations, Hardy-Weinberg equilibrium, and industrial melanism. Each statement touches upon a specific aspect of these theories or phenomena.
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Evaluate Statement I: Darwinism explains the survival of the fittest but not the arrival of the fittest.
- Darwin's theory of natural selection, often summarized as "survival of the fittest," explains how individuals with advantageous traits are more likely to survive, reproduce, and pass on those traits to their offspring. This leads to a gradual change in the population over generations.
- However, Darwin's theory did not fully explain the origin of these variations or "fittest" traits. He observed variation but did not know the genetic mechanisms behind it. The source of new variations (mutations and genetic recombination) was discovered later, forming part of the modern synthesis of evolution.
- Therefore, Darwinism explains which individuals survive and reproduce based on existing traits (survival of the fittest), but not how those novel traits initially arise (arrival of the fittest).
- This statement is correct.
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Evaluate Statement II: Mutations are subjected to natural selection.
- Mutations are random changes in the DNA sequence. These changes introduce new alleles into a population, which can lead to new traits (phenotypes).
- Natural selection acts on these phenotypes. If a mutation results in a phenotype that provides a survival or reproductive advantage in a particular environment, individuals carrying that mutation are more likely to survive and pass it on. Conversely, if a mutation is deleterious, it will be selected against.
- Thus, mutations provide the raw material for evolution, and natural selection then "screens" or "subjects" these mutations, favoring beneficial ones and eliminating harmful ones.
- This statement is correct.
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Evaluate Statement III: Hardy – Weinberg equilibrium is applicable to small populations.
- The Hardy-Weinberg principle describes a theoretical state where allele and genotype frequencies in a population remain constant from generation to generation. This equilibrium holds true only under specific conditions.
- One of the crucial conditions for Hardy-Weinberg equilibrium is a very large population size. This is because in small populations, random fluctuations in allele frequencies, known as genetic drift, can have a significant impact. Genetic drift can lead to the loss or fixation of alleles purely by chance, thereby changing allele frequencies and violating the Hardy-Weinberg equilibrium.
- Therefore, Hardy-Weinberg equilibrium is not applicable to small populations.
- This statement is incorrect.
The Hardy-Weinberg equilibrium is described by the equations:
p+q=1 (allele frequencies)
p2+2pq+q2=1 (genotype frequencies) …
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- TG EAPCET 2025Set ap-2025-04-29-FN1 markMCQQ.It was more man like (A) Ramapithecus (B) Dryopithecus (C) Australopithecus (D) Macaca
›Reveal solutionSolution
Ramapithecus was more man-like; Dryopithecus was more ape-like.
In the standard account of human evolution, two early ape-like forms are compared: Dryopithecus, which was more ape-like, and Ramapithecus, which was more man-like (it was hairy and walked like gorillas and chimpanzees, but showed more human affinities in its dentition and jaw). …
- TG EAPCET 2024Set ap-2024-05-08-FN1 markMCQQ.If one species diverges to become two or more species, it is called (A) Cladogenesis (B) Anagenesis (C) Phyletic evolution (D) Convergent evolution
›Reveal solutionSolution
When one species splits into two or more distinct species, it is called cladogenesis, which increases the number of species. The correct option is (A).
The question asks for the term describing the process where one species diverges to become two or more species. This phenomenon is a fundamental aspect of evolution known as speciation, specifically referring to the branching pattern of evolution. Understanding the different modes of speciation and evolutionary patterns is key here.
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Understanding Speciation:
Speciation is the evolutionary process by which new biological species arise from existing ones. There are primarily two ways this can occur in terms of lineage patterns:
- Branching (Divergent) Evolution: An ancestral species splits into two or more distinct daughter species. This increases the total number of species.
- Non-branching (Linear) Evolution: An ancestral species gradually transforms over time into a new species without splitting. The original species is replaced by the new one.
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Analyzing the Options:
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(A) Cladogenesis:
Cladogenesis refers to the evolutionary process where an ancestral species splits into two or more new species. This is a branching event in the phylogenetic tree, leading to an increase in biodiversity. The term "clade" refers to a group of organisms that includes an ancestor and all of its descendants. When one species diverges to become two or more, it forms new clades. This directly matches the description in the question.
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(B) Anagenesis:
Anagenesis (also known as phyletic gradualism or phyletic evolution) describes the evolutionary change within a single lineage over time. In anagenesis, an ancestral species gradually transforms into a new species without any branching or splitting. The original species is replaced by the new one. This process does not increase the number of species; it simply changes one species into another over a long period. Therefore, it does not fit the description of one species diverging into two or more.
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(C) Phyletic evolution: …
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- TG EAPCET 2023Set ap-2023-05-10-AN1 markMCQQ.In this type of interspecific interactions the organisms are involved in co-evolution (A) Mutualism (B) Commensalism (C) Predation (D) Competition
›Reveal solutionSolution
Co-evolution—where two species reciprocally shape each other's evolution over time—occurs most strongly in mutualism, where both partners exert selective pressure on one another. The answer is (A).
Co-evolution describes the phenomenon where two or more species evolve in response to each other, each acting as a selective pressure on the other. For this to happen, the interaction must be tight enough and persistent enough that changes in one species favor corresponding changes in the other, generation after generation.
Mutualism creates exactly this dynamic. When two species depend on each other for survival or reproduction, any trait in species A that better serves species B will be favored, and vice versa. The classic examples make this clear: flowering plants and their pollinators have co-evolved elaborate matching traits—flower shape, color, nectar composition on one side; tongue length, sensory abilities, feeding behavior on the other. Neither evolves in isolation; each is both sculptor and clay.
Let me walk through why the other interactions don't typically drive co-evolution as strongly:
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Commensalism involves one species benefiting while the other is unaffected. If species B truly experiences no cost or benefit from species A, there is no selective pressure on B to evolve in response to A. Co-evolution requires reciprocal pressure, which commensalism lacks by definition.
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Predation can involve co-evolution (the classic predator-prey arms race), but the question asks which interaction characteristically involves co-evolution. Predation often shows it, but many predator-prey systems are quite loose—generalist predators feeding on many prey species, for instance, dilute the selective pressure any one prey exerts. …
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- TG EAPCET 2023Set ap-2023-05-11-FN1 markMCQQ.The principle which states that the allelic frequencies in the population will remain constant from generation to generation under certain conditions was proposed by (A) Alfred Russel Wallace (B) Hardy, Weinberg (C) Sewall wright (D) Thomas Malthus
›Reveal solutionSolution
The principle that allelic frequencies remain constant across generations under ideal conditions is the Hardy–Weinberg principle, proposed independently by G. H. Hardy and Wilhelm Weinberg. The correct option is (B).
The question asks you to recall who proposed the fundamental population‑genetics law that says allele and genotype frequencies in a large, randomly‑mating population do not change from generation to generation unless evolutionary forces (mutation, selection, gene flow, genetic drift) act. This is the Hardy–Weinberg equilibrium.
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Why the other names don’t fit
- Alfred Russel Wallace co‑developed the theory of natural selection with Darwin, but he did not work on population allele frequencies.
- Sewall Wright was a major figure in population genetics (he contributed the concept of genetic drift and the F‑statistics), but the constant‑frequency principle itself was not his proposal.
- Thomas Malthus wrote about population growth and resource limits, which influenced Darwin and Wallace, but he never formulated any genetic equilibrium.
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The correct pair …
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