NCERT Solutions for Class 12 Biology Chapter 6: Evolution (NCERT 2026–27)

Q: What is Class 12 Biology Chapter 6 Evolution about?

Chapter 6 covers the origin of life (Big Bang, chemical evolution, Miller's experiment), theories of evolution by natural selection (Darwin and Wallace), evidences for evolution, adaptive radiation, the mechanisms of evolution, the Hardy-Weinberg principle, a brief account of the evolution of life forms, and the origin and evolution of man.

Q: How many exercise questions are there in Class 12 Biology Chapter 6?

The NCERT Exercises for Evolution has 10 questions. Several are open-ended find out / trace / practise activities; all are reproduced verbatim and answered with model solutions on this page.

Q: What is the Hardy-Weinberg principle formula?

For two alleles A (p) and a (q): p + q = 1 and p^2 + 2pq + q^2 = 1, where p^2 = frequency of AA, 2pq = Aa and q^2 = aa. Allele frequencies stay constant unless gene flow, genetic drift, mutation, recombination or natural selection disturb the equilibrium.

Q: Are these Class 12 Biology Chapter 6 solutions free?

Yes. All ClearStudy NCERT Solutions for Class 12 Biology are free and follow the official NCERT textbook for session 2026-27.

These Class 12 Biology Chapter 6 solutions cover Evolution in full — the origin of life, theories of evolution, evidences (paleontological, embryological, anatomical, biochemical), adaptive radiation, the mechanism of evolution and the Hardy–Weinberg principle with fully worked numericals. Every NCERT “Exercises” question is reproduced verbatim and answered in exam-ready style for session 2026–27.

Class: 12 Subject: Biology Chapter: 6 Chapter name: Evolution Exercises: 10 questions Session: 2026–27

On this page

Chapter overview
Key concepts & definitions
Hardy–Weinberg principle (with formula)
NCERT Exercises — solutions
Extra practice questions
MCQs & Assertion–Reason
Common mistakes & exam tips
FAQs

Class 12 Biology Chapter 6 Solutions – Overview

Chapter 6, Evolution, traces the story of life from the origin of the universe to the evolution of modern humans. It begins with the Big Bang theory and the formation of the Earth (about 4.5 billion years ago), then discusses the origin of life — panspermia, the discredited theory of spontaneous generation (disproved by Louis Pasteur), and the Oparin–Haldane idea of chemical evolution confirmed by the Miller–Urey experiment. It then explains the theory of evolution by natural selection (Darwin and Wallace), the many evidences for evolution, adaptive radiation, the mechanisms driving evolution (mutation, recombination, gene flow, genetic drift and natural selection), the algebraic Hardy–Weinberg principle of genetic equilibrium, a brief account of the evolution of life forms across geological time, and finally the origin and evolution of man.

Key Concepts & Definitions

Chemical evolution: the formation of diverse organic molecules (amino acids, sugars, nitrogen bases) from inorganic constituents under early-Earth conditions, preceding the first cellular life.

Oparin–Haldane hypothesis: the first life arose from pre-existing non-living organic molecules (e.g., RNA, protein); supported by the Miller–Urey experiment (1953), in which electric discharge through CH₄, H₂, NH₃ and water vapour produced amino acids.

Natural selection: the mechanism (Darwin) by which individuals better fit for their environment leave more progeny; fitness here means reproductive fitness.

Homologous organs: structurally similar organs with a common ancestral origin but different functions (e.g., forelimbs of whale, bat, cheetah, human) — evidence of divergent evolution.

Analogous organs: structurally different organs performing similar functions (e.g., wings of butterfly and bird; eyes of octopus and mammal) — result of convergent evolution.

Adaptive radiation: evolution of different species from a point of origin, radiating to different habitats in a geographical area (e.g., Darwin’s finches; Australian marsupials).

Genetic drift: change in allele frequency by chance; the founder effect occurs when a drifted population becomes so different that it forms a new species.

Hardy–Weinberg Principle — Formula & Worked Method

The Hardy–Weinberg principle states that allele frequencies in a population are stable and remain constant from generation to generation in the absence of disturbing factors. The gene pool stays constant — this is genetic equilibrium. The sum of all allelic frequencies is 1.

For a gene with two alleles A (frequency p) and a (frequency q):

p + q = 1

p² + 2pq + q² = 1

where p² = frequency of homozygous dominant (AA), 2pq = frequency of heterozygotes (Aa), and q² = frequency of homozygous recessive (aa). This is the binomial expansion of (p + q)².

Five factors disturb this equilibrium and so cause evolution: gene flow (migration), genetic drift, mutation, genetic recombination and natural selection. When the measured frequency differs from the expected, the difference indicates the extent of evolutionary change.

NCERT Exercises — Solutions

All questions below are reproduced verbatim from the NCERT textbook (Reprint 2026–27). Several are open-ended “find out / practise / trace” activities; model answers and worked guidance are given for each.

1. Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.

ANSWER A bacterial population has built-in (pre-existing) variation: due to chance mutation, a few individuals already carry genes that make them resistant to a particular antibiotic, while most are sensitive. When the antibiotic is applied, it acts as a selection pressure. The sensitive bacteria are killed, but the rare resistant individuals survive — they are the “fittest” under these new conditions. The surviving resistant bacteria reproduce (and bacteria divide very rapidly), passing on the resistance gene. Within a few generations the entire population becomes resistant. This is exactly Darwinian natural selection: heritable variation + differential survival + greater reproduction of the fit. Because the bacterial life span is short, evolution that would take millions of years in larger animals is seen here within months or years — an example of evolution by anthropogenic action.

2. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.

ANSWER (model / activity) This is an information-gathering activity. Examples you may report from reliable sources: the discovery of Tiktaalik (a “fishapod” transitional form between fish and tetrapods), feathered dinosaur fossils from China linking dinosaurs and birds, Homo naledi and the “Hobbit” Homo floresiensis among human ancestors, and Ambulocetus as a walking-whale link. A long-standing “controversy” is the debate between gradualism (Darwin’s slow change) and punctuated equilibrium (long stable periods broken by rapid change). The science-vs-special-creation debate is also frequently reported. Cite the newspaper / article you used. (Any well-sourced, recent example is accepted.)

3. Attempt giving a clear definition of the term species.

ANSWER A species is a group of organisms that resemble one another in their structural and functional features and are capable of interbreeding among themselves to produce fertile offspring, but are reproductively isolated from members of other species. In short (Biological Species Concept): a species is a natural population of actually or potentially interbreeding individuals that are reproductively isolated from other such groups.

4. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)

ANSWER The major components changed together through these stages:

Stage	Time	Brain (cc)	Posture / skeleton & diet
Dryopithecus & Ramapithecus	~15 mya	ape-like	Hairy, walked like gorillas/chimps; Ramapithecus more man-like
Australopithecus	~2 mya	small	Walked upright (< 4 ft); hunted with stone weapons but mainly ate fruit
Homo habilis	~2 mya	650–800	First hominid; probably did not eat meat
Homo erectus	~1.5 mya	~900	Larger brain; probably ate meat
Neanderthal man	1,00,000–40,000 yrs	1400	Used hides to cover body; buried their dead
Homo sapiens	75,000–10,000 yrs	~1350–1400	Arose in Africa, spread across continents; cave art ~18,000 yrs; agriculture ~10,000 yrs

Thus human evolution shows a steady increase in brain size and function, a shift to erect bipedal posture with a modified skeleton (pelvis, foot, skull), and a change in diet from largely fruit-eating to mixed/meat-eating, alongside tool use, language and self-consciousness.

5. Find out through internet and popular science articles whether animals other than man has self-consciousness.

ANSWER (model / activity) Yes — evidence suggests several animals show signs of self-consciousness. The classic test is the mirror self-recognition (MSR) test: an animal that recognises a mark on its own body seen in a mirror is taken to have a sense of self. Animals that have passed mirror or related tests include great apes (chimpanzees, orangutans, gorillas, bonobos), dolphins, elephants, and some birds (magpies). They also show problem-solving, planning and emotional behaviour. However, the matter is still debated, since the mirror test may not be valid for animals that rely more on smell or sound than sight. (Cite the source you used.)

6. List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.

ANSWER (model / activity)

#	Modern-day animal	Linked ancient fossil / ancestor
1	Horse	Eohippus (Hyracotherium)
2	Elephant	Moeritherium
3	Bird (e.g., crow)	Archaeopteryx
4	Whale	Ambulocetus / Basilosaurus
5	Human (Homo sapiens)	Homo erectus / Australopithecus
6	Crocodile	Phytosaurs (archosaur relatives)
7	Camel	Protylopus
8	Lungfish / amphibians	Coelacanth (lobefin, “living fossil”)
9	Tortoise / turtle	Proganochelys
10	Dog (and other carnivores)	Miacis

(Any valid, well-sourced modern-fossil pairs are accepted.)

7. Practise drawing various animals and plants.

ANSWER (activity) This is a practical drawing exercise to be done in your notebook. Practise neat, labelled sketches of forms mentioned in the chapter — Darwin’s finches with different beaks, homologous forelimbs of whale/bat/cheetah/human, the family tree of dinosaurs, and the evolutionary sketch of plant forms across geological periods. Clear, labelled diagrams help in scoring full marks in the board exam.

8. Describe one example of adaptive radiation.

ANSWER Darwin’s finches of the Galapagos Islands are the classic example. Darwin observed many varieties of small black birds (finches) on the islands. He concluded that all of them evolved on the islands from a single ancestral seed-eating stock. From the original seed-eating form, finches with altered beaks arose — some became insectivorous and others vegetarian — each adapted to a different food source and habitat. This process, where many different species evolve from a point of origin and radiate to different geographical areas/habitats, is called adaptive radiation. (Australian marsupials are another valid example.)

9. Can we call human evolution as adaptive radiation?

ANSWER No. Adaptive radiation means many different species evolving from a single ancestral stock within a geographical area, each adapting to a different habitat (as in Darwin’s finches or Australian marsupials). Human evolution does not fit this pattern. It is a gradual, more or less linear (anagenetic) sequence of forms — Australopithecus → Homo habilis → Homo erectus → Neanderthal → Homo sapiens — leading to a single surviving species rather than a fan of many species radiating into different niches. Hence human evolution is not an example of adaptive radiation.

10. Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.

ANSWER (horse, Equus) The evolution of the horse is one of the best-documented fossil sequences, showing a steady increase in body size, lengthening of limbs, reduction of side toes to a single hoof, and lengthening of the teeth for grazing:

Stage	Approx. period	Key features
Eohippus (Hyracotherium)	Eocene	Small (fox-sized); 4 toes on forelimb, 3 on hind; short teeth; browser
Mesohippus	Oligocene	Larger; 3 toes on each foot, middle toe dominant
Merychippus	Miocene	Still 3 toes but stood mainly on the middle toe; longer teeth; grazer
Pliohippus	Pliocene	Larger; effectively one functional toe with splints of side toes
Equus	Recent	Modern horse; single hoofed toe; long limbs; high-crowned grazing teeth

Overall trend: increase in size, single-toed hoofed limb for fast running on grasslands, and teeth adapted from browsing soft leaves to grazing tough grass. (Trace any one animal of your choice with teacher’s guidance.)

Extra Practice Questions

Short Answer Type Questions

Q1. State the Hardy–Weinberg principle.

ANSWERIt states that allele frequencies in a population are stable and remain constant from generation to generation (genetic equilibrium) when no evolutionary forces act; the gene pool stays constant and the sum of allelic frequencies equals 1, expressed as p² + 2pq + q² = 1.

Q2. Worked numerical — In a population, the frequency of the recessive allele (a) is q = 0.3. Find the frequencies of AA, Aa and aa genotypes.

ANSWER Given q = 0.3, so p = 1 − q = 1 − 0.3 = 0.7.

AA = p² = (0.7)² = 0.49

Aa = 2pq = 2 × 0.7 × 0.3 = 0.42

aa = q² = (0.3)² = 0.09

Check: 0.49 + 0.42 + 0.09 = 1.00. So 49% AA, 42% Aa and 9% aa.

Q3. Worked numerical — In a population of 1000 people, 360 show the recessive trait (aa). Find the allele frequencies p and q, and the number of carriers (Aa).

ANSWER Frequency of aa = q² = 360/1000 = 0.36.

q = √0.36 = 0.6, p = 1 − 0.6 = 0.4

Aa = 2pq = 2 × 0.4 × 0.6 = 0.48

Number of carriers = 0.48 × 1000 = 480 individuals. (AA = p² = 0.16 → 160; check: 160 + 480 + 360 = 1000.)

Q4. Differentiate between homologous and analogous organs with one example each.

ANSWERHomologous organs have the same basic structure and common ancestry but different functions, showing divergent evolution — e.g., forelimbs of human and whale. Analogous organs have different structure but similar function, showing convergent evolution — e.g., wings of a butterfly and a bird.

Q5. What was the Miller–Urey experiment and what did it prove?

ANSWERS. L. Miller (1953) created early-Earth conditions in a closed flask by passing electric discharge through a mixture of CH₄, H₂, NH₃ and water vapour at about 800°C. He obtained amino acids. This supported the Oparin–Haldane idea of chemical evolution — that organic molecules of life could form from inorganic constituents under early-Earth conditions.

Long Answer Type Questions

Q1. Describe the various evidences that support organic evolution.

ANSWER(i) Paleontological evidence (fossils): fossils in different sedimentary layers show that life forms varied over time and that new forms arose at different periods — radioactive dating gives their ages. (ii) Embryological evidence: embryos of all vertebrates share features (e.g., vestigial gill slits) — though von Baer corrected Haeckel’s overstatement that embryos pass through adult stages of ancestors. (iii) Comparative anatomy & morphology: homologous organs (forelimbs of mammals; thorns and tendrils of Bougainvillea/Cucurbita) show divergent evolution and common ancestry, while analogous organs (wings of birds and insects) show convergent evolution. (iv) Biochemical evidence: similarities in proteins and genes performing the same function in diverse organisms point to common ancestry. (v) Evidence from artificial selection and natural selection in action: man has produced many breeds (dogs) in a few centuries; the industrial melanism of peppered moths in England and the rapid rise of antibiotic/pesticide resistance demonstrate natural selection occurring in observable time.

Q2. Explain the mechanism of evolution and the factors that disturb Hardy–Weinberg equilibrium.

ANSWERVariation arises mainly through mutation (Hugo de Vries called large sudden mutations “saltation”) and genetic recombination during gametogenesis. Such variations, coupled with reproductive success, change allele frequencies. The Hardy–Weinberg principle says allele frequencies stay constant unless disturbed; five factors disturb this equilibrium and cause evolution: gene flow (migration) — movement of alleles between populations; genetic drift — random change in allele frequency, which can cause the founder effect; mutation — source of new alleles; genetic recombination; and natural selection — differential survival and reproduction of heritable variants, leading to stabilising, directional or disruptive change. When the observed frequency differs from the expected (p² + 2pq + q² = 1), it measures the extent of evolutionary change.

Q3. Compare the theories of Lamarck and Darwin regarding evolution.

ANSWERLamarck (use and disuse / inheritance of acquired characters): organs used more develop and those unused degenerate, and these acquired characters are inherited — e.g., giraffes elongated their necks by stretching to reach high leaves and passed this on. This conjecture is no longer accepted, because acquired (somatic) characters are not heritable. Darwin (natural selection): populations have heritable variation; resources are limited so there is a struggle for existence; individuals better adapted (higher reproductive fitness) survive and leave more progeny, gradually changing the population — “survival of the fittest.” Darwin saw evolution as gradual; de Vries later argued mutations cause sudden speciation. Darwin’s theory, refined by genetics, forms the basis of modern evolutionary biology.

MCQs & Assertion–Reason

1. The Miller–Urey experiment provided evidence for:

(a) spontaneous generation (b) chemical evolution (c) panspermia (d) special creation

2. Spontaneous generation theory was disproved by:

(a) Charles Darwin (b) Louis Pasteur (c) Oparin (d) Hugo de Vries

3. Forelimbs of whale, bat and human are an example of:

(a) analogous organs (b) vestigial organs (c) homologous organs (d) convergent evolution

4. Wings of a butterfly and a bird are:

(a) homologous — divergent evolution (b) analogous — convergent evolution (c) vestigial (d) identical in structure

5. Darwin’s finches of the Galapagos Islands are a classic example of:

(a) convergent evolution (b) genetic drift (c) adaptive radiation (d) saltation

6. According to Hardy–Weinberg, the frequency of heterozygotes is given by:

(a) p² (b) q² (c) 2pq (d) p + q

7. Which of the following is NOT a factor affecting Hardy–Weinberg equilibrium?

(a) gene flow (b) genetic drift (c) random mating in a large population (d) natural selection

8. The idea that mutations (large, sudden changes) cause evolution was proposed by:

(a) Lamarck (b) Hugo de Vries (c) Wallace (d) Haldane

9. The brain capacity of Homo habilis was about:

(a) 650–800 cc (b) 900 cc (c) 1400 cc (d) 100 cc

10. When a drifted small population becomes so different that it forms a new species, the effect is called:

(a) gene flow (b) founder effect (c) natural selection (d) saltation

Answer key: 1-(b), 2-(b), 3-(c), 4-(b), 5-(c), 6-(c), 7-(c), 8-(b), 9-(a), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Antibiotic resistance in bacteria supports Darwinian natural selection.

Reason: Pre-existing resistant variants survive the antibiotic and reproduce, increasing in the population.

A-R 2. Assertion: Homologous organs indicate common ancestry.

Reason: Homology is based on divergent evolution of the same basic structure for different functions.

A-R 3. Assertion: Human evolution is an example of adaptive radiation.

Reason: Many human species evolved from one ancestor, each radiating into a different habitat.

A-R 4. Assertion: In a population at Hardy–Weinberg equilibrium, allele frequencies stay constant.

Reason: Gene flow, genetic drift, mutation, recombination and natural selection are all absent.

A-R 5. Assertion: Analogous organs are the result of convergent evolution.

Reason: Different structures evolve similar functions due to similar habitats and selection pressures.

Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(A).

Common Mistakes & Exam Tips

Common mistakes to avoid

Confusing homologous (same structure, common ancestry → divergent) with analogous (same function → convergent) organs.
Calling human evolution “adaptive radiation” — it is a linear sequence, not a radiation into many species.
Forgetting that Darwinian fitness = reproductive fitness, not physical strength.
Mixing up p² (AA), 2pq (Aa) and q² (aa) in Hardy–Weinberg sums; always start from q² if the recessive count is given.
Crediting spontaneous generation — it was disproved by Pasteur.
Stating that acquired characters are inherited (Lamarck) — this is no longer accepted.

How to score full marks in this chapter

Learn the Hardy–Weinberg equation and practise numericals: from any one known frequency you can find all others (p + q = 1). For “evidence for evolution” answers, list the five categories (paleontological, embryological, anatomical, biochemical, observed selection) with one example each. Remember key brain sizes (Homo habilis 650–800 cc, Homo erectus 900 cc, Neanderthal 1400 cc) and the five factors that disturb genetic equilibrium. Use neat labelled diagrams for finches, homologous forelimbs and horse evolution.

Frequently Asked Questions

What is Class 12 Biology Chapter 6 Evolution about?

Chapter 6 covers the origin of life (Big Bang, chemical evolution, Miller’s experiment), theories of evolution by natural selection (Darwin and Wallace), evidences for evolution, adaptive radiation, the mechanisms of evolution, the Hardy–Weinberg principle, a brief account of the evolution of life forms, and the origin and evolution of man.

How many exercise questions are there in Class 12 Biology Chapter 6?

The NCERT “Exercises” for Evolution has 10 questions. Several are open-ended “find out / trace / practise” activities; all are reproduced verbatim and answered with model solutions on this page.

What is the Hardy–Weinberg principle formula?

For two alleles A (p) and a (q): p + q = 1 and p² + 2pq + q² = 1, where p² = frequency of AA, 2pq = Aa and q² = aa. Allele frequencies stay constant unless gene flow, genetic drift, mutation, recombination or natural selection disturb the equilibrium.

Are these Class 12 Biology Chapter 6 solutions free?

Yes. All solutions are free and follow the official NCERT Biology textbook for session 2026–27.

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