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Biology · Class 12 Science

Ch 6Evolution — Class 12 Biology, concept-first.

Evolutionary biology is the study of how life on Earth has changed over time. But to understand how flora and fauna have changed across millions of years, we first need the bigger context — how the Earth itself formed, how stars formed, even how the universe itself came to be.

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Key concepts

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Darwinian Natural Selection

Imagine you walk into a crowded room. Some people are naturally louder, some are quieter. Some are taller, some shorter.

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Chapter contents

The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.

Introduction

Evolutionary biology is the study of how life on Earth has changed over time. But to understand how flora and fauna have changed across millions of years, we first need the bigger context — how the Ea…

6.1

Origin of Life

When you look at a star on a clear night, you are not seeing it as it is now. The light from that star has travelled for millions of years across trillions of kilometres before reaching your eyes.

6.2

Evolution of Life Forms – A Theory

The story of evolution is not just about how life changes — it is about how we came to know that it changes at all.

6.3

What are the Evidences for Evolution?

The theory of evolution is supported by a vast body of evidence drawn from many different fields of biology.

6.4

What is Adaptive Radiation?

Adaptive radiation is the process by which a single ancestral species evolves into a diverse array of descendant species, each adapted to a different ecological niche.

6.5

Biological Evolution

Evolution by natural selection could only begin once life had a cellular basis capable of showing heritable differences in metabolism — that is, once different cells could vary in how efficiently they…

6.6

Mechanism of Evolution

Lamarck's use-and-disuse theory has an appealing simplicity, but it does not hold up: traits acquired during an individual's lifetime — such as a neck stretched by reaching for leaves — are not encode…

6.7

Hardy-Weinberg Principle

In any population, you can calculate how often a particular allele of a gene appears. The Hardy-Weinberg principle states that, under ideal conditions, these allele frequencies remain constant from on…

6.8

A Brief Account of Evolution

About 2 billion years ago, the first cellular forms of life appeared on Earth. The story of how these simple cells gave rise to the staggering diversity of plants, animals, and microbes we see today i…

6.9

Origin and Evolution of Man

The story of human evolution is pieced together from fossil evidence stretching back many millions of years.

Summary

- Origin of life: Oparin-Haldane theory proposed life arose from non-living matter via chemical evolution.

Exercises

+Show 10 questions10 questions
  1. 6.1Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.Free
  2. 6.2Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.Free
  3. 6.3Attempt giving a clear definition of the term species.Free
  4. 6.4Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)Preview
  5. 6.5Find out through internet and popular science articles whether animals other than man has self-consciousness.Preview
  6. 6.6List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.Preview
  7. 6.7Practise drawing various animals and plants.Preview
  8. 6.8Describe one example of adaptive radiation.Preview
  9. 6.9Can we call human evolution as adaptive radiation?Preview
  10. 6.10Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any…Preview

NCERT Exemplar

Higher-order thinking problems from the NCERT Exemplar.

+Show 52 questions52 questions
  1. Q1Which of the following is used as an atmospheric pollution indicator? (a) Lepidoptera (b) Lichens (c) Lycopersicon (d) LycopodiumFree
  2. Q2The theory of spontaneous generation stated that: (a) life arose from living forms only (b) life can arise from both living and non-living (…Free
  3. Q3Animal husbandry and plant breeding programmes are the examples of: (a) reverse evolution (b) artificial selection (c) mutation (d) natural…Free
  4. Q4Palaentological evidences for evolution refer to the: (a) development of embryo (b) homologous organs (c) fossils (d) analogous organs.Preview
  5. Q5The bones of forelimbs of whale, bat, cheetah and man are similar in structure, because: (a) one organism has given rise to another (b) they…Preview
  6. Q6Analogous organs arise due to: (a) divergent evolution (b) artificial selection (c) genetic drift (d) convergent evolutionPreview
  7. Q7(p+q)² = p² + 2pq + q² = 1 represents an equation used in: (a) population genetics (b) mendelian genetics (c) biometrics (d) molecular genet…Preview
  8. Q8Appearance of antibiotic-resistant bacteria is an example of: (a) adaptive radiation (b) transduction (c) pre-existing variation in the popu…Preview
  9. Q9Evolution of life shows that life forms had a trend of moving from: (a) land to water (b) dryland to wet land (c) fresh water to sea water (…Preview
  10. Q10Viviparity is considered to be more evolved because: (a) the young ones are left on their own (b) the young ones are protected by a thick sh…Preview
  11. Q11Fossils are generally found in: (a) Sedimentary rocks (b) Igneous rocks (c) Metamorphic rocks (d) Any type of rockPreview
  12. Q12For the MN-blood group system, the frequencies of M and N alleles are 0.7 and 0.3, respectively. The expected frequency of MN-blood group be…Preview
  13. Q13Which type of selection explains industrial melanism observed in moth, Biston bitularia: (a) Stabilising (b) Directional (c) Disruptive (d)…Preview
  14. Q14The most accepted line of descent in human evolution is: (a) Australopithecus → Ramapithecus → Homo sapiens → Homo habilis (b) Homo erectus…Preview
  15. Q15Which of the following is an example for link species? (a) Lobe fish (b) Dodo bird (c) Sea weed (d) ChimpanzeePreview
  16. Q16Match the scientists listed under column ‘I’ with ideas listed column ‘II’. Column I\tColumn II A. Darwin\ti. abiogenesis B. Oparin\tii. use…Preview
  17. Q17In 1953 S. L. Miller created primitive earth conditions in the laboratory and gave experimental evidence for origin of first form of life fr…Preview
  18. Q18Variations during mutations of meiotic recombinations are: (a) random and directionless (b) random and directional (c) small and directional…Preview
  19. Q19What were the characteristics of life forms that had been fossilised?Preview
  20. Q20Did aquatic life forms get fossilised? If, yes where do we come across such fossils?Preview
  21. Q21What are we referring to? When we say 'simple organisms' or 'complex organisms'.Preview
  22. Q22How do we compute the age of a living tree?Preview
  23. Q23Give an example for convergent evolution and identify the features towards which they are converging.Preview
  24. Q24How do we compute the age of a fossil?Preview
  25. Q25What is the most important pre-condition for adaptive radiation?Preview
  26. Q26How do we compute the age of a rock?Preview
  27. Q27When we talk of functional macromolecules (e.g. proteins as enzymes, hormones, receptors, antibodies etc), towards what are they evolving?Preview
  28. Q28In a certain population, the frequency of three genotypes is as follows: Genotypes: BB Bb bb frequency: 22% 62% 16% What is the likely frequ…Preview
  29. Q29Among the five factors that are known to affect Hardy-Weinberg equilibrium, three factors are gene flow, genetic drift and genetic recombina…Preview
  30. Q30What is founder effect?Preview
  31. Q31Who among the Dryopithecus and Ramapithecus was more man-like?Preview
  32. Q32By what Latin name the first hominid was known?Preview
  33. Q33Among Ramapithecus, Australopithecines and Homo habilis - who probably did not eat meat?Preview
  34. Q34Louis Pasteur’s experiments, if you recall, proved that life can arise from only pre-existing life. Can we correct this as life evolves from…Preview
  35. Q35The scientists believe that evolution is gradual. But extinction, part of evolutionary story, are 'sudden' and 'abrupt' and also group-speci…Preview
  36. Q36Why is nascent oxygen supported to be toxic to aerobic life forms?Preview
  37. Q37While creation and presence of variation is directionless, natural selection is directional as it is in the context of adaptation. Comment.Preview
  38. Q38The evolutionary story of moths in England during industrialisation reveals, that 'evolution is apparently reversible'. Clarify this stateme…Preview
  39. Q39Comment on the statement that "evolution and natural selection are end result or consequence of some other processes but themselves are not…Preview
  40. Q40State and explain any three factors affecting allele frequency in populations.Preview
  41. Q41Gene flow occurs through generations. Gene flow can occur across language barriers in humans. If we have a technique of measuring specific a…Preview
  42. Q42How do you express the meaning of words like race, breed, cultivars or variety?Preview
  43. Q43When we say "survival of the fittest", does it mean that a. those which are fit only survive, or b. those that survive are called fit? Comme…Preview
  44. Q44Enumerate three most characteristic criteria for designating a Mendelian population.Preview
  45. Q45"Migration may enhance or blurr the effects of selection". Comment.Preview
  46. Q46Name the law that states that the sum of allelic frequencies in a population remains constant. What are the five factors that influence thes…Preview
  47. Q47Explain divergent evolution in detail. What is the driving force behind it?Preview
  48. Q48You have studied the story of Pepper moths in England. Had the industries been removed, what impact could it have on the moth population? Di…Preview
  49. Q49What are the key concepts in the evolution theory of Darwin?Preview
  50. Q50Two organisms occupying a particular geographical area (say desert) show similar adaptive strategies. Taking examples, describe the phenomen…Preview
  51. Q51We are told that evolution is a continuing phenomenon for all living things. Are humans also evolving? Justify your answer.Preview
  52. Q52Had Darwin been aware of Mendel’s work, would he been able to explain the origin of variations. Discuss.Preview

CBSE Sample Papers

Questions from official CBSE sample papers.

+Show 11 questions11 questions
  1. Q1Observe the picture given below. Name the naturalist and write the explanation given by him that evolution of life forms had occurred on the…Preview
  2. Q2(a) Explain the significance of the experiment carried out by S.L. Miller. Name the scientists whose hypothesis prompted him to carry out th…Preview
  3. Q3A population is in genetic equilibrium/Hardy-Weinberg equilibrium for a gene with 2 alleles (dominant allele is 'A' and recessive allele 'a'…Preview
  4. Q4S.L. Miller in 1953, to support the theory of chemical evolution, created conditions in the closed flask that included : (A) CH3, O2, NH3, H…Preview
  5. Q5A population of snakes lived in a desert with brown sand. Study the drawings given below showing the change in the population from 'one' to…Preview
  6. Q6If a natural population with 50 individuals is in Hardy-Weinberg equilibrium for a gene with two alleles A and a, with the gene frequency of…Preview
  7. Q7The idea of use and disuse of organs for evolution of organism was proposed by (A) Charles Darwin (B) Thomas Malthus (C) Hugo De Vries (D) L…Preview
  8. Q8(a) How is Hardy-Weinberg expression (p2 + 2pq + q2) = 1 derived ? (b) List any two factors that disturb the genetic equilibrium.Preview
  9. Q9Write the names of the following : (a) A 15 mya primate that was ape-like (b) A 2 mya primate that lived in East African grasslandsPreview
  10. Q10With the help of an algebraic equation, how did Hardy-Weinberg explain that in a given population the frequency of occurrence of alleles of…Preview
  11. Q11(a) Differentiate between analogous and homologous structures. (b) Select and write analogous structures from the list given below : (i) Win…Preview