Class 12 Biology Chapter 6 Evolution Solutions. Explore Class 12 Biology Chapter 6 Evolution Solutions with easy-to-understand answers, important questions, and exam-focused explanations to strengthen your concepts, revise effectively, and prepare confidently for exams.

Class 12 Biology Chapter 6 Evolution Solutions

A. Very Short Answer Questions (1 mark each)

1. Who proposed theories of biological evolution?

Ans: Several scientists contributed to evolutionary theory, including Lamarck, Weismann, Darwin and de Vries.

2. Why was it believed that life originated in seawater?

Ans: Seawater contains many inorganic substances that could have participated in the chemical processes involved in the origin of life.

3. What is a protovirus?

Ans: The source defines a protovirus as an early stage of a virus; this is not a standard, widely used term in modern biology.

4. What are homologous and analogous organs?

Ans: Homologous organs have the same basic origin and structural plan but may perform different functions. Analogous organs have different origins and structures but perform similar functions.

5. Which fossil serves as a connecting link between birds and reptiles?

Ans: Archaeopteryx.

6. What is palaeontology?

Ans: Palaeontology is the branch of science that studies fossils.

7. Why is the platypus called a living fossil?

Ans: The platypus retains a combination of primitive and specialised features often used to illustrate evolutionary relationships between reptiles and mammals. “Living fossil” is an informal term.

8. In which book did Lamarck present his explanation of evolution?

Ans: Philosophie Zoologique (Zoological Philosophy), published in 1809.

9. According to de Vries, what is the main cause of evolution?

Ans: Mutations.

10. What is the mutation theory?

Ans: The mutation theory proposes that evolution can occur through sudden, heritable changes (mutations), which may contribute to the origin of new species. Evolution is not necessarily always progressive.

11. What is discontinuous distribution?

Ans: It is a pattern in which related organisms occur in geographically separated regions, with no continuous distribution between them.

12. What is the main basis of Weismann’s theory of evolution?

Ans: Weismann argued that hereditary information is transmitted through germ cells; changes acquired by the body during an organism’s lifetime are generally not inherited.

13. From which archipelago did Darwin obtain important evidence for his studies?

Ans: The Galápagos Islands.

14. When can a founder population contribute to the formation of a new species?

Ans: When a small group establishes a new population, allele frequencies may change through the founder effect and genetic drift. If reproductive isolation develops, a new species may eventually arise.

15. What conclusion can be drawn from comparing the blood serum of humans and other animals?

Ans: Serological comparisons indicate evolutionary relationships: humans are more closely related to chimpanzees than to baboons or dogs.

16. How can the age of a living tree be determined?

Ans: By counting its annual growth rings in a cross-section of the trunk. Radiocarbon dating is not the usual method for determining the age of a living tree.

17. What is the main idea of the Hardy–Weinberg principle? H S ‘24

Ans: In a large, randomly mating population, allele and genotype frequencies remain constant if mutation, migration, natural selection and genetic drift are absent. This is genetic equilibrium.

Fill in the Blanks (Class 12 Biology Chapter 6 Evolution Solutions)

18. Amino acids join together to form a ______ molecule.

Ans: Protein.

19. Darwin’s theory had two main components: ______ and ______.

Ans: The struggle for existence and natural selection (often summarised as “survival of the fittest” and natural selection).

20. The doctrine of ______ explains the theory of special creation.

Ans: The source’s intended word appears to be “religion” or “theological”; the wording is unclear in the supplied text.

21. ______ indicates a common ancestry.

Ans: Homology (homologous structures).

22. ______ serve as a connecting link in the evolution of present-day plants and animals.

Ans: The source gives “finches”; this is not a generally accepted connecting-link example, and the intended answer is unclear.

23. Genetic drift changes the gene frequencies of a ______.

Ans: Population.

24. Darwin was influenced by ______’s work on populations.

Ans: Thomas Robert Malthus.

B. Short-Answer Questions (2 marks each)

25. What is the modern theory of the origin of life?

Ans: The chemical-evolution hypothesis proposes that, on the early Earth, simple inorganic substances formed increasingly complex organic molecules through chemical reactions. These molecules may have assembled into aggregates such as coacervates, from which more organised, cell-like systems eventually arose. The process is commonly described as chemical evolution followed by biological evolution.

26. Describe Miller’s experiment on the chemical origin of life.

Ans: Miller circulated water vapour with methane (CH₄), ammonia (NH₃) and hydrogen (H₂) through an apparatus exposed to electrical sparks. A condenser cooled the gases, allowing the mixture to circulate. After about a week, the liquid became coloured. Analysis found organic compounds, including amino acids such as glycine and alanine. The experiment showed that some organic molecules could form under simulated early-Earth conditions.

27. Which theory of the origin of life is widely accepted, and who proposed it?

Ans: The chemical-evolution hypothesis is widely taught as an explanation for the origin of life. It was proposed independently by Alexander Oparin and J. B. S. Haldane.

28. How is the age of fossils determined?

Ans: Fossil age may be estimated from the surrounding rock layers (relative dating) or by radiometric dating. Carbon-14 dating is useful for relatively recent organic remains, generally up to about 50,000 years. Older rocks may be dated using uranium–lead; U-238 has a half-life of about 4.5 billion years. The source’s 450-crore-year figure approximates one half-life, not complete conversion.

29. What conclusions can be drawn from the study of fossils?

Ans: (i) Organisms have changed in form over geological time. (ii) Older strata often contain organisms with simpler structures, though evolution is not a universal linear progression. (iii) Transitional fossils can indicate evolutionary relationships. (iv) Fossils help establish the sequence and approximate timing of the appearance and extinction of organisms.

30. How do Darwin’s finches illustrate adaptive radiation?

Ans: Darwin’s finches descended from a common ancestral population that reached the Galápagos Islands. Different populations adapted to different ecological niches, especially food sources, and natural selection favoured different beak forms. Over time, populations diverged into distinct species. This diversification from a common ancestor is adaptive radiation.

31. What were the limitations of Lamarck’s theory?

Ans: Lamarck emphasised environmental influence and adaptation, but his claim that acquired characteristics are inherited was not supported as a general mechanism. Changes caused by use or disuse are not ordinarily transmitted to offspring through hereditary material.

32. What were the limitations of Darwin’s theory?

Ans: (i) Darwin could not explain the genetic mechanism by which variations arise. (ii) He did not know the mechanisms of genes, mutation or inheritance. (iii) Natural selection explains differential survival and reproduction of heritable variants, but variation itself requires genetic explanations.

33. Explain the Lamarckian, Darwinian and modern theories of evolution.

Ans: (a) Lamarckian theory: The environment creates new needs; use and disuse produce changes, and acquired characteristics are inherited. This claim is not accepted as a general explanation today. (b) Darwinian theory: Organisms produce more offspring than can survive; individuals vary; competition occurs; and individuals with advantageous heritable variations tend to survive and reproduce more. (c) Modern synthetic theory: Evolution results from changes in allele frequencies caused by mutation, recombination, gene flow, genetic drift and natural selection; reproductive isolation contributes to speciation.

34. What are convergent and divergent evolution? Explain with examples.

Ans: Convergent evolution occurs when unrelated groups independently evolve similar adaptations, such as the wings of birds and insects. Divergent evolution occurs when related organisms from a common ancestor become different as they adapt to different conditions. The human arm, bat wing and whale flipper are homologous forelimbs illustrating divergent evolution.

C. Descriptive Questions (3–5 marks each)

35. What is speciation? Describe the process.

Ans: Speciation is the formation of new species. Variation arises through mutation and recombination. Natural selection, genetic drift and restricted gene flow can cause populations to diverge. When populations become reproductively isolated by geographical, behavioural, ecological or other barriers, they may stop exchanging genes. Accumulated differences can eventually result in distinct species.

36. What geographical evidence supports evolution?

Ans: (i) Organisms in different regions often show relationships reflecting ancestry and geographical history. (ii) Migration and dispersal explain how organisms reach new areas. (iii) Isolated populations may adapt to different environments and diverge. (iv) Island species often resemble nearby mainland species but show distinctive adaptations. (v) Geographic barriers can restrict gene flow and contribute to speciation.

37. Is mutation important in evolution? Explain.

Ans: Yes. Mutations create new genetic variants and are a primary source of new alleles. Most are neutral or harmful, while some may be beneficial in a particular environment. Heritable mutations can spread or disappear through natural selection, genetic drift and gene flow. De Vries emphasised sudden mutations, but modern evolutionary biology does not explain evolution by rare, sudden mutations alone. Artificially induced mutations can be used in plant breeding, but their outcomes are unpredictable and require selection.

38. Discuss the arguments of Lamarck’s theory.

Ans: (a) Environmental influence: Lamarck argued that environmental changes create new needs and habits. (b) Development according to need: organs were proposed to develop or change in response to needs. (c) Use and disuse: frequently used organs were thought to strengthen, while unused organs weakened or disappeared. (d) Inheritance of acquired characteristics: Lamarck proposed that changes acquired during life are passed to offspring. Modern genetics does not support this as a general mechanism of evolution.

39. Discuss the main foundations of Darwin’s theory of natural selection.

Ans: (a) Overproduction: Organisms produce more offspring than can survive. (b) Struggle for existence: Limited resources create competition and environmental challenges. (c) Variation: Individuals differ, and some differences are heritable. (d) Natural selection: Individuals with advantageous heritable traits tend to survive and reproduce more successfully. (e) Differential reproductive success: Favourable traits become more common over generations. (f) Speciation: Divergence and reproductive isolation may eventually lead to new species.

40. Discuss the modern synthetic theory of evolution. H S ‘24

Ans: The modern synthetic theory combines Darwin’s natural selection with genetics. Evolution is a change in allele frequencies in populations over generations. Its main mechanisms are mutation, genetic recombination, gene flow, genetic drift and natural selection. Mutation and recombination generate variation; gene flow moves alleles between populations; genetic drift changes frequencies by chance; natural selection favours heritable traits that improve reproductive success. Reproductive isolation can allow populations to diverge and form new species.

41. Discuss the modern concept of genes and genetic equilibrium.

Ans: The Hardy–Weinberg principle states that allele and genotype frequencies remain constant in an ideal population with random mating, a very large population, and no mutation, migration, natural selection or genetic drift. In real populations, these forces may change allele frequencies. Mutation introduces new alleles; gene flow transfers alleles; genetic drift causes random changes; recombination reshuffles existing alleles; and natural selection changes frequencies according to reproductive success. Recombination usually creates new combinations rather than new alleles.

42. Discuss the origin and evolution of humans.

Ans: Human evolution occurred over millions of years and involved several hominin species, not a simple linear sequence. Early hominins evolved in Africa. Australopithecines walked upright; later members of Homo showed changes in brain size, tool use and behaviour. Homo habilis is associated with early stone-tool use; Homo erectus spread beyond Africa; Neanderthals lived in Europe and parts of western Asia; and Homo sapiens arose in Africa roughly 300,000 years ago and later spread worldwide. Modern humans share common ancestors with other living apes; humans did not evolve from chimpanzees alive today.

D. Additional Questions and Answers (Class 12 Biology Chapter 6 Evolution Solutions)

1. What is the main feature of Darwin’s theory?

Ans: Natural selection acts on heritable variation: individuals better adapted to their environment tend to leave more offspring, so advantageous traits become more common over generations.

2. What causes evolution through mutation or variation?

Ans: Mutation introduces new genetic variants, while recombination creates new combinations of existing alleles. Natural selection, genetic drift and gene flow affect how these variants change in frequency. De Vries proposed that sudden mutations could contribute to new species, but modern theory does not treat mutation as the sole cause of evolution.

3. What happens to populations when herbicides or pesticides are used?

Ans: Repeated use can select for resistant individuals. Those that survive reproduce, causing resistance alleles to become more common in the population.

4. How did the first mammals arise?

Ans: Mammals evolved from synapsid ancestors. The earliest mammals appeared during the Mesozoic Era and were generally small. Mammalian characteristics, including hair and milk production, evolved over time. Mammals later diversified into many ecological roles, especially after the end-Cretaceous extinction.

5. What is the role of sexual reproduction in evolution by natural selection?

Ans: Sexual reproduction recombines genetic material from two parents, creating new combinations of alleles. This variation provides material on which natural selection can act.

6. What promotes the formation of new species?

Ans: The accumulation of genetic differences, reduced gene flow and reproductive isolation promote speciation. Mutation, recombination, natural selection and genetic drift contribute to divergence.

7. What are the characteristics of the theory of special creation?

Ans: According to the doctrine of special creation, living organisms were created in their present forms by a supernatural creator and were considered essentially unchanging. This is a historical belief, not a scientific theory supported by modern evolutionary evidence. The source’s claim that Earth is about 4,000 years old is inconsistent with scientific evidence; Earth is about 4.54 billion years old.

8. What are some human influences on the evolution of plants and animals?

Ans: Humans have domesticated plants and animals and selectively bred them for desired traits, including food production and other uses. Artificial selection can produce varieties that differ substantially from their wild ancestors.

9. Can human evolution be described as adaptive radiation?

Ans: Human evolution is not usually described as adaptive radiation in the same way as Darwin’s finches. The human lineage is one branch of the primate evolutionary tree, which diversified from common ancestors into multiple lineages. Adaptive radiation is more appropriate for diversification into several species adapted to different ecological niches.

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