Class 12 Biology – Evolution Notes

Class 12 Biology – Evolution Notes

Evolution – Short Notes

1. Meaning of Evolution

  • Evolution: Gradual change in heritable traits of populations over generations.
  • Explains origin of species and biodiversity.

2. Theories of Evolution

  1. Lamarckism (Jean-Baptiste Lamarck)
    • Theory of Use and Disuse: Organs develop or shrink based on usage.
    • Inheritance of acquired characters: Traits acquired during life are passed to offspring.
    • Example: Giraffe’s long neck.
  2. Darwinism (Charles Darwin)
    • Natural Selection: Individuals with favorable traits survive and reproduce.
    • Survival of the fittest.
    • Steps: Variation → Struggle for existence → Selection → Evolution.
  3. Neo-Darwinism / Synthetic Theory
    • Combines Mendelian genetics and Darwin’s theory.
    • Population genetics explains evolution as changes in allele frequencies.

3. Evidences of Evolution

  1. Fossil Record: Shows gradual changes over time.
  2. Comparative Anatomy:
    • Homologous structures → common ancestry (e.g., forelimbs of vertebrates).
    • Analogous structures → convergent evolution (e.g., wings of birds & insects).
  3. Comparative Embryology: Similar embryonic development in related species.
  4. Molecular Biology: Similarities in DNA, RNA, and proteins indicate evolutionary relationships.
  5. Biogeography: Distribution of species reflects evolutionary history.

4. Mechanisms of Evolution

  • Mutation – Source of genetic variation.
  • Genetic Drift – Random changes in allele frequencies in small populations.
  • Gene Flow / Migration – Movement of alleles between populations.
  • Natural Selection – Favorable traits increase survival and reproduction.
  • Speciation – Formation of new species due to genetic changes and reproductive isolation.

5. Types of Evolution

  1. Divergent Evolution – One species evolves into several species (e.g., Darwin’s finches).
  2. Convergent Evolution – Unrelated species develop similar traits (e.g., wings of bats & birds).
  3. Parallel Evolution – Related species evolve similarly after separation.
  4. Co-evolution – Two species evolve in response to each other (e.g., flower & pollinator).

Evolution | MCQs

1. Theories of Evolution

  1. The theory of inheritance of acquired characters was proposed by:
    a) Darwin
    b) Mendel
    c) Lamarck
    d) Hugo de Vries
    Answer: c) Lamarck
  2. Darwin’s theory of natural selection is based on:
    a) Use and disuse
    b) Mutation only
    c) Survival of the fittest
    d) Artificial selection
    Answer: c) Survival of the fittest
  3. According to Darwin, evolution occurs due to:
    a) Sudden mutations
    b) Natural selection acting on variations
    c) Inheritance of acquired traits
    d) Genetic drift only
    Answer: b) Natural selection acting on variations
  4. Neo-Darwinism combines Darwin’s theory with:
    a) Cell theory
    b) Chromosomal theory
    c) Mendelian genetics
    d) Germ theory
    Answer: c) Mendelian genetics

2. Evidences of Evolution

  1. Fossils are:
    a) Living organisms
    b) Preserved remains of organisms
    c) Embryos
    d) Mutations
    Answer: b) Preserved remains of organisms
  2. Homologous organs indicate:
    a) Convergent evolution
    b) Common ancestry
    c) Mutation
    d) Artificial selection
    Answer: b) Common ancestry
  3. Wings of birds and insects are examples of:
    a) Homologous organs
    b) Analogous organs
    c) Vestigial organs
    d) Mutations
    Answer: b) Analogous organs
  4. Similar embryonic stages in vertebrates suggest:
    a) Artificial selection
    b) Common origin
    c) Mutation
    d) Isolation
    Answer: b) Common origin
  5. Molecular evidence of evolution is based on comparison of:
    a) Fossils
    b) Bones
    c) DNA and protein sequences
    d) Organs
    Answer: c) DNA and protein sequences

3. Mechanisms of Evolution

  1. Sudden heritable change in DNA is called:
    a) Selection
    b) Mutation
    c) Speciation
    d) Migration
    Answer: b) Mutation
  2. Genetic drift is more significant in:
    a) Large populations
    b) Small populations
    c) All populations equally
    d) Plants only
    Answer: b) Small populations
  3. Movement of individuals from one population to another is called:
    a) Mutation
    b) Natural selection
    c) Gene flow
    d) Speciation
    Answer: c) Gene flow
  4. Natural selection results in:
    a) Decrease in favorable traits
    b) Increase in harmful traits
    c) Increase in favorable traits
    d) No change
    Answer: c) Increase in favorable traits
  5. Formation of new species is known as:
    a) Mutation
    b) Speciation
    c) Variation
    d) Reproduction
    Answer: b) Speciation

4. Hardy-Weinberg Principle

  1. Hardy-Weinberg principle explains:
    a) Mutation rate
    b) Genetic equilibrium in population
    c) Speciation
    d) Natural selection only
    Answer: b) Genetic equilibrium in population
  2. According to Hardy-Weinberg equilibrium:
    a) Allele frequencies remain constant in absence of evolutionary forces
    b) Mutations stop evolution
    c) Evolution stops permanently
    d) Selection does not occur
    Answer: a) Allele frequencies remain constant in absence of evolutionary forces
  3. Which of the following disturbs Hardy-Weinberg equilibrium?
    a) No mutation
    b) No migration
    c) Natural selection
    d) Random mating
    Answer: c) Natural selection

5. Types of Evolution

Co-evolution occurs when:
a) One species evolves
b) Two species evolve together
c) Mutation occurs
d) Fossils form
Answer: b) Two species evolve together

Evolution of different species from a common ancestor is called:
a) Convergent evolution
b) Divergent evolution
c) Parallel evolution
d) Artificial selection
Answer: b) Divergent evolution

Development of similar traits in unrelated species is called:
a) Divergent evolution
b) Parallel evolution
c) Convergent evolution
d) Mutation
Answer: c) Convergent evolution