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Evolution – Class 12 Biology notes, important questions and MCQs

NCERT Class 12 Biology, chapter 6. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Life evolved from simple chemicals over billions of years. Evidence from fossils, anatomy and molecules supports evolution by natural selection, and human evolution can be traced through hominid fossils.

Origin and evidence

Miller–Urey experiment produced amino acids from simple gases with electric sparks.
Homologous organs (same origin, different function, e.g. forelimbs) show divergent evolution; analogous organs (different origin, same function, e.g. wings of bird and insect) show convergent evolution.
Industrial melanism in peppered moths shows natural selection in action.

Mechanisms and humans

Darwin: natural selection of the fittest; de Vries: mutations (saltation).
Hardy–Weinberg equilibrium (p² + 2pq + q² = 1) is disturbed by gene flow, drift, mutation, recombination and selection.
Human line: Dryopithecus → Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Neanderthals → Homo sapiens.

Key terms

Adaptive radiation: evolution of many forms from one ancestor into different habitats, e.g. Darwin's finches
Genetic drift: change in allele frequency by chance, strong in small populations
Convergent evolution: unrelated organisms evolving similar features because they live in similar habitats, e.g. wings of birds and insects

Formulas

p² + 2pq + q² = 1

Important questions with answers

What is the evidence from industrial melanism in peppered moths?2 marks

Before industrialisation, light-coloured moths were common on pale lichen-covered trees. After soot darkened tree trunks, dark moths were better hidden from birds and became more common. This showed natural selection acting in a short time.

Name the five factors that disturb Hardy–Weinberg equilibrium.3 marks

Gene migration (gene flow), genetic drift, mutation, genetic recombination during gametogenesis, and natural selection.

Explain Darwin's theory of natural selection and compare it with de Vries' mutation theory.5 marks

Darwin: organisms produce more offspring than can survive, so there is a struggle for existence; individuals show variations, some of which are heritable; those with useful variations survive and reproduce more (survival of the fittest); over many generations these variations accumulate and new species arise gradually. De Vries, working on evening primrose, proposed that large sudden changes (mutations, saltation) cause speciation in a single step. Darwin's variations are small and directional; de Vries' mutations are large, random and sudden.

Quick revision

Darwin's finches show adaptive radiation.
Hardy–Weinberg: p + q = 1.
Homo habilis was the first to make tools.

Exam tips

Homologous → divergent; analogous → convergent.
Distinguish clearly: homologous organs → divergent evolution; analogous organs → convergent evolution.

Practice MCQs

Wings of a bird and an insect are
1. homologous
2. analogous
3. vestigial
4. identical
Show answer
Answer: (b) analogous. Same function, different origin.
Natural selection was proposed by
1. Lamarck
2. de Vries
3. Mendel
4. Darwin
Show answer
Answer: (d) Darwin. Darwin.
Miller's experiment produced
1. amino acids
2. DNA
3. cells
4. proteins only
Show answer
Answer: (a) amino acids. From CH₄, NH₃, H₂, H₂O.
Darwin's finches are an example of
1. convergent evolution
2. genetic drift only
3. industrial melanism
4. adaptive radiation
Show answer
Answer: (d) adaptive radiation. Adaptive radiation.
The theory of use and disuse of organs was proposed by
1. Darwin
2. Lamarck
3. de Vries
4. Wallace
Show answer
Answer: (b) Lamarck. Inheritance of acquired characters.
If q² = 0.16 in a Hardy–Weinberg population, frequency of heterozygotes (2pq) is
1. 0.48
2. 0.24
3. 0.36
4. 0.16
Show answer
Answer: (a) 0.48. q = 0.4, p = 0.6, 2pq = 0.48.
The first hominid known to make stone tools was
1. Australopithecus
2. Homo erectus
3. Homo habilis
4. Neanderthal
Show answer
Answer: (c) Homo habilis. "Handy man".
Australian marsupials evolving into many forms from a common ancestor is an example of
1. convergent evolution
2. industrial melanism
3. genetic drift
4. adaptive radiation
Show answer
Answer: (d) adaptive radiation. Radiation into many habitats.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.