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Lamarck, Darwin and Peppered Moth ICSE Class 10

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BiologyICSE Class 10 · Human Evolution

Lamarck, Darwin, Vestigial Organs and the Peppered Moth: ICSE Class 10 Biology

Updated 18 October 2026 · Fact-checked

Lamarck said that organs used often become stronger and organs not used shrink, and that such acquired changes are inherited, but experiments show acquired characters are not inherited. Darwin said that over-production, struggle, variation and survival of the fittest lead to new species. The peppered moth shows natural selection: industrial melanism made dark moths common after trunks darkened.

Birds eat the moths they can see, so the colour matching the trunk survives: light before pollution, dark after soot, which is natural selection.

Illustration drawn for QuestionBuddy.

Understand Lamarck, Darwin, Vestigial Organs and the Peppered Moth

Lamarck's theory. Lamarck proposed two ideas. Use and disuse: organs that are used often become larger and stronger, and organs not used become smaller and may disappear. Inheritance of acquired characters: such changes gained during life are passed on to the offspring. For use, ancestral giraffes with short necks stretched to reach leaves high on trees, lengthening the neck and forelimbs a little; this was inherited, and over generations the neck became very long. For disuse, organs no longer used shrank over generations. Criticism: experiments show acquired characters are not inherited. When the tails of mice were cut off generation after generation, the young were still born with tails. Changes to body cells do not alter the genes in the gametes.

Vestigial organs. These are organs that are reduced and non-functional (or nearly so) in an organism but were well developed and functional in its ancestors, or are functional in related animals. In humans: wisdom teeth (third molars) in the mouth, which often do not erupt properly because jaws became smaller with a softer diet; the vermiform appendix, a small tube at the start of the large intestine, functional in plant-eating mammals for digesting cellulose; and the muscles of the pinna, since most humans cannot move their ears. They are evidence that humans evolved from ancestors in which these organs were useful.

Darwin's theory of natural selection.
1. Over-production: organisms produce far more offspring than can survive.
2. Struggle for existence: for food, space and mates, and against predators and disease.
3. Variation: no two individuals are exactly alike, and many variations are inherited.
4. Survival of the fittest: individuals with useful variations survive and reproduce more.
5. Inheritance: useful variations are passed on and accumulate.
6. Origin of species: over a very long time, accumulated variations give rise to new species.
For the giraffe, Darwin would say that giraffes varied in neck length; those with longer necks reached more food in times of shortage, survived and bred, passing on long necks.

Peppered moth (Biston betularia). It exists in a light (speckled) form and a dark (melanic) form. Before industrialisation, tree trunks were pale with lichens; light moths were camouflaged and common, while dark moths were easily eaten by birds. After industrialisation, soot killed the lichens and darkened the trunks; dark moths became camouflaged and common, and light ones were eaten. This change is industrial melanism. When pollution was later reduced and trunks lightened, the light form increased again. The environment, through birds as predators, selected the better camouflaged colour: survival of the fittest.

Lamarck, Darwin, Vestigial Organs and the Peppered Moth: key facts

Lamarck's chain
  • Use and disuse
  • acquired change
  • claimed to be inherited
  • not supported by experiments
Mouse tail experiment.
Darwin's chain
  • Over-production
  • struggle for existence
  • variation
  • survival of the fittest
  • inheritance
  • new species
Natural selection.
Human vestigial organs
  • Wisdom teeth
  • vermiform appendix
  • muscles of the pinna
Reduced in humans, functional in ancestors or related animals.

How to answer Lamarck, Darwin, Vestigial Organs and the Peppered Moth questions

Questions ask for a theory with an example, a comparison of Lamarck and Darwin, or the explanation of the peppered moth. Always give the example and a conclusion.

  1. 1Name the theory and its key idea in one line.
  2. 2Give the giraffe example in that theory's language.
  3. 3For Darwin, include variation, struggle and survival of the fittest.
  4. 4For the peppered moth, state background colour, which form is camouflaged and who selects (birds).
  5. 5Conclude with the change in frequency of the forms.

Lamarck, Darwin, Vestigial Organs and the Peppered Moth in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Natural selection of a colour form

Suppose a small beetle in a field has green and brown forms, and a drought turns the grass brown. Birds begin to eat many more green beetles (invented situation).

Using the peppered moth idea, explain what will happen to the proportion of the forms.

Try it first, then show the solutionSolution
  1. Brown beetles are camouflaged on brown grass.
  2. Green beetles are seen and eaten.
  3. Survivors breed, so the brown form increases.

Answer: Brown beetles are camouflaged against the dry grass, so birds eat more green beetles. The brown beetles survive and breed more, passing on their colour, so the brown form becomes common, just as the dark peppered moth did on soot-darkened trunks.

Memory hook: The environment selects the better camouflaged.

Acquired characters are not inherited

Suppose a weightlifter builds large muscles through years of training and later has a child.

Would Lamarck expect the child to be born muscular, and what does the evidence say?

Try it first, then show the solutionSolution
  1. Lamarck: acquired characters are inherited.
  2. Experiments such as the cut tails of mice show they are not.

Answer: Lamarck would expect the child to inherit the strength, but experiments, such as the mice whose tails were cut for generations and whose young still had tails, show acquired characters are not inherited. Changes to body cells do not alter the genes in the gametes.

Memory hook: Training changes you, not your genes.

Tricks to remember Lamarck, Darwin, Vestigial Organs and the Peppered Moth

Short memory aids. Say each one aloud once, then use it on a question the same day.

  • O-S-V-S-I-O

    Over-production, Struggle, Variation, Survival, Inheritance, Origin of species.

    Use it when: Steps of Darwin's theory.

  • W-A-P

    Wisdom teeth, Appendix, Pinna muscles.

    Use it when: Vestigial organs in humans.

  • Soot makes dark moths safe

    Dark trunks, dark moths common: industrial melanism.

    Use it when: Peppered moth.

Lamarck, Darwin, Vestigial Organs and the Peppered Moth: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Vestigial organ · 1 mark · MCQBoard level

Which of these is a vestigial organ in humans?
(a) heart
(b) vermiform appendix
(c) liver
(d) kidney

Try it first, then show the solutionSolution
  1. The vermiform appendix is reduced; it was functional in plant-eating mammals (1 mark).

Answer: (b) vermiform appendix

Example 2: Lamarck's two ideas (2 marks) · 2 marks · Very short answerBoard level

State the two ideas of Lamarck's theory and give one criticism. (2 marks)

Try it first, then show the solutionSolution
  1. Use and disuse of organs; inheritance of acquired characters (1 mark).
  2. Criticism: experiments, such as cutting mice tails generation after generation, show acquired characters are not inherited (1 mark).

Answer: Lamarck proposed use and disuse of organs and the inheritance of acquired characters. It is criticised because experiments show acquired characters are not inherited: mice whose tails were cut for generations were still born with tails.

Example 3: Giraffe: Lamarck versus Darwin (4 marks) · 4 marks · Short answerHarder board level

A student writes: 'Giraffes grew long necks because they kept stretching them and their calves were born with longer necks.' Identify whose theory this is, give one piece of evidence against it, and restate the explanation in Darwin's terms. (4 marks)

Try it first, then show the solutionSolution
  1. It is Lamarck's theory of use and inheritance of acquired characters (1 mark).
  2. Evidence against: mice whose tails were cut for generations were still born with tails (1 mark).
  3. Darwin: giraffes varied in neck length; longer-necked ones got more food in shortage (1 mark).
  4. They survived, bred and passed on long necks, so long necks became common (1 mark).

Answer: It is Lamarck's theory. Evidence against it is that acquired characters are not inherited: mice whose tails were cut off for generations were still born with tails. In Darwin's terms, giraffes varied naturally in neck length; those with longer necks reached more food in shortage, survived and bred, passing on long necks until they became common.

Example 4: Peppered moth (5 marks) · 5 marks · Long answerHarder board level

Two woods are studied: Wood A has pale lichen-covered trunks and Wood B has trunks blackened by soot. Predict which form of peppered moth will be commoner in each, and justify using the ideas of camouflage, predation and natural selection. (5 marks)

Try it first, then show the solutionSolution
  1. Two forms: light (speckled) and dark (melanic) (1 mark).
  2. Before industrialisation, pale lichen-covered trunks: light moths camouflaged and common (1 mark).
  3. After industrialisation, soot darkened trunks: dark moths camouflaged, light ones eaten by birds (1 mark).
  4. Dark form became common: industrial melanism (1 mark).
  5. With reduced pollution the light form increased again; environment selected the fitter form (1 mark).

Answer: The peppered moth has a light form and a dark form. In Wood A, with pale lichen-covered trunks, light moths are camouflaged and common while birds eat the dark moths. In Wood B, where soot has killed lichens and darkened the trunks, dark moths are camouflaged and light ones are eaten, so the dark form becomes common; this is industrial melanism. If pollution fell and trunks lightened, the light form would increase again. The environment, through bird predation, selects the better camouflaged form: survival of the fittest.

Example 5: Evidence from vestigial organs · 4 marks · Case-basedHOTS / competency

Wisdom teeth often do not erupt properly in modern humans. (i) Name the type of organ. (1) (ii) Give a reason for their reduction. (1) (iii) How do such organs support evolution? (2)

Try it first, then show the solutionSolution
  1. (i) Vestigial organ (1 mark).
  2. (ii) Human jaws became smaller with a softer diet (1 mark).
  3. (iii) They were well developed in ancestors, so humans evolved from ancestors in which these organs were useful (2 marks).

Answer: (i) A vestigial organ. (ii) Human jaws became smaller with a softer diet. (iii) Such organs were well developed and functional in ancestors, which is evidence that humans evolved from those ancestors.

Where students lose marks in Lamarck, Darwin, Vestigial Organs and the Peppered Moth

The slips examiners see most often, and what to write instead.

  • Mistake: Writing that giraffes stretched necks in Darwin's theory

    Mixing the two explanations.

    Wrong working

    Darwin: giraffes stretched their necks and the change was inherited.

    Right working

    Darwin: natural variation in neck length; longer-necked giraffes survived and bred.

    Do this: Lamarck stretches; Darwin selects.

    Usually costs: 2 marks.

  • Mistake: Not naming who selects in the peppered moth

    Skipping predators.

    Wrong working

    Dark moths changed colour because of pollution.

    Right working

    Birds ate the less camouflaged moths, so the better camouflaged form survived and became common.

    Do this: Name the predator and camouflage.

    Usually costs: 1 mark.

  • Mistake: Calling vestigial organs useless

    Oversimplifying.

    Wrong working

    Vestigial organs have no use at all.

    Right working

    They are reduced and non-functional (or nearly so) but were functional in ancestors or related animals.

    Do this: Use the definition.

    Usually costs: 1 mark.

Exam tips

  • For the giraffe, write both theories in parallel lines.
  • Include the criticism of Lamarck with the mouse tail experiment.
  • For percentages, show remaining numbers before dividing.

Practice questions on Lamarck, Darwin, Vestigial Organs and the Peppered Moth

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

  1. Q1 · 1 mark · MCQBoard level

    Industrial melanism refers to:
    (a) the death of moths in factories
    (b) the increase of dark forms where soot darkened the surroundings
    (c) the colour of lichens
    (d) the migration of moths

    Hint

    Peppered moth after industrialisation.

    Answer

    (b) the increase of dark forms where soot darkened the surroundings

  2. Q2 · 2 marks · Very short answerBoard level

    Name any two vestigial organs of humans. (2 marks)

    Hint

    Teeth, intestine, ear.

    Answer

    Any two of wisdom teeth, vermiform appendix and the muscles of the pinna.

  3. Q3 · 3 marks · Short answerHarder board level

    A population of 200 moths has 20 dark and 180 light moths on pale trunks. After soot darkens the trunks, birds eat 150 of the light moths and 4 of the dark moths. Find the numbers left, the percentage of dark moths after selection, and name the process. (3 marks)

    Hint

    Remaining dark = 20 - 4; remaining light = 180 - 150.

    Answer

    Dark left = 20 - 4 = 16; light left = 180 - 150 = 30; total = 46. Percentage dark = 16 / 46 x 100 = 34.8 per cent (about 35), compared with 10 per cent earlier. The process is natural selection (industrial melanism).

  4. Q4 · 5 marks · Long answerHarder board level

    Compare Lamarck's and Darwin's theories on the cause of variation, the fate of acquired changes and the example of the giraffe, and give one reason why Darwin's theory is accepted. (5 marks)

    Hint

    Use and disuse versus natural selection.

    Answer

    Lamarck said change comes from use and disuse of organs, and acquired changes are inherited; giraffes lengthened their necks by stretching. Darwin said variations occur naturally and are inherited; those with useful variations survive and breed more; giraffes with longer necks survived in food shortage. Experiments show that acquired characters, like the cut tails of mice, are not inherited, so Lamarck's idea is not supported, while Darwin's natural selection is supported by observations such as the peppered moth.

  5. Q5 · 1 mark · Assertion-reasonHOTS / competency

    Assertion (A): Darwin's theory explains why the dark form of the peppered moth became common after industrialisation.
    Reason (R): Birds ate the better camouflaged moths more.
    (a) Both A and R are true, and R is the correct explanation of A.
    (b) Both A and R are true, but R is not the correct explanation of A.
    (c) A is true, but R is false.
    (d) A is false, but R is true.

    Hint

    Who is camouflaged?

    Answer

    (c) A is true, but R is false. Birds ate the less camouflaged moths.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

  1. 1.What is industrial melanism?Show answer

    The increase of dark forms in polluted areas where soot darkened the surroundings.

  2. 2.What is the scientific name of the peppered moth?Show answer

    Biston betularia.

  3. 3.Who proposed natural selection?Show answer

    Darwin.

  4. 4.What are the vestigial organs of humans in the syllabus?Show answer

    Wisdom teeth, vermiform appendix and pinna muscles.

Lamarck, Darwin, Vestigial Organs and the Peppered Moth: frequently asked questions

What is the difference between Lamarck's and Darwin's theories?

Lamarck: use and disuse with inheritance of acquired characters; Darwin: natural selection of inherited variations.

What is survival of the fittest?

The survival and greater reproduction of individuals with useful variations.

Why are vestigial organs evidence of evolution?

They were well developed in ancestors, showing descent from them.