Evidence for Evolution – Important Definitions class 12 cbse

Evidence for Evolution – Important Definitions

1. Evolution

  • Definition: Evolution is the gradual change in inherited characteristics of organisms over generations, leading to the formation of new species.

2. Fossils

  • Definition: Fossils are the preserved remains, impressions, or traces of ancient organisms found in sedimentary rocks.

3. Paleontology

  • Definition: The branch of biology that studies fossils.

4. Paleontological Evidence

  • Definition: Evidence for evolution obtained from the study of fossils.

5. Embryology

  • Definition: The study of the development of embryos.

6. Comparative Anatomy

  • Definition: The study of similarities and differences in the anatomical structures of different organisms.

7. Homologous Organs

  • Definition: Organs having the same basic structure and common origin but performing different functions.

Examples

  • Forelimbs of human, whale, bat and cheetah.
  • Thorn of Bougainvillea and tendril of Cucurbita.

8. Divergent Evolution

  • Definition: Evolution in which organisms with a common ancestor evolve into different forms due to adaptation to different environments.

9. Analogous Organs

  • Definition: Organs having different origin and structure but performing similar functions.

Examples

  • Wings of birds and butterflies.
  • Eye of octopus and mammals.
  • Flippers of penguins and dolphins.
  • Potato (stem) and sweet potato (root).

10. Convergent Evolution

  • Definition: Evolution in which unrelated organisms independently develop similar adaptations due to similar environmental conditions.

11. Biochemical Evidence

  • Definition: Similarities in DNA, genes and proteins among organisms that indicate common ancestry.

12. Artificial Selection

  • Definition: Selection carried out by humans to produce desirable varieties or breeds.

13. Natural Selection

  • Definition: Process in which organisms with favourable traits survive and reproduce more successfully.

14. Industrial Melanism

  • Definition: Increase in the frequency of dark-coloured individuals in polluted industrial areas due to natural selection.

15. Anthropogenic Evolution

  • Definition: Evolution caused by human activities such as excessive use of antibiotics, pesticides and herbicides.

Important Facts for CBSE Board Exam

Fossil Evidence

  • Fossils are found mainly in sedimentary rocks.
  • Older fossils occur in deeper rock layers.
  • Fossils help determine the geological age of organisms.
  • Fossils provide direct evidence for evolution.
  • Dinosaurs are examples of extinct organisms.

Embryological Evidence

  • Proposed by Ernst Haeckel.
  • Human embryo shows temporary gill slits.
  • Gill slits are functional only in fishes.
  • Karl Ernst von Baer disproved Haeckel’s idea that embryos pass through adult stages of lower animals.
  • Embryos resemble one another only during early stages.

Homologous Organs

  • Same origin.
  • Similar internal structure.
  • Different functions.
  • Evidence of common ancestry.
  • Indicate divergent evolution.

Analogous Organs

  • Different origin.
  • Different internal structure.
  • Same function.
  • Result of convergent evolution.
  • Do not indicate common ancestry.

Divergent Evolution

  • Common ancestor.
  • Different adaptive radiation.
  • Produces homologous organs.

Convergent Evolution

  • Different ancestors.
  • Similar adaptations.
  • Produces analogous organs.

Biochemical Evidence

  • Similar DNA sequences.
  • Similar proteins.
  • Similar genes.
  • Indicates common ancestry.

Artificial Selection

Examples:

  • Dog breeds.
  • Crop varieties.
  • Domestic animals.

Shows that selection can produce new varieties within a short time.

Industrial Melanism (Peppered Moth Example)

  • Before industrialization:
    • White moths were more common.
    • Trees covered with white lichens.
  • After industrialization:
    • Tree trunks became black due to soot.
    • Dark moths survived better.
    • White moths were easily eaten by predators.
  • Demonstrates natural selection.

Lichens

  • Excellent indicators of air pollution.
  • Do not grow in polluted areas.

Antibiotic Resistance

  • Excessive antibiotic use selects resistant bacteria.
  • Resistant bacteria survive and multiply.
  • Example of evolution occurring over months or years.

Herbicide and Pesticide Resistance

  • Excessive use selects resistant weeds and insects.
  • Demonstrates evolution by natural selection.

Important One-Line Facts

  • Fossils are direct evidence of evolution.
  • Homology → Divergent evolution.
  • Analogy → Convergent evolution.
  • Homologous organs indicate common ancestry.
  • Analogous organs indicate similar adaptation, not common ancestry.
  • Similar proteins and genes support evolution.
  • Artificial selection is performed by humans.
  • Industrial melanism is the best example of natural selection.
  • Lichens are indicators of air pollution.
  • Evolution is a stochastic (chance-based) process, not a directed one.
  • Mutation provides the raw material for evolution.
  • Natural selection acts on existing variations.

CBSE Most Important Examples (Remember)

ConceptExample
FossilDinosaur
Homologous organsHuman arm, whale flipper, bat wing, cheetah forelimb
Plant homologyThorn of Bougainvillea – Tendril of Cucurbita
Analogous organsBird wing – Butterfly wing
AnalogyEye of octopus – Mammal eye
AnalogyPenguin flipper – Dolphin flipper
AnalogyPotato (stem) – Sweet potato (root)
Natural selectionPeppered moth (Industrial melanism)
Pollution indicatorLichens
Anthropogenic evolutionAntibiotic-resistant bacteria, pesticide-resistant insects, herbicide-resistant weeds

These definitions, facts, and examples cover the high-yield NCERT points that are frequently tested in CBSE Class 12 Board examinations.

CBSE Class 12 Biology – Industrial Melanism & Anthropogenic Evolution (NCERT Notes)

Important Definitions

1. Industrial Melanism

Definition: Industrial melanism is the increase in the frequency of dark-coloured (melanic) individuals in a population due to industrial pollution and natural selection.

2. Camouflage

Definition: Camouflage is the ability of an organism to blend with its surroundings to avoid detection by predators.

3. Anthropogenic Evolution

Definition: Evolution caused by human activities such as the excessive use of antibiotics, pesticides, and herbicides.

4. Stochastic Process

Definition: A stochastic process is a chance-based process in which evolution occurs due to random mutations and natural selection, not according to a predetermined plan.

Industrial Melanism (Peppered Moth) – Key Facts

Before Industrialisation

  • Tree trunks were covered with white-coloured lichens.
  • White-winged moths were well camouflaged.
  • Dark (melanic) moths were easily seen and eaten by predators.
  • White-winged moths were more numerous.

After Industrialisation

  • Industrial smoke and soot blackened tree trunks.
  • Lichens disappeared due to pollution.
  • White moths became easily visible to predators.
  • Dark (melanic) moths became better camouflaged.
  • Dark moths survived and reproduced more.
  • Their population increased.

In Rural (Unpolluted) Areas

  • Lichens remained abundant.
  • White moths continued to dominate.
  • Melanic moths remained fewer.

Why Are Lichens Called Pollution Indicators?

  • Lichens are highly sensitive to air pollution.
  • They do not grow in polluted areas.
  • Presence of lichens indicates clean air.

CBSE One-liner:
Lichens are natural indicators of industrial air pollution.

Significance of Industrial Melanism

  • Best example of Natural Selection.
  • Demonstrates Evolution in action.
  • Shows that organisms with favourable adaptations survive and reproduce.

Antibiotic Resistance

Important Facts

  • Excessive use of antibiotics kills sensitive bacteria.
  • Resistant bacteria survive.
  • Resistant bacteria multiply rapidly.
  • Over time, resistant strains become common.

Example: Antibiotic-resistant bacteria.

Herbicide and Pesticide Resistance

Herbicides

  • Kill susceptible weeds.
  • Resistant weeds survive and reproduce.

Pesticides

  • Kill susceptible insects.
  • Resistant insects survive and multiply.

Anthropogenic Evolution

Definition

Evolution resulting from human activities.

Examples

  • Antibiotic-resistant bacteria
  • Pesticide-resistant insects
  • Herbicide-resistant weeds
  • Drug-resistant parasites

Important NCERT Statements

  • Better-adapted organisms survive and increase in number.
  • No variant is completely wiped out.
  • Evolution can occur within months or years.
  • Human activities accelerate natural selection.
  • Evolution is not a directed process.
  • Evolution is based on chance mutations and natural selection.

CBSE One-Mark Facts

  • Industrial melanism is evidence of natural selection.
  • Dark moths survived after industrialisation.
  • White moths survived before industrialisation.
  • Lichens are indicators of air pollution.
  • Camouflage helps organisms escape predators.
  • Excessive antibiotics lead to antibiotic resistance.
  • Excessive pesticides lead to pesticide resistance.
  • Excessive herbicides lead to herbicide-resistant weeds.
  • Evolution caused by humans is called anthropogenic evolution.
  • Evolution is a stochastic (chance-based) process.
  • Mutation provides variation, while natural selection acts on that variation.

Flow Chart (Very Important for Board Exams)

Before Industrialisation

  • White lichens on trees → White moths camouflaged → White moths survive → White moth population increases

⬇️

After Industrialisation

  • Smoke and soot blacken trees → Lichens disappear → Dark moths camouflaged → Dark moths survive → Dark moth population increases

⬇️

Conclusion

  • Natural Selection → Industrial Melanism → Evolution

Most Important CBSE Keywords

  • Industrial melanism
  • Natural selection
  • Camouflage
  • Lichens
  • Air pollution indicator
  • Antibiotic resistance
  • Pesticide resistance
  • Herbicide resistance
  • Anthropogenic evolution
  • Chance mutation
  • Stochastic process
  • Survival of the better-adapted organisms

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