Evolution is one of the most important and conceptual chapters in Class 12 Biology. Questions from this chapter are frequently asked in CBSE Board Exams, NEET, CUET, and other competitive examinations. The chapter explains how life originated on Earth and how organisms have changed gradually over millions of years to form the present diversity of life.

These Class 12 Evolution Notes PDF are prepared strictly according to the latest NCERT syllabus, covering all important theories, principles, diagrams, and examples. The notes are written in simple English, making them easy to understand for students. These notes are ideal for quick revision, concept clarity, and exam-oriented preparation.

Table of Contents

Class 12 Evolution Notes PDF | Complete Biology Chapter 7

Chapter Overview: Evolution (Class 12 Biology)

Evolution refers to the gradual change in organisms over a long period of time, leading to the formation of new species from pre-existing ones. It explains biodiversity and the relationships among living organisms.

1. Origin of Life

The origin of life is the process by which living organisms first appeared on Earth.

Special Creation Theory

Life was created by a supernatural power.
All organisms appeared in their present form.
This theory has no scientific evidence and is not accepted today.

Spontaneous Generation Theory

Life originated from non-living matter spontaneously.
Example: maggots from decaying meat.
This theory was disproved by Louis Pasteur.

Biogenesis Theory

Life originates only from pre-existing life.
Supported by experiments of Redi, Spallanzani, and Pasteur.

Chemical Evolution (Oparin–Haldane Theory)

Proposed by A.I. Oparin and J.B.S. Haldane.
Life originated from non-living organic molecules.
Early Earth atmosphere was reducing (CH₄, NH₃, H₂, H₂O).
Formation of complex organic molecules led to first life forms.

Miller–Urey Experiment

Conducted in 1953 by Stanley Miller and Harold Urey.
Simulated early Earth conditions.
Demonstrated formation of amino acids from inorganic substances.
Provided strong evidence for chemical evolution.

2. Evolution of Life Forms – A Theory

Evolution occurs through genetic variations that accumulate over generations and lead to the formation of new species.

3. Evidences for Evolution

a) Morphological and Anatomical Evidence

Homologous organs show common ancestry.
Example: Forelimbs of humans, whales, bats.

b) Analogous Organs

Same function but different origin.
Example: Wings of birds and insects.

c) Vestigial Organs

Reduced and non-functional organs.
Example: Appendix, coccyx, wisdom teeth.

d) Embryological Evidence

Early embryos of vertebrates are similar.
Indicates common ancestry.

e) Fossil Evidence

Fossils are preserved remains of ancient organisms.
Fossil records show gradual evolution.
Example: Evolution of horse.

f) Molecular Evidence

Similarities in DNA, RNA, and proteins.
Cytochrome c comparison supports evolution.

4. Darwin’s Theory of Natural Selection

Proposed by Charles Darwin in his book On the Origin of Species (1859).

Main Points

Overproduction of offspring
Limited resources
Struggle for existence
Variation among individuals
Survival of the fittest
Natural selection
Origin of new species

Limitations

Did not explain the origin of variations.
Did not include genetics.

5. Lamarckism

Proposed by Jean Baptiste Lamarck.

Main Concepts

Use and disuse of organs
Inheritance of acquired characters

Example

Long neck of giraffe due to stretching.

❌ Lamarckism is not accepted because acquired characters are not inherited.

6. Mutation Theory

Proposed by Hugo de Vries.

Evolution occurs due to sudden changes (mutations).
Based on experiments on Oenothera lamarckiana.
Mutations provide raw material for evolution.

7. Hardy–Weinberg Principle

Proposed by G.H. Hardy and Wilhelm Weinberg.

Statement

The frequency of alleles in a population remains constant from generation to generation in the absence of evolutionary forces.

Equation


p^2 + 2pq + q^2 = 1

Where:

p = frequency of dominant allele
q = frequency of recessive allele

Factors Affecting Genetic Equilibrium

Mutation
Gene migration (gene flow)
Genetic drift
Natural selection
Recombination

8. Adaptive Radiation

Evolution of different species from a common ancestor.
Example: Darwin’s finches on Galapagos Islands.
Leads to diversification.

9. Biological Evolution

Biological evolution refers to changes in allele frequencies in a population over time.

Genetic Drift

Random change in gene frequency.
More prominent in small populations.
Example: Founder effect, Bottleneck effect.

10. Speciation

Formation of new species due to:

Geographical isolation
Reproductive isolation
Genetic variations
Natural selection

11. Human Evolution

Major Stages

Dryopithecus
Ramapithecus
Australopithecus
Homo habilis
Homo erectus
Homo neanderthalensis
Homo sapiens

Key Points

Human evolution began in Africa.
Brain size increased gradually.
Use of tools and language developed.

12. Evolution and Classification

Taxonomy is based on evolutionary relationships.
Closely related organisms share more similarities.
Molecular taxonomy supports evolution.

13. Evolution vs Creationism

Evolution is supported by scientific evidence.
Creationism lacks experimental proof.
Modern biology accepts evolution as the basis of diversity.

Why These Class 12 Evolution Notes PDF Are Important

Fully NCERT based
Covers board + NEET questions
Includes definitions, theories, examples
Useful for revision and exams
Ideal for PDF download and website content

Conclusion

The chapter Evolution explains the origin of life, diversity of organisms, and the scientific basis of biological changes over time. Understanding this chapter helps students connect concepts from genetics, ecology, and molecular biology. These Class 12 Evolution Notes PDF provide a complete and reliable resource for students aiming to score high in exams.

Class 12 Biology Evolution Important Questions (Repeated & Most Searched)

🔥 Very Short Answer Questions (1 Mark)

What is evolution?
Name the scientists who proposed the Chemical Evolution Theory.
Which experiment supports chemical evolution?
What is a fossil?
Name one vestigial organ in humans.
Define homologous organs.
Define analogous organs.
Who proposed the theory of natural selection?
What is adaptive radiation?
Write the Hardy–Weinberg equation.

⭐ Short Answer Questions (2–3 Marks)

(Most Repeated in Board Exams)

Explain the biogenesis theory of origin of life.
What is chemical evolution? Mention the role of early Earth atmosphere.
Differentiate between homologous and analogous organs.
What are vestigial organs? Give two examples.
State two evidences from fossils that support evolution.
Write any two limitations of Darwin’s theory of natural selection.
What is genetic drift? Mention its significance.
Define mutation and explain its role in evolution.
What is gene flow? How does it affect evolution?
What is natural selection?

🔥 Long Answer Questions (4–5 Marks)

(Highly Repeated & Search Trending)

1. Describe the Oparin–Haldane theory of origin of life.

Explain the steps involved in chemical evolution with examples.

2. Describe the Miller–Urey experiment.

Aim of the experiment
Experimental setup
Conclusion
Significance

3. Explain Darwin’s theory of natural selection.

Mention its major postulates and limitations.

4. Describe various evidences of evolution.

Explain:

Morphological evidence
Anatomical evidence
Fossil evidence
Molecular evidence

5. Explain the Hardy–Weinberg principle.

State the principle
Write the equation
Factors affecting genetic equilibrium

6. What is adaptive radiation?

Explain with reference to Darwin’s finches.

7. Describe the process of speciation.

Explain the role of:

Isolation
Mutation
Natural selection
Genetic drift

8. Describe human evolution with the help of a flowchart.

Mention important evolutionary stages.

📌 Assertion–Reason Questions

Assertion: Homologous organs indicate evolution.
Reason: They have same origin but different functions.
Assertion: Genetic drift is more effective in small populations.
Reason: Random changes have greater impact in small populations.
Assertion: Analogous organs do not indicate common ancestry.
Reason: They have same function but different origin.

🧠 Case-Based Questions (New Pattern – Boards & CUET)

Case 1:

A population of beetles shows change in colour frequency over generations due to environmental changes.

Questions: a) Name the evolutionary mechanism involved.
b) What type of selection is this?
c) Define allele frequency.

📊 Diagram-Based Questions (Very Important)

Diagram of Miller–Urey Experiment
Evolution of Horse (Fossil sequence)
Human Evolution Chart
Structure showing Homologous organs

👉 These diagrams are compulsory for board exams.

🔍 Most Searched Questions by Students (Google Trends)

Is Lamarckism accepted today? Explain why.
Difference between Natural Selection and Genetic Drift
Explain Founder Effect and Bottleneck Effect
Why are fossils considered strong evidence of evolution?
Short note on Molecular evolution

✅ NEET-Focused MCQ Practice (Trending)

Which gas was absent in early Earth atmosphere?
Who disproved spontaneous generation?
Example of adaptive radiation is found in?
Which principle explains genetic equilibrium?
Which organ is vestigial in humans?

⭐ Why These Questions Are Important?

Repeated in CBSE Board Exams
Asked in NEET, CUET & State Boards
Based on NCERT lines
Frequently searched by students
Helpful for last-minute revision

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