Evolution – Class 12 Biology Notes | CBSE NCERT Based

 🧬 Chapter 7: Evolution – Class 12 Biology Notes


🔹 Introduction


Evolution refers to the gradual changes occurring in living organisms over millions of years. It explains the origin of new species from pre-existing ones through various mechanisms like mutation, natural selection, genetic drift, etc.



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🔹 Origin of Life


Big Bang Theory: Universe originated about 20 billion years ago.


Early Earth: Formed around 4.5 billion years ago; no oxygen, only methane, ammonia, hydrogen, water vapor.


Chemical Evolution: Life began from non-living molecules (Oparin-Haldane theory).


Miller-Urey Experiment: Simulated early Earth conditions and created organic molecules (amino acids).



📌 Important Diagram: Miller and Urey's Experiment Setup



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🔹 Theories of Evolution


1. Lamarckism:


Proposed by Jean Baptiste Lamarck.


Theory of Inheritance of Acquired Characters.


Example: Giraffe's long neck.



2. Darwinism (Natural Selection):


Proposed by Charles Darwin.


Survival of the fittest.


Based on:


Variation


Overproduction


Struggle for existence


Survival and reproduction




📌 Important Diagram: Darwin's Finches



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🔹 Modern Synthetic Theory (Neo-Darwinism)


Combines Darwin’s natural selection with modern genetics:


Mutation


Genetic recombination


Natural selection


Genetic drift


Isolation




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🔹 Evidence of Evolution


1. Paleontological Evidence: Fossils (e.g., Archaeopteryx)


2. Comparative Anatomy:


Homologous organs (same origin, different function): e.g., forelimbs of vertebrates.


Analogous organs (different origin, same function): e.g., wings of bat and bird.



3. Embryological Evidence


4. Molecular Evidence: DNA and protein similarities


📌 Important Diagram: Homologous vs Analogous Organs



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🔹 Adaptive Radiation


Evolution from a common ancestor into different forms to adapt to different environments.


Example: Darwin’s finches on Galápagos Islands.



📌 Important Diagram: Adaptive Radiation in Finches



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🔹 Evolution by Natural Selection (Industrial Melanism)


Example: Biston betularia moths in England.


White moths replaced by black moths during industrial pollution.




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🔹 Hardy-Weinberg Principle


States allele frequencies in a population remain constant in the absence of evolutionary forces.


Formula: p² + 2pq + q² = 1



📌 Important Diagram: Hardy-Weinberg Genetic Equilibrium Graph



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🔹 Mechanisms of Evolution


Mutation


Gene flow


Genetic drift (Founder effect, Bottleneck effect)


Natural selection




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🔹 Speciation


Formation of new species.


Types: Allopatric and Sympatric speciation.




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🔹 Human Evolution


Primates evolved ~15 mya.


Homo habilis (2 mya), Homo erectus (1.5 mya), Neanderthals, and Homo sapiens.


Modern humans originated in Africa ~200,000 years ago.



📌 Important Diagram: Evolution of Man Chart



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✍️ Summary


Concept Key Point


Origin of Life Chemical evolution via Miller-Urey e

xperiment

Darwinism Natural selection, survival of fittest

Evidence Fossils, anatomy, embryology, molecular

Human Evolution From primates to modern man over 15 million years


📌 Important Diagram Names for Evolution Chapter:


1. Miller-Urey Experiment Setup

→ To show chemical origin of life.



2. Darwin’s Finches

→ To explain adaptive radiation.



3. Homologous and Analogous Organs Comparison

→ To understand anatomical evidence of evolution.



4. Hardy-Weinberg Equilibrium Graph

→ Shows genetic stability and factors affecting evolution.



5. Industrial Melanism in Moths

→ Example of natural selection.



6. Human Evolution Timeline / Chart

→ Shows primate evolution up to Homo sapiens.



7. Adaptive Radiation in Australian Marsupials (Optional)

→ To extend concept of adaptive radiation beyond finches.



8. Speciation Process Diagram (Allopatric & Sympatric)

→ 

To show how new species evolve.


✍️ Written by: Shahid – Study with Shahid


📎 Visit for more free Class 12 Notes:

👉 https://shahidnotes12.blogspot.com


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