🌍 Evolution of Life

1. Origin of Earth & Life

  • Earth formed about 4.54 billion years ago.
  • Life originated around 4.0 billion years ago.
  • Most accepted theory: Oparin–Haldane Theory.

2. Oparin–Haldane Theory (Chemical Evolution)

  • Life originated from non-living matter through physico-chemical processes.
  • Sequence:
    • Atoms → Molecules → Organic compounds → Macromolecules → First cells
  • Called chemical evolution or abiogenesis.
  • Possible only under primitive Earth conditions (not today).

3. Chemical Evolution (Chemogeny)

(i) Atomic Phase

  • Early Earth had elements: H, O, C, N, S, P
  • Distribution:
    • Heavy → core (Fe, Ni)
    • Medium → crust (Na, Mg, Si)
    • Light → atmosphere (H, O, N, C)

(ii) Formation of Inorganic Molecules

  • Examples:
    • H₂, N₂, H₂O, CH₄, NH₃, CO₂
  • First molecules likely:
    • Water (H₂O)
    • Ammonia (NH₃)

(iii) Formation of Organic Molecules

  • Simple molecules formed:
    • Sugars, amino acids, fatty acids, nitrogen bases
  • Energy sources:
    • UV rays, lightning, heat
  • No ozone layer → high radiation

Prebiotic Soup

  • Oceans contained organic molecules → called “hot dilute soup”
  • Molecules accumulated → formed coacervates (primitive cell-like structures)

4. Miller–Urey Experiment (1953)

  • Proved organic molecules can form abiotically.

Setup:

  • Gases used: CH₄, NH₃, H₂, H₂O
  • Electric sparks (simulating lightning)

Result:

  • Formation of amino acids:
    • Glycine, Alanine, Aspartic acid

👉 Conclusion: Building blocks of life formed naturally on early Earth.

5. Evolution of Cells

  • First life: Prokaryotes (~3.8 billion years ago)
    • Initially heterotrophic → later autotrophic
  • Eukaryotes (~2 billion years ago) evolved later

🌱 Biological Evolution (Organic Evolution)

Definition

  • Gradual change in organisms over generations from common ancestors.

Main Theories of Evolution

I. Lamarckism (Inheritance of Acquired Characters)

Scientist: Jean-Baptiste Lamarck
Book: Philosophie Zoologique (1809)

Key Ideas:

  • Use & disuse of organs
  • Acquired traits are inherited
  • Environmental influence

Examples:

  • Giraffe’s long neck
  • Webbed feet in aquatic birds
  • Loss of limbs in whales

II. Darwinism (Natural Selection)

Scientist: Charles Darwin
Book: On the Origin of Species (1859)

Key Concepts:

  1. Variation
  2. Overproduction
  3. Struggle for existence:
    • Intraspecific
    • Interspecific
    • Environmental
  4. Survival of the fittest
  5. Inheritance of useful traits

Neo-Darwinism (Modern Synthetic Theory)

Combines Darwin + Genetics

Key factors:

  • Mutation
  • Recombination
  • Heredity
  • Natural selection
  • Isolation

III. Mutation Theory

Scientist: Hugo de Vries
Book: Mutation Theory (1901)

Key Points:

  • Evolution occurs via sudden mutations
  • Mutations are:
    • Heritable
    • Random
  • Useful mutations → selected
  • Harmful → eliminated

🦴 Important Evolutionary Facts

Archaeopteryx

  • Connecting link between reptiles and birds
  • Features:
    • Wings (bird-like)
    • Teeth & tail (reptile-like)
  • Lived ~150 million years ago
  • Found in Germany

Dinosaurs

  • Lived in Mesozoic Era (252–66 million years ago)
  • Known as Age of Reptiles

Periods:

  1. Triassic
  2. Jurassic
  3. Cretaceous

Cro-Magnon (Early Humans)

  • Lived ~35,000–45,000 years ago
  • Brain capacity: ~1600 cc
  • Features:
    • Strong body
    • Large brain
  • Considered ancestors of modern humans (Homo sapiens)

📌 Quick Summary

  • Life began via chemical evolution.
  • First cells were prokaryotic.
  • Evolution driven by:
    • Natural selection
    • Mutation
    • Genetic variation
  • Evidence from fossils and transitional forms.

FAQs

1. Which gases was absent in the atmosphere of the primitive earth :- Oxygen

2. According to recent proof, the life on earth emerged approximately :- Before 2,000,000,000 years

3. Which is the oldest organism on earth :- Blue-green algae

4. The book, The Origin of Species was written by :- Darwin

5. Darwin’s theory of natural selection is based on –

(a) Overproduction    (b) Struggle for existence and variation     (c) Survival of the fittest     

Ans. (d) All of the above

6. Who propounded the theory of evolution :- Darwin

7. Who explained first the evolution of life :- Lamarck

8. The mutation theory of evolution was enunciated by :- Hugo de Vries

9. Match List-I with List-II and select the correct answer using the codes given below/the lists :

 List-I                                                                      List-II

 A. Theory of mutation                                1. De Vries 

 B. Theory of evolution                                2. Darwin 

 C. One gene one enzyme hypothesis       3. Beadle and Tatum

 D. Operon concept                                      4. Jacob and Monod

 Ans :- 1 2 3 4

10. The main factor of evolution is :– Natural selection

11. In the context of organic evolution, the loss of limbs in snakes is explained by the phenomenon of :– Use and disuse of organs

12. The reason of large-scale diversity among the organisms is :– Mutation

13. Among living organisms, which is the most responsible factor for bringing about the origin of a new species :- Mutation

14. Latest ancestor of modern human is :- Cro-Magnon man

15. Archaeopteryx is :– Most ancient bird of jurassic age

16. ‘Archaeopteryx’ is a connecting link between which classes of animal :- Reptilia and Aves

17. Mammoth is the ancestor of :– Elephant

18. Dinosaurs were :– Mesozoic reptiles

19. With reference to the evolution of living organisms, which sequences is correct?

Ans :-  Salamander-Python-Kangaroo 

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