CBSE Class 12 Biology – Evolution of Life Forms (NCERT) Important Facts

Theory of Special Creation

According to religious literature:

  • All living organisms were created in their present form.
  • Species have remained unchanged since creation.
  • Earth is about 4000 years old.

CBSE Fact: These ideas were challenged during the 19th century.

Charles Darwin

  • Travelled around the world on H.M.S. Beagle.
  • Observed plants, animals, and fossils.
  • Proposed the Theory of Evolution by Natural Selection.

Important Observation

  • Living organisms show similarities with one another.
  • Present-day organisms also resemble extinct organisms.
  • Species have changed gradually over millions of years.

Evolution

Evolution is the gradual change in living organisms over long periods of time, leading to the formation of new species.

Variation

  • Every population has inherited variations.
  • Variations make individuals different from one another.
  • Variation is the raw material for evolution.

Natural Selection

Darwin proposed Natural Selection as the mechanism of evolution.

Principle

Individuals with favourable variations survive and reproduce more successfully.

This is also known as:

“Survival of the Fittest.”

Fitness (According to Darwin)

Fitness means reproductive fitness, not physical strength.

A fit organism:

  • Survives better.
  • Produces more offspring.
  • Passes favourable traits to the next generation.

Important Board Point: Fitness = Ability to leave more progeny.

Natural Selection Process

Variation
⬇
Competition
⬇
Survival of better-adapted individuals
⬇
More reproduction
⬇
Natural selection
⬇
Evolution

Alfred Russel Wallace

  • Worked in the Malay Archipelago.
  • Independently proposed the idea of Natural Selection.
  • Published similar conclusions around the same time as Darwin.

Extinction

  • Many organisms that lived millions of years ago no longer exist.
  • New species evolved while others became extinct.

Common Ancestor

  • All present-day organisms share common ancestors.
  • Different groups diverged over millions of years.

Geological and Biological History

NCERT states:

  • Geological history of Earth closely matches the biological history.
  • Evolution occurred over billions of years.

Important Keywords for Board Exams

  • Evolution
  • Natural Selection
  • Variation
  • Adaptation
  • Reproductive Fitness
  • Common Ancestor
  • Extinction
  • H.M.S. Beagle
  • Alfred Russel Wallace
  • Survival of the Fittest
  • Theory of Special Creation

Frequently Asked One-Mark Questions

Q1. Name the ship on which Darwin travelled.
Answer: H.M.S. Beagle

Q2. Who independently proposed Natural Selection besides Darwin?
Answer: Alfred Russel Wallace

Q3. What is meant by fitness according to Darwin?
Answer: Reproductive fitness (ability to leave more offspring).

Q4. What is the raw material of evolution?
Answer: Variation.

Q5. What is Natural Selection?
Answer: The process by which individuals with favourable variations survive and reproduce more successfully.

Q6. What does “Survival of the Fittest” mean?
Answer: Better-adapted individuals survive and produce more offspring.

NCERT Statements Often Asked in Boards

  • Evolution is a gradual process.
  • Variation exists in every population.
  • Natural selection is the mechanism of evolution.
  • Fitness refers to reproductive success.
  • All organisms share common ancestors.
  • Geological history correlates with biological history.
  • Earth is billions of years old, not thousands.

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