Evolution — Class 10 Science (CBSE) explained

What you’ll learn

1. 1

   Lesson 1: Variation, Selection and Inheritance

   5 min
   • Variation Provides the Starting Point
   • Green Colour Gives a Survival Advantage
   • Chance Can Change a Small Population
   • Evolution Changes Inherited Trait Frequencies
   • An Environmental Change Need Not Be Evolution
   • Lifetime Experiences Do Not Alter Inheritance
   • Charles Darwin: Voyage and Natural SelectionNot assessed
2. 2

   Lesson 2: From the Origin of Life to New Species

   5 min
   • How Life Began Is a Different QuestionNot assessed
   • Early-Earth Conditions and Organic CompoundsNot assessed
   • Changing Traits Is Not Yet a New Species
   • Isolated Populations Become More Different
   • When Two Populations Cannot Reproduce Together
   • Does Isolation Matter Equally in Every Organism?
3. 3

   Lesson 3: Evidence for Evolutionary Relationships

   6 min
   • Classification Uses a Hierarchy of Characteristics
   • More Shared Characteristics Mean Closer Relationships
   • A Shared Limb Design Can Have Different Functions
   • The Same Function Does Not Prove the Same Origin
   • Fossils Preserve Evidence of Past Life
   • Depth and Isotope Ratios Help Estimate Age
   • Older Fossils Lie Beneath Later Deposits
4. 4

   Lesson 4: Evolution by Stages and Human Evolution

   7 min
   • An Intermediate Eye Can Still Be Useful
   • A Feature Can Become Useful for a New Function
   • Different Vegetables from Wild Cabbage
   • DNA Differences Help Trace Relationships
   • Evolution Does Not Rank Species as Better
   • Human Diversity Belongs to One Species
   • Shared African Origins and a Complex Migration
   • Recap: Explain Changes, Relationships and Evidence

Key concepts

The essence of evolution

What unites the two situations is a change in the frequency of an inherited trait.

Acquired and inherited traits

Germ cells in sexually reproducing organisms are made in specialised reproductive tissue. A change in non-reproductive tissue cannot be passed on to the DNA of these germ cells.

Micro-evolution and gene flow

The beetle changes so far are micro-evolution. They change common characteristics within a species.

Geographical isolation

Green colour is not selected at the first site, but is strongly selected where crows remain abundant.

Classification and ancestry

A closer relationship means a more recent common ancestor.

Homologous characteristics

The shared design is inherited from a common ancestor.

Molecular evidence

Changes in DNA during reproduction are basic events in evolution. Comparing DNA from different species therefore helps estimate how much it changes during their formation.

Evolution without a progress ladder

Nor is the new species automatically better. Evolution generates diversity and shapes it through environmental selection.

Exam focus

School assessment only

For 2026-27, CBSE assesses this topic in school (periodic assessment or portfolio), not in the year-end board examination. It is still worth learning: it builds on and supports the board chapters.

Syllabus

Evolution: formative assessment only this session; CBSE reading material provided.

Not assessed

These parts go beyond the 2026-27 syllabus and are taught for understanding only: Charles Darwin: Voyage and Natural Selection, How Life Began Is a Different Question and Early-Earth Conditions and Organic Compounds.

Exam note

Formative-only: assessed in school, not in the year-end board examination.

Practice in the app

81 board-pattern questions with marking schemes: 23 multiple choice (1 mark), 11 assertion–reason (1 mark), 16 very short answer (2 marks), 17 short answer (3 marks), 5 long answer (5 marks) and 9 case-based (4 marks).

Sample questions with marking points

Board-pattern questions from the AI Lessons practice set for this chapter. The marking points show what an examiner looks for; full model answers are in the app.

1. Very short answer2 marks

   A student argues that Bird and Human limbs cannot show common ancestry because their present uses differ. Give two points to correct this argument.

   Marking points

   • Bird and Human limbs share a similar basic structure inherited from a common ancestor.1
   • The shared structure can be modified for different functions; different uses do not rule out homology.1

2. Short answer3 marks

   A river separates two beetle sub-populations. Explain why separation alone need not mean that two species already exist, and describe how the populations could eventually become separate species.

   Marking points

   • Geographical separation reduces gene flow but does not by itself establish reproductive incompatibility.1
   • Genetic drift and different natural selection pressures can accumulate differences over generations.1
   • Separate species arise when members cannot reproduce with one another even if they meet.1

3. Long answer5 marks

   Explain how classification reflects evolutionary relationships. Use the limbs of Frog, Lizard, Bird and Human as evidence, and contrast this evidence with the wings of bats and birds. Include the relevant structures, functions and conclusions about ancestry.

   Marking points

   • More shared characteristics indicate closer relationships and more recent common ancestry; classification reflects these relationships.1
   • The limbs of Frog, Lizard, Bird and Human share a similar basic structure modified for different functions.1
   • These homologous limb structures indicate inheritance from a common ancestor.1
   • Bat wings are skin folds stretched mainly between elongated fingers.0.5
   • Bird wings have a feathery covering along the arm.0.5
   • Bird and bat wings are analogous: their common flying function but different wing origins does not by itself establish close relatedness.1

Frequently asked questions

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