What is Speciation? (NCERT Short Notes)

Introduction

Speciation is the process by which new species are formed from existing species over a long period of time. According to NCERT, speciation occurs when populations of the same species become different enough due to genetic changes, natural selection, and isolation that they can no longer interbreed and produce fertile offspring.

Definition of Speciation

Speciation is the evolutionary process through which one species splits into two or more new species.

It is one of the most important concepts in the study of evolution.

Why Does Speciation Occur?

Speciation occurs because organisms continuously adapt to their environment. Over time, differences accumulate among populations.

Main Causes of Speciation

Cause	Explanation
Genetic Variation	Differences in genes among individuals
Natural Selection	Survival of organisms with favorable traits
Geographical Isolation	Physical barriers separate populations
Reproductive Isolation	Populations can no longer interbreed
Genetic Drift	Random changes in gene frequencies

Genetic Variation and Speciation

What is Genetic Variation?

Genetic variation refers to differences in DNA among individuals of the same species.

Sources of Variation

Mutations
Sexual reproduction
Gene recombination
Chromosomal changes

Importance

Without variation, evolution and speciation cannot occur.

Role of Natural Selection

Natural Selection

Organisms with beneficial traits survive and reproduce more successfully.

Example

If a population of birds lives in different environments:

Birds with stronger beaks survive where hard seeds are available.
Birds with slender beaks survive where insects are abundant.

Over many generations, these differences become significant, leading to speciation.

Geographical Isolation

Definition

When populations are separated by physical barriers, it is called geographical isolation.

Common Barriers

Mountains
Rivers
Oceans
Deserts

Because separated populations cannot interbreed, they evolve independently.

Reproductive Isolation

What is Reproductive Isolation?

When two populations become unable to mate successfully and produce fertile offspring.

Importance

Reproductive isolation is considered the final stage of speciation.

Types

1. Prezygotic Isolation

Occurs before fertilization.

Examples:

Different mating seasons
Different mating behaviors
Physical incompatibility

2. Postzygotic Isolation

Occurs after fertilization.

Examples:

Hybrid offspring die early.
Hybrid offspring are infertile.

Types of Speciation

1. Allopatric Speciation

Occurs due to geographical isolation.

Features

Most common type
Physical barrier present
Populations evolve separately

Example

Different populations of squirrels separated by a canyon.

2. Sympatric Speciation

Occurs without geographical separation.

Features

Same geographical area
Genetic changes create reproductive isolation

Example

Some plant species develop different chromosome numbers.

Comparison of Allopatric and Sympatric Speciation

Feature	Allopatric Speciation	Sympatric Speciation
Physical Barrier	Present	Absent
Geographic Separation	Yes	No
Common in Animals	Yes	Less Common
Common in Plants	Moderate	High

Speciation According to NCERT Example

NCERT explains that populations separated geographically accumulate different variations.

As generations pass:

Variations arise.
Different environmental pressures act.
Populations adapt differently.
Reproductive isolation develops.
New species are formed.

Flowchart of Speciation

			
Genetic Variation
        ↓
Natural Selection
        ↓
Isolation
        ↓
Accumulation of Differences
        ↓
Reproductive Isolation
        ↓
New Species Formation

		

Importance of Speciation

Ecological Importance

Increases biodiversity
Creates new adaptations
Helps organisms survive changing environments

Evolutionary Importance

Drives evolution
Produces new species
Explains biological diversity on Earth

Examples of Speciation

Darwin’s Finches

Charles Darwin observed finches with different beak shapes on islands. Over time, these populations evolved into distinct species.

Galápagos Island Species

Different environmental conditions caused isolated populations to evolve separately.

Plant Speciation

Many plant species arise through chromosome number changes.

Key Points to Remember

Speciation is the formation of new species.
It is a major outcome of evolution.
Genetic variation is the raw material for speciation.
Natural selection favors beneficial variations.
Geographical isolation often initiates speciation.
Reproductive isolation completes speciation.
Allopatric speciation involves physical separation.
Sympatric speciation occurs without physical separation.
Speciation increases biodiversity.

Practice Questions

Very Short Answer Questions

Q1. What is speciation?

Answer: Speciation is the process of formation of new species from existing species.

Q2. What is geographical isolation?

Answer: Separation of populations by physical barriers such as mountains, rivers, or oceans.

Q3. What is genetic variation?

Answer: Differences in genes among individuals of a population.

Q4. Name the most common type of speciation.

Answer: Allopatric speciation.

Q5. Which process provides raw material for evolution?

Answer: Genetic variation.

Fill in the Blanks

Speciation is the formation of new ________.
Answer: species
Physical barriers cause ________ isolation.
Answer: geographical
Variations arise due to changes in ________.
Answer: genes
Natural selection was proposed by ________.
Answer: Charles Darwin
Reproductive isolation is the final stage of ________.
Answer: speciation

Multiple Choice Questions (MCQs)

1. Speciation refers to:

A. Extinction of species
B. Formation of new species
C. Migration of species
D. Classification of species

✅ Answer: B

2. Which factor is essential for speciation?

A. Photosynthesis
B. Respiration
C. Genetic Variation
D. Digestion

✅ Answer: C

3. Physical separation of populations causes:

A. Mutation
B. Isolation
C. Respiration
D. Nutrition

✅ Answer: B

4. Which scientist is associated with natural selection?

A. Mendel
B. Pasteur
C. Darwin
D. Hooke

✅ Answer: C

5. Allopatric speciation occurs due to:

A. Pollution
B. Climate only
C. Geographical isolation
D. Nutrition

✅ Answer: C

6. Sympatric speciation occurs:

A. With physical barriers
B. Without geographical separation
C. Only in animals
D. Only in humans

✅ Answer: B

7. Which is a source of genetic variation?

A. Mutation
B. Digestion
C. Excretion
D. Breathing

✅ Answer: A

8. Reproductive isolation means:

A. Populations can interbreed freely
B. Populations cannot produce fertile offspring together
C. Populations migrate together
D. Populations share habitat

✅ Answer: B

9. Speciation contributes to:

A. Biodiversity
B. Soil erosion
C. Water pollution
D. Deforestation

✅ Answer: A

10. Darwin’s finches are an example of:

A. Extinction
B. Artificial selection
C. Speciation and adaptive evolution
D. Respiration

✅ Answer: C

Conclusion

Speciation is the evolutionary process through which new species arise from existing species. According to NCERT, genetic variation, natural selection, isolation, and reproductive isolation work together over many generations to create new species. Speciation is responsible for the immense biodiversity found on Earth today.

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