1. Mechanism of Evolution
Mechanism of evolution explains:
- How variation arises.
- How new species (speciation) are formed.
2. Origin of Variation
Variation is the raw material of evolution.
Variation arises due to:
- Mutation
- Genetic recombination
- Gene flow
- Genetic drift
NCERT emphasis (this section): Mutation
3. Hugo de Vries
- Dutch botanist.
- Worked on Evening Primrose (Oenothera lamarckiana).
- Proposed the Mutation Theory of Evolution.
4. Mutation
Mutation is:
A sudden, random, heritable change in the genetic material.
Characteristics:
- Random
- Directionless
- Sudden
- Heritable
5. Mutation Theory
According to Hugo de Vries:
- Evolution occurs because of mutations.
- New species may arise through large mutations.
- Evolution can occur suddenly, not gradually.
6. Saltation
Saltation means:
Evolution by a single large mutation.
This was proposed by Hugo de Vries.
7. Darwin vs Hugo de Vries
| Darwin | Hugo de Vries |
|---|---|
| Evolution is gradual | Evolution is sudden |
| Small heritable variations | Large mutations |
| Natural selection is the main force | Mutation is the main force |
| Directional variation | Random mutation |
| Slow evolution | Saltation (single-step evolution) |
8. Darwin’s View
Darwin believed:
- Small inherited variations accumulate over generations.
- Natural selection acts on these variations.
- Evolution is slow and gradual.
9. Mutation Characteristics
Mutation is:
- Sudden
- Random
- Heritable
- Directionless
It may be:
- Beneficial
- Harmful
- Neutral
10. Speciation
Speciation is:
Formation of a new species from an existing species.
It occurs due to:
- Accumulation of variations
- Natural selection
- Mutation
- Reproductive isolation (covered later in NCERT)
One-Mark Questions
Q1. Who proposed the Mutation Theory?
Answer: Hugo de Vries.
Q2. On which plant did Hugo de Vries work?
Answer: Evening Primrose (Oenothera lamarckiana).
Q3. What is mutation?
Answer: A sudden, random, heritable change in genetic material.
Q4. What is saltation?
Answer: Evolution by a single large mutation.
Q5. According to Darwin, evolution is ________.
Answer: Gradual.
Q6. According to Hugo de Vries, evolution occurs by ________.
Answer: Mutation.
NCERT Keywords for Board Exams
- Mechanism of Evolution
- Mutation
- Hugo de Vries
- Evening Primrose
- Saltation
- Speciation
- Heritable Variation
- Natural Selection
- Gradual Evolution
- Random Mutation
Most Important NCERT Differences
| Darwin’s Theory | Mutation Theory (de Vries) |
|---|---|
| Small, heritable variations | Large, sudden mutations |
| Gradual evolution | Sudden evolution (saltation) |
| Natural selection drives evolution | Mutation drives evolution |
| Variations are selected over time | New species may arise in one major step |
Board Exam Tip
Remember these four high-yield facts:
- Mutation Theory was proposed by Hugo de Vries.
- He worked on Evening Primrose (Oenothera lamarckiana).
- Mutation is a random, sudden, heritable change.
- Saltation means evolution by a single large mutation.
Sarvan sir- Chemistry For All 