The theory of ‘natural selection’ for organic evolution was given by Charles Darwin in 1858 in his famous book ‘The Origin of Species’. This theory was widely accepted by various biologists.
The main postulates of Darwin’s theory of evolution are:
1. Rapid multiplication
All the animals and plants tend to increase their population, but the number of individuals of each species remains nearly constant naturally.
2. Competition and struggle for existence
This is due to the reason of competition and struggle between members of the same species and different species for food, space and other basic needs.
3. Variations
Within any population, there is a natural variation i.e. the individuals of same species vary in size, shape, behaviour and structure as compared to each other.
4. Natural selection or the survival of the fittest
In the struggle of existence, the individual who have more favourable variations will survive and others will perish. This sorting out of the individuals with useful variations by nature was called ‘natural selection’ by Darwin and ‘survival of the fittest’ by Wallace.
5. Inheritance of variations
The individuals after their natural selection pass on their useful variations to the next generations.
6. Formation of new species
These variations accumulate in new generations and after a number of generations these become so prominent that a new species with modified characters is formed.
Criticism
Though Darwin’s theory of evolution was widely accepted, but it was criticized on the ground that it could not explain how the variations arise in individuals of the same species.
Test Your Understanding and Answer These Questions:
- Explain Darwin’s theory of evolution.
- Write a short note on ‘struggle for existence’.
- Name the most accepted theory of evolution.
- What do you meant by natural selection?
- What do you meant by ‘survival of the fittest’.
- Name the book in which Darwin wrote his theory of evolution