write short note on the Darwin's theory of natural selection.
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Charles Robert Darwin in his book ‘Origin of species’ by Natural selection gave a beautiful theory on evolution. His theory of Natural selection can be summarized as follows:
1. Overproduction (Enormous fertility)
2. Struggle for existence
3. Survival of the fittest
4. Variation and heredity
5. Origin of new species
Overproduction:
All the plants and animals have tendency to reproduce a large number of offsprings. For example, an oyster lays 60-80 million eggs and a salmon 28,000,000 eggs in a year. It seems that if this number is not checked the earth would have been overcrowded with only one or the other kind of organisms. And actually we see the numbers of organisms are checked by some natural laws.
Struggle for Existence:
The size of population increases rapidly but amount of food and space remains constant. According to Darwin, there is an intense desire among organisms for food, land, mate, etc. to ensure living. This struggle is of three types.
(i) Intraspecific Struggle:
Since the requirement of individuals of a species is same they compete among themselves.
(ii) Interspecific Struggle:
Individuals of different species living together also compete among themselves. Moreover, carnivorous habit of a species causes death of other species.
(iii) Struggle with Inanimate Nature:
In unfavourable conditions like flood, cyclone, earthquake, draught, etc. struggle for existence becomes more severs. Organisms simply have to coup with or bear these hardships of the nature.
Variations, Heredity and Survival of the Fittest:
In those entire struggles the individuals which are better equipped survive. Due to variation and heredity, individuals vary among themselves. So these individuals with better variation have a better chance to survive and give rise to offsprings to suit to changed conditions. Individuals with weak charcters perish or have no chance in evolution.
Natural Selection:
From above facts it appears that nature weighs in the balance and selects better ones eliminating unwanted variants. Nature does not show favour to anybody. Darwin explained long-neck giraffe had a better chance to survive over their short-necked kins.
Origin of New Species:
Darwin concluded that new species originate by natural selection. He summarized that due to struggle for existence, variations and inheritance the offsprings of successive generations are better adapted for the next phase of struggle.Darwin called it descent with modification. As the environment is ever changing, it demands new variations in the organisms. So that gradually new characters are accumulated in the offsprings generation after generations. Hence after a long-run the offspring will vary in a greater way from their original ancestors and can be called a new species.
1. Overproduction (Enormous fertility)
2. Struggle for existence
3. Survival of the fittest
4. Variation and heredity
5. Origin of new species
Overproduction:
All the plants and animals have tendency to reproduce a large number of offsprings. For example, an oyster lays 60-80 million eggs and a salmon 28,000,000 eggs in a year. It seems that if this number is not checked the earth would have been overcrowded with only one or the other kind of organisms. And actually we see the numbers of organisms are checked by some natural laws.
Struggle for Existence:
The size of population increases rapidly but amount of food and space remains constant. According to Darwin, there is an intense desire among organisms for food, land, mate, etc. to ensure living. This struggle is of three types.
(i) Intraspecific Struggle:
Since the requirement of individuals of a species is same they compete among themselves.
(ii) Interspecific Struggle:
Individuals of different species living together also compete among themselves. Moreover, carnivorous habit of a species causes death of other species.
(iii) Struggle with Inanimate Nature:
In unfavourable conditions like flood, cyclone, earthquake, draught, etc. struggle for existence becomes more severs. Organisms simply have to coup with or bear these hardships of the nature.
Variations, Heredity and Survival of the Fittest:
In those entire struggles the individuals which are better equipped survive. Due to variation and heredity, individuals vary among themselves. So these individuals with better variation have a better chance to survive and give rise to offsprings to suit to changed conditions. Individuals with weak charcters perish or have no chance in evolution.
Natural Selection:
From above facts it appears that nature weighs in the balance and selects better ones eliminating unwanted variants. Nature does not show favour to anybody. Darwin explained long-neck giraffe had a better chance to survive over their short-necked kins.
Origin of New Species:
Darwin concluded that new species originate by natural selection. He summarized that due to struggle for existence, variations and inheritance the offsprings of successive generations are better adapted for the next phase of struggle.Darwin called it descent with modification. As the environment is ever changing, it demands new variations in the organisms. So that gradually new characters are accumulated in the offsprings generation after generations. Hence after a long-run the offspring will vary in a greater way from their original ancestors and can be called a new species.
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