Answer: Darwin’s theory of natural selection.
Charles R. Darwin was a British biologist. He postulated the “Theory of origin of species by natural selection”.
Principles of Darwinism:
Darwin’s theory of organic evolution by natural selection is based on the following principles:
i. Over production or prodigality of production:
All organisms have a natural tendency to over produce.
If this tendency is not checked, then even a single species of a plant or animal will occupy the entire space available on the earth.
ii. Struggle for existence:
Organisms multiply in geometric ratio, but space and food remain constant leading to competition for survival. Increase in the number of species leads to a competition called struggle for existence.
iii. Variations and Heredity:
The differences which occur between the closely related organisms are called variations. It is universal law of nature. Variations may be favourable or unfavourable.
iv. Survival of the fittest or natural selection:
According to Darwin, in the struggle for existence, the fittest individuals survive and reproduce, while the unfit individuals perish.
v. Origin of new species:
According Darwin, useful variations appear in every generation and are inherited from one generation to another.
Objections to Darwin’s natural selection theory:
i. Natural selection theory explained “survival of the fittest” but not “arrival of the fittest”.
ii. Darwin did not take into account the hereditary principles.
iii. He could not provide a satisfactory explanation for the cause, origin and inheritance of variations.
iv. Certain useless characters are also inherited. He could not explain the inheritance of useless variations.
v. He was unable to differentiate variations as hereditary and environmental variations.
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