What is Neodarwinism?
As the theory of natural selection proposed by Darwin had many inaccuracies, by the year 1890 doubts began to arise as to its usefulness. Around the year 1910 many critics opined that Darwin theory of selection is purely speculative. With the discovery of mutations by de Vries it proposed that evolution proceeded by was large jumps and not by accumulation of minor variations.
The contribution of Mendel (even though he was unaware) provided the necessary proof to Darwin’s concept regarding the origin of heritable variations not necessarily by means of mutation. Mendle’s work on recombination of characters showed that existing characters of individuals might produce a number of new combinations offering new variations for natural selection to act upon.
Many of the supporters of Darwin worked in various fields and tried to interpret Darwinism in terms of modern developments. The essential synthesis of all these theories along with the Darwinian theory of natural selection has come to be known as Neo Darwinism. The names of Huxley, Haldane, Goldschmidt, Dobzhansky, Fischer and others are important in the Neo Darwinian theory of evolution. The
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Neo Darwinism is also regarded as the modern synthetic theory of evolution. This theory combines the good aspects of mutation theory of de Vries, the natural selection theory of Darwin, the principles of inheritance of Mendle and the germplasam theory of Weismann. According to the Neo Darwinian theory of evolution there are five basic factors involved in the process of organic evolution. These are
1. Gene Mutations
2. Changes in chromosomes structure and number
3. Genetic recombination
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4. Natural selection and
5. Reproductive isolation
While the first three factors are responsible for providing genetic variability, the last two provide a direction to the evolutionary process. The Neo Darwinian theory states that “evolution is the product of genetic changes occurring under the influence of natural selection.” Another factor which is basically essential is the isolation of genetically changed forms.
Genetic changes are caused by gene mutations. Natural selection acts upon the new genotypes in the population and picks up the favoured ones and allows them to reproduce, when populations with useful genotypes are isolated for a long time they tend to originate into a distinct species from the one they belonged to originally.
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Thus isolation is one of the fundamental factors for evolution. Isolation which is brought about by migration may be geographical, climatic, genetic, reproductive or ecological. Isolation checks free inbreeding of organisms. This explains as to how new species originate when free inbreeding among the individuals or species is controlled by isolation.