Darwinism is also known as Theory of Natural Selection. According to the Darwin, out of the vast number of individuals which compete for a place in the world, only those having advantageous variations survive and reproduce. This note provides us the information about Darwin's theory and mutation.
Charles Darwin, an English naturalist wrote a famous book named Origin of Species which was published in 1859 AD. Darwinism is also known as Theory of Natural Selection which can be explained in the following points:
Rapid rate of multiplication or enormous fertility: Every species tends to multiply in geometric ratio. It means that population doubling its number in one year increases four times next year.
Struggle for existence: Struggle helps to make the size of its own population constant. Organisms of different species compete with eachother for food and shelter. Here, only one species of organisms lives which struggles more. Struggle may be interspecific or intraspecific. It may be the struggle of individual of different species or of different species.
Variation and heredity: Even though the offspring are very similar to their parents, they are not identical. They differ from each other to some or more extent in size, shape, behavior etc. that is called variation.
Natural selection: According to the Darwin, out of the vast number of individuals which compete for a place in the world, only those having advantageous variations survive and reproduce. The nature choose only those individuals, which are fittest, only they survive and reproduce successfully.
Origin of natural species: Due to the changed useful characters, the individuals survive and may acquire more useful characters to survive in the struggle. About the evolution of giraffe, Darwinism suggested that the ancestral of giraffe were believed to have short neck or of different size. When there was shortage of grass, long neckedgiraffe were able to eat leaves or foliage but short necked were not able. Like this, because of competition and natural selection, only long- necked giraffe survived and short necked giraffe disappeared.
Criticism of Darwinism
Darwinism does not explain the origin of variation.
It is not always the case that useful variations are selected.
Natural selection is not the sole cause of specification but it is not only a guiding factor.
Darwinism does not always explain the presence of vestigial organs found in organism.
Mutation theory was given by a Dutch Biologist named Hugo De Vries, in 1901 AD. Mutation is defined as a sudden chromosomal change by which variation occurs in organism. Mutation occurs by the effects of radiation and chemicals called mutagens. An organism affected by mutation is called mutant. The majority of mutations are harmful, but a very small proportion of them may be useful for an organisms. Mutation is a main factor for evolution. Some of the examples of mutation are black patch on body, disability by birth, cut at lip, six- fingered limbs etc.
Things to remember
Darwinism is also known as Theory of Natural Selection.
According to the Darwin, out of the vast number of individuals which compete for a place in the world, only those having advantageous variations survive and reproduce.
Mutation is defined as a sudden chromosomal change by which variation occurs in organism.
It includes every relationship which established among the people.
There can be more than one community in a society. Community smaller than society.
It is a network of social relationships which cannot see or touched.
common interests and common objectives are not necessary for society.
The variation which occurs by gradual changes in hereditary character is called continuous variation, e.g. increase or decrease in the height of a man. The variation which occurs by sudden change is called discontinuous variation.
French biologist 'Jean Baptiste de Lamarck' is the founder of the theory 'use and disuse organs'.
The drawbacks of 'Darwin's theory of evolution are given below:
a) The natural selection is only a factor for the evolution of a new stage but not a complete factor because there is a variation in organisms evolved by mutation.
b) How variation occurred in human beings or other organisms is not described by Darwin's theory.
c) There would not be the selection of disused parts if there were only the selection of useful variation in the nature.
Since, successful and advantageous variation in characters inherited, the new organisms can survive longer in the changing environment. Sometimes special characters are seen offspring, which gradually modify from generation to generation. Ultimately, the organism looks quite different from its ancestor. If there were no such ancestral characters, perhaps there would be no evolution of new organisms. In this way, new organism has evolving from a common ancestor.
The mutation is defined as the sudden changes in the hereditary constitution of organisms. Example of mutation are disability of person by birth, cut at lip, six fingered limbs etc. An organism affected by mutation is called mutant.
The causes of mutation (like radiations and chemicals) are called mutagens.
Atavism is the sudden appearances of certain characteristics that are absent in present forms but were present in our ancestors; e.g. presence of long hairs on the body or face, or the presence of small tail by the birth of a person.