- The differences that are found between the individuals of same species are called variation.
- It is very difficult to find out two individuals exactly similar in the nature.
- It may be harmful, useless and useful.
- Harmful or useless variations make individuals unfit for struggle for existence, whereas the useful variations are quite significant and make organisms fit in the nature.
- Such variations are transmitted to the next generation so that the progenies are more suited.
Types of variations
Variations can be divided into various types. Some of the types are as follows:
A) Types of variations on the types of cells
i) Somatic variations:
- The variations that affect only the somatic cells are called somatic variations.
- These are not inherited from parents to the off-springs.
- These variations are acquired by the organisms during their life time and are lost with death.
- Such variations are also called acquired variation. These variations are not important for the evolution point of view.
- The possible causes of such variations are:
a) Environmental factors
- The environmental conditions directly influence the form and functioning of animals, plants and micro-organisms.
- The various abiotic and biotic factors introduce changes, some of which proved to be adaptive in nature.
b) Use and disuse of organs
- According to Lamarck, continuous use 0f an organ makes it better develop, whereas continuous disuse causes reduction in size.
- Examples: a player who uses his muscles acquires better and developed muscles, a blacksmith who uses his right hand has better and stronger muscles in the right arm than those of the left arm.
c) Conscious efforts
- Education, learning, training, nutrition and habit formation are examples of somatic variations due to conscious efforts.
- Small feet in Chinese and slender waist in European women are acquired by putting on tight shoes or tight clothes respectively.
- Mutilations, castration, different hairstyles, beard and moustache, etc. are somatic variations caused by human beings by conscious efforts.
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ii) Germinal variations
- The variations that affect the germinal or reproductive cells only are called germinal variations.
- These are inherited from parents to their off-springs.
- Hence, these variations are very important for the evolution.
- The possible cause of such variations are mainly due to recombination and mutations.
- Recombination occurs due to reshuffling of parental genes which results in organisms with new genetic combination.
- Due to the mutation, structural changes in DNA or chromosomes occur resulting into change in phenotype.
B) Based on degree of differences produced
i) Continuous variations
- These are small and indistinct variations.
- These fluctuate on the either side on the average condition.
- These are also described as the fluctuating variations or plus-minus variations.
- Since they are unstable and non-heritable, they do not have any role in evolution.
- These affect the size, weight, shape, or color of an organism or its part.
ii) Discontinuous variations
- These are large and sudden which deviate to a great extent from the normal and appear as totally new.
- These are also described as mutations.
- Since they are stable and heritable, they play important role in origin and evolution of species.
Significance of variations
- Variations form the basis of heredity.
- They constitute the raw material for evolution.
- They help in adaptation of organisms to the changed environment.
- Due to variations, useful variants of animals and plants are created.
- These provide each organism a distinct individual.
- These make individuals better suited for their survival in nature.
Variations and its types