Variations

Variations can be defined as the differences that occur in the characteristics between members of the same species. Variations occur with reference to every character. In the absence of variations, every species would have continued to exist in the same form and no new species would have arisen from the existing one. Thus, variations are the raw materials for organic evolution.Types of Variations

Variations can be classified into the following types:
Somatogenic Variations

These are variations that are restricted to the somatic cells of the organism. Such variations appear anytime during the life of an organism and such variations die along with the organism. Hence, these variations are non-heritable.
Blastogenic Variations

These are variations that are found in the gene pool of an organism. They may be already present in the ancestors or may occur any time. These variations are heritable and form the raw materials for evolution.
Continuous Variations

These are graded variations that are always found amongst the members of a species with reference to certain characters. Individuals exhibit continuous variations with reference to characteristics like colour, shape, size and body configurations. Such variations have an adaptive value but they cannot bring about formation of a new species.
Discontinuous Variations

These are distinct variations that are caused by genetic changes brought about by environmental changes.
Sources of Variations

Variations are caused due to several factors listed below.
Mutations

Mutations are sudden heritable changes brought about by the composition of a gene or a chromosome. Accordingly, it can be a gene mutation or a chromosomal mutation. Sometimes, there may be just a change in the chromosome number causing a variation. It is called as ploidy or genomatic mutation. All such mutations bring about change in the genetic information of the cell and in turn the traits of the organism.
Recombination

These are genetic variations brought about due to shuffling of parental genes into new combinations. Thus, the resulting offspring exhibits genotypic variations. Genetic recombinations occur due to:

• Independent assortment of chromosomes during meiosis

• Reciprocal recombination of genes due to crossing over and

• Randomness in the fusion of gametes during fertilization

Genetic Drift

It is the change brought about in the gene frequency of a population by various factors. It may be involved in the elimination of genes pertaining to certain characters.
Natural Selection

It is primarily a process of differential reproduction. Some members of a population may have genes, which enable them to grow up and reproduce at a higher rate. This results in the formation of offspring having better chances of survival. Those organisms that produce large number of viable offsprings contribute to a greater percentage of genes to the gene pool of the next generation. If differential reproduction of this kind occurs for several generations, genes of the individuals, which produce more offspring, becomes predominant in the gene pool of that population leading to a change in the gene frequency.
Migration

Sometimes it is possible that members of two different demes of a species, which were separated from each other, come together due to migration of individuals. In such a situation the genes that are unique to each population (deme) intermingle due to inbreeding resulting in variations in the offspring.
Hybridisation

Variation could arise through a process of hybridisation, sometimes even in interspecific hybrids.
Genetic variability is necessary for a species to increase its chances of survival. The environment is constantly undergoing changes due to geological and biological processes. Hence, it is necessary for organisms to develop variations. The occurrence of variations in a population ensures that at least a few individuals in a population are able to adapt and survive in the changing environment.