Variation arise in an organism during reproduction that is during the DNA copying some error may occur by chance which gives rise to variations, and this is passed down to their offsprings.

Variations can be beneficial or detrimental that is variation is sometimes useful for the survival of the species; this is justified with the following examples:

i. If the temperature of the water increases suddenly, then most of the bacteria living in that water would die. Only a few variances that are resistant to heat would be able to survive. However, if this variance were not there, then the entire species of bacteria would have been destroyed. Thus, this variant help in the survival of species.

Hence if some variations are there, few individuals might survive. Depending on whether the variations are useful to the change in the environment some variants survive whereas others do not.