Why is variation beneficial to the species but not necessarily for the individual?

Variation is not necessary for an individual but it is very important for survival of a species. A population of reproducing organisms or a species are suited to a particular niche. If there is no variation among individuals of a species they can be easily wiped out in case of drastic change in niche. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Therefore, variations prevent the complete wiping out of species in adverse climatic changes in their niche.