Question

why is the variation beneficial for species not necessarily for an individual belonging to species

Answer 1

Variation is necessary for the survival of the species as variation makes species more adaptive to survive with the changing conditions. At the species level these variations can make difference at each generation but at individual level organism is not evolving but is ageing. if an individual naturally accumulates variation in his gene composition through mutation or any other source could be harmful. Thus variation at individual level  is not so useful as a person doesn't evolve by these variations.

Answer 2

♤ A species include large no. Of individuals of same kind. All the organisms of a species have similar body design and well adapted to the place.

♤ If there is a variation arise from the individual it might not be beneficial to it, even this variation may lead to the death of the individual.

♤ but the variation may be beneficial if the species faces a drastically altered condition.

♤ In this condition the population may wiped out completely but of some variation are there few individual can survive and thus variation is beneficial for the species.