Why is variation beneficial to the species but not necessarily for the individual?
Answers
At the individual level, variation is either great, sucks, or doesn’t really matter. Being the poor sod who rolled all ones and got all the sticky options is obviously not very beneficial. The fact that it could have been better doesn’t matter much to you. However, at the species level, there are hundreds, thousands, millions or more individuals, each with their own unique combination of quirks, traits and mutations. Those with good or benign mutations will thrive and help the species survive. Good changes obviously help immediately, and benign ones may one day become useful i.e. previously benign mutation actually provides resistance to a new disease. Those with sticky ones will likely die (or just fail to reproduce). Since there are so many others who didn’t suffer that fate, they can effectively be swept under the rug. From an evolutionary perspective, they might as well have not existed.
So at the individual level, variance doesn’t really matter. Either you got lucky or you didn’t. But at the population level, so long as most mutations are benign or better for passing on offspring the species will likely thrive, as the variation allows them to adapt to change.
Variations can be beneficial or harmful according to the ecological niche of the organism. A variation suitable for the particular niche is selected by nature in evolution. Thus variations are necessary for the survival of the species. Variation is important for evolution of the species.
E.g.: A population of heat resistant bacteria in temperature of the water survives, if the temperature of water increases by global warming but most other bacteria would die.