Question

varation is important for natural selection because ....

Answer 1

If there is zero variation, how could there ever be any selection? If you have two bags of marbles, bag A and bag B, and bag A has 75 white and 25 black marbles and bag B has 100 black marbles.

If there is selection for white marbles, such that if you drew a white marble in bag A you would remove a black marble in bag A and replace it with a white and put the original white marble back in, but if you pulled a black marble from bag A you would simply put that marble back in bag A; how could this selection ever act on bag B? There are no white marbles and thus the selection does not matter.

Answer 2

If you have different traits in a group, one (animal) of the group is most likely to survive in an extreme condition of change. this is called natural selection. if you have a variety of traits, one of the traits is bound to be suitable to whatever change comes.
hope this helps! :D