Explain how the concept of the "survival of the fittest" relates to the theory of evolution.

The fittest species for a certain biome will adapt and change so as to keep living. This process is evolution and an example can be giraffes. If they had smaller necks, they couldn't reach the tree tops where food is, so only the fittest one with large necks survived, and they evolved by having the entire species grow up with large necks.