Answer
Natural selection edits rather than creates because it filters out weaker or unhealthier genes.
Work Step by Step
Just as an editor chooses the best writing and removes errors, natural selection also removes errors and mutations by selecting out deleterious genes. Editors create a better piece of writing for the next draft or "generation" just as natural selection produces different genetic "drafts" in each generation. Just as an ethical editor would never add content to someone else’s writing, natural selection can also only select from variations present in the population. It does not create genes or variations; mutations arise through a different process.
