It happens with stories, people make up a story but each time it is told it gets changed. It might be changed because people forget parts, or they think a different version is better. The story evolves to become what people want to hear.
It's important to note that it is not just the story that affects how good it will be but the environment around it: the people who hear it and the people who pass it on. People like different things.
It also happens with life; In fact we have evolved a fantastic method for evolving. This method is called genetic evolution. We are coded, like blue-prints, into a chemical called DNA. This allows us to replicate in an imperfect way (organisms are rarely exact clones). Mostly these changes do nothing, sometimes they are problematic, very occasionally they are beneficial. Anything that gets a benefit will be able to reproduce (copy) more times, meaning they will cover a higher percent of the population.
Sexual reproduction is another improvement in evolution. It's as if we combined two good stories or two good car blue-prints to make another.
As we continue to rush through the landscape of evolution history on earth we can see that certain events that seem to be detrimental can be beneficial. Fluke events can shape an entire lineage. Things don't have a plan. We are not forced to follow our genes.