I don't think you understand evolution. Each organism doesn't evolve from scratch. Each organism builds upon the positive attributes of the previous. It may take thousands of years for a genetic "mishap" to show itself at as a positive attribute, but the mishap only took minutes. Humans happen to be the most evolved species right now, and therefore are at the top of the food chain. Artificially propping up species that don't have the means to survive in today's world isn't necessarily good for the planet.