Genetic pollution occurs when domesticated or genetically engineered species interbreed with their wild cousins, thus polluting the wild species gene pool. Genetic pollution is seen as negative because it affects the wild population's evolved capability to survive, as well as spreading genes that are not found in nature.
One of the main issues with genetic pollution lies in the fact that man has tampered with the genetic structure of these species and has created a situation that would not be found naturally. Some people find no issue with genetic pollution however, stating that it is the natural course of events. One thing is certain, genetic pollution irrevocably alters a species, for better or worse.