Gene flow in the environment – genetic pollution?

Biological invasions have had profound effects on human society from the earliest times. The spread of the black death in the Middle Ages, the devastations of potato blight, the effects on indigenous species by grey squirrels, dutch elm disease and flatworms have all been seen as detrimental to man or the environment. Others are seen as bringing benefits: most of our crops evolved elsewhere in the world and many culinary and medicinal herbs were brought to Britain by the Romans. Perhaps the greatest invasion is the import of vast numbers of exotic plants to gardens and greenhouses. Ecological invasions are an intrinsic part of ecology and evolution and we only consider them bad if they impoverish our health, livelihood or living conditions.