According to a report by United Nations Environmental Programme (Unep), human mobility has fundamentally altered the make-up and the character of the biological world, as more and more species, relocated from their natural home environments have as aliens been introduced, either intentionally or unintentionally, into the homelands of other species.
This co-mingling of species, the report says, has been on the increase ever since the age of exploration, and has accelerated dramatically in recent times, with the advent of mass transportation, travel, and trade.