What impact do genetically modified organism have on the environment?

Question

What impact do genetically modified organism have on the environment?

Answer 1

Despite some highly sensational coverage of the issue in the press, there appears to be virtually no impact of GMOs on the environment so far.  The only case I can think of is the one involving monarch butterflies a few years ago.  The butterflies were ingesting pollen released by corn carrying a gene that makes an endogenous pesticide (the Bacillus thurengensis toxin).  Certainly a few butterflies undoubtedly died but the impact on the species was minimal.

It should be understood by all in the public that GMO crop plants currently under cultivation and any to be released in the future undergo highly rigorous testing to ensure safety.  There have been no proven adverse medical consequences to humans.  Likewise, no effects on the environment.