GM occurs in nature all the time. Retroviruses inject their genetica material into the host genome and sometimes it stays there. Becoming part of the genome that is passed on to future generations.
The bacterim A.tumifaciens naturally does what geneticists are making do in the lab. Throughtout its existence it may have been responsible for millions of Genetic Modifications that we are not even aware of. Scientists are doing and expanding on this naturally occuring process
We should also note the difference between TRANSgenic and CISgenic.
A Cisgenic tomato for example would contain the genes from another tomato variant. The genes come from the plants own gene pool, and could naturally cross.