According to the European Union, food classified as GM contains genetic material that has been altered in a way that does not occur naturally by mating or recombination.
Their premise is that it is not natural to take genes from one organism and implant them in another. What are we talking about when we say 'genes'? Heuristically speaking, genes consist of a specific sequence of DNA base sequences (guanine,cytosine,adenine,and thymine) that lead to the expression of traits.
With traditional plant breeding, we develop plants with superior arrangements of DNA base sequences via the transfer of thousands of genes from one plant to another. These arrangements represent drastic changes in plant characteristics that would not have occurred naturally. (for example, modern corn scantly resembles its ancestor teosinte) Since the 1960's scientists have also been engaged in what is referred to as mutation breeding. In this procedure plant cells are attacked with gamma rays inducing ‘unnatural’ new combinations of DNA base sequences. Much of the pasta consumed in the world today is derived from wheat developed via mutation breeding. These changes to plant DNA are much more extreme than what molecular biologists are doing in the laboratory today.
Unlike traditional plant breeding methods, the laboratory techniques of molecular biology that are used to create ‘transgenic’ or GM plants induce very specific and precise changes in plants. The rearrangement of DNA base sequences is known and controllable. While these combinations would not have occurred naturally, the base sequences are common to all organisms and are as natural as can be. One could argue that the risk associated with these modern techniques is much less than with traditional crop improvement methods.