According to the World Health Organization (WHO), there is a very real risk of out-crossing, which refers to the transfer of engineered genes (transgenes) from genetically modified crops to conventional, cultivated plants or to related crop species in the wild. This may happen by means of wind, insect pollination, or other transfer.
The foreign genes can cross with and contaminate these other species, resulting in a hybridization of the genetically modified crop plant with a non-GMO plant. This could radically alter entire ecosystems if the hybrid plants thrived.
Out-crossing can also have an indirect effect on food safety and security, as the contaminated species make their way into the food chain. In a September 2010 paper, for example, the World Health Organization reports an incident in which traces of a GM variety of corn that was only approved for use as livestock feed was found in corn products intended for human consumption in the U.S. market.
Learn more: http://www.naturalnews.com/029869_GMOs_dangers.html#ixzz4MfyVJvud