Since a protein is specified by a DNA segment or gene, future copies of that protein can be modified by changing the gene's underlying DNA. One way to do this is to isolate the DNA, cut it, and splice in a different DNA segment. Daniel Nathans and Hamilton Smith received the 1978 Nobel Prize in physiology or medicine for their isolation of restriction endonucleases, which are able to cut DNA at specific sites. Together with ligase, which can join together fragments of DNA, restriction enzymes formed the initial basis of recombinant DNA technology.
Supporters of genetic engineering insist that any modifications are harmless and actually contribute to enhancing specific features of the crops. However others oppose this view, taking the stance that proponents are almost always in a position to gain from the technology. For example, American maize farmers and seed producers have benefitted financially from the development of varieties that are toxic to plant eating insects (see bt corn). However, the genes for this resistance have rapidly left the American fields, and are now present in multiple strains of wild and domestic maize. This amounts to a comtamination of the very gene pool from which the domestic maize was derived.
Anti-genetic engineering groups propose that genetic releases such as this represent the opening of a Pandora's Box which may ultimately accelerate the collapse of the modern non-sustainable system of agriculture, decreasing rather than increasing the food supply. They say that with current recombinant technology there is no way to ensure that genetically modified organisms remain under control, and the use of this technology outside of secure laboratory environments carries grave risks for the future.
However proponents cite the benefits that the technology can have, for example, in the harsh agricultural conditions of third world countries. They say that with modifications, existing crops would be able to thrive under the relatively hostile conditions providing much needed food to their people. While submitting that precautions should be made to ensure that any modified crops are contained, they say that their genetically engineered crops are not significantly different from those modified by nature, and by extension are not dangerous to other crops.