The modification of crops is nothing new; plant breeders have been doing it since agriculture began. The wonderful range of apples or potatoes we now enjoy is the result of crossing different varieties. Cabbages, cauliflower and broccoli all originated from one botanical species. Modern molecular biology has given us the ability to go much further. We can now isolate the gene for a particular characteristic of an organism and transfer it to another species. It is this practice of transforming a plant with alien genes- perhaps from an animal or bacterium – that is causing all the controversy. There are three main concerns. Scientists can now take a gene for resistance to a particular herbicide and transfer it to crop: when these plants are sprayed with a weed killer, the weeds are destroyed while the crop is unharmed. One worry is the harmful effect this could have on the biodiversity of farmland, where so many insects, birds and other animals depend upon “weed” species. Another fear is that alien genes from a genetically modified (GM) pant could escape into a wild population of a related species. Since plants are fertilized by pollen which is carried through the air, often for great distances, this is entirely possible. A wild species modified in this way with pesticide resistance could become a “superweed”, while a species that becomes unnaturally resistant to animals that feed on it could disrupt the food chain. The third worry concerns a proposal to produce seeds for cereals that cannot germinate or produce next year’s seeds. This ‘terminator’ technology would be of obvious advantage to some companies since farms would be forced to buy new seeds annually. But it could be devastating to a farmer in the developing world who depends upon saving some seeds for next year’s crop.