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Despite the speed with which the subject develops, this week's report on the safety of genetically modified food, from a group chaired by Sir David King, the government's chief scientific adviser, will stand for some time as the definitive document on the consequences of GM. One question - Is GM food safe? - has been answered, and the answer is yes. But it would be naive to expect his report to make GM acceptable. The main scientific issue is the health of the environment, not the consumers of GMfood. Examples such as pesticide resistance show that there is no practical way of predicting the direction genes will take once in the wild.

It would be prudent to assume that any characteristic genetically engineered into crops or farm animals will emerge at some point in other species, perhaps our own.

Sir David's findings should be seen in the context of this month's Downing Street Strategy Unit document, which shows that public acceptance is the key to the future of GM. The food industry is keener on increasing the quality and price of the goods it sells than on new sources of bulk produce, so the outlook is dim. Nor are the economic advantages in the wider world apparent. No technology can solve the problem of people being unable to buy food. The solutions have to be economic, social and political, not scientific. Scientists should have the humility to admit that their expertise runs out at this point.

It may prove impossible to build support for GM among consumers. Resolving the impasse will call for better public dialogue in which science is only part of the picture. After all, the scientists who originally developed GM were sure that environmentalists would love it because it would cut pesticide use. Asking first would have revealed that the picture was a little more complex.