Wherever GM crops have been grown, some genes 'flow' into other non-GM crops or wild relatives. Until recently, some people claimed that this gene flow was of little importance because pollen didn't travel far - no more than a few hundred metres at most. But pollen from genetically modified maize may have travelled on the wind to remote parts of Mexico. GM maize, ordinary maize and wild maize (corn) are the same species so they can interbreed. Scientists from the University of California found that the stray pollen had crossed with wild maize. It may have come from GM maize trials in 1998. But those trials were 100 kilometres away. (There haven't been any trials since because Mexico has banned GM maize.) The worry is that long-distance drift of GM pollen threatens the purity of ancient crop varieties even if they grow in remote places [1]. Some contamination may have come from food aid imports of GM maize from the US. Mexican farmers may have planted some of this corn. These are other ways in which gene flow - unwanted contamination - can happen. There are several real worries about this[2]:

1. Mexico is the source of all original maize varieties from which all modern types have been bred - or genetically altered.
2. If this contamination has happened in Mexico so easily, it's only a matter of time before many more countries are also affected, partly because of GM food exports from the US or because of food aid shipments to starving people.
3. Organic farmers, wherever they may be, have to comply with strict regulations if they want to claim that the food they grow is truly organic. They are trusted by the growing number of people who buy organic because they want uncontaminated food. Among other things, the regulations don't allow farmers to use GM seeds or plants. So what happens when an organic farmer's crops are contaminated by genetically engineered crops growing nearby - as will happen more and more in the future? It means that people who choose to have uncontaminated produce simply won't be able to have that choice any more. Everyone everywhere will have to eat some form of GM food.
4. The GM varieties are owned. They are the patented 'intellectual property' of powerful companies. If farmers grow the companies' seeds without paying for a licence, the companies will take them to court and sue them for damages. This has already happened to a Canadian farmer, Percy Schmeiser, who claimed that his canola (rapeseed) was contaminated by RoundupReady canola seed from neighbour's fields or had blown from passing trucks. He had been saving the seed from his canola plants and sowing it for many years - as farmers have always done. Monsanto, the company that owns the patents on RoundupReady canola seeds, discovered Schmeiser's seeds included some of their patented weedkiller-resisting version. They took out and won a lawsuit against Schmeiser, claiming $400,000 in damages. What will happen if farmers in poor countries sow GM seeds or GM-contaminated seeds that they've saved? Will the companies sue them too?
   

1. New Scientist, 01/12/2001, 25.
2. ETC Group 'Fear-reviewed science', Jan-Feb 2002, Issue 74.