Some crops, such as soya, have had a gene added to them to increase their resistance to pesticides so that farmers can use pesticides more efficiently. But the fact that in some cases the same company that produces the modified soya seeds also produces the pesticide has led to allegations of corporate manipulation of food markets. And this is one of the chief fears about such foods. That they are a market-driven juggernaut oblivious to concerns wider than profit. Many believe that the genetic engineering lobby has been just a bit too complacent about safety.
Life is complex and has an unfailing capacity to surprise.
We have a lot to thank the Green revolution for but we must remember evolution's ability to frustrate human desires.