It's a question of timing and targets, not quantity. This is one reason my question about farming background is relevant, from what you've been saying you clea

It's a question of timing and targets, not quantity. This is one reason my question about farming background is relevant, from what you've been saying you clearly don't have this background, let alone have ever used (generic) Roundup yourself. I've helped my father do so, in general weed killing applications, and he knows farmers who use the stuff for real, and just asked one, who said: You never let Roundup touch the plants you're growing---it only works when a plant is growing, BTW, in a "plantostatic" way, like bacteriostatic, it inhibits the synthesis of some critical amino acids. If you don't have Roundup Ready seeds, you spray before planting or after harvest, or you make sure the spray hits weeds, not your plants. That's because it's such a general killer of plants (assuming it can get inside, but that has no bearing on this discussion of genetics). And why it's so safe, animals cannot synthesize these amino acids (well, not without using one of the others as a precursor): https://en.wikipedia.org/wiki/Aromatic_amino_acids https://en.wikipedia.org/wiki/Aromatic_amino_acids So, no selection pressure on the crops themselves, unless you really screw up.