The human genome changes ever so slowly over the eons. What nourished our ancestors and what they tolerated has EVERYTHING to do with what nourishes us and what we tolerate. That is not to say that we do not tolerate food crops which man has developed over the centuries through selective breeding, which could occur in nature after all. In most instances, man of thousands of years ago might have tolerated many such crops quite well. Trans-gendered food crops and crops artifically mutated by man which were highly unlikely to evolve in nature are quite another matter. They are anything but natural and we do not tolerate them any more than we tolerate the vast majority of man-made pharmaeuticals and chemical compounds. Why? Because all of those are things that we have not lived alongside and adapted to for thousands of years. These are truths which should be obvious.