What Are Genetically Modified Crops? Three Traits Doing Almost All the Work

Commercial genetically modified crops are dominated by four species, soybean, maize, cotton and oilseed rape, and by two trait categories:

• •Herbicide tolerance, which allows a field to be sprayed with a broad-spectrum herbicide that kills weeds and not the crop, simplifying weed control considerably
• •Insect resistance, in which the plant produces a protein from the soil bacterium Bacillus thuringiensis that is toxic to specific insect larvae and harmless to mammals, and which is the same substance organic growers spray
• •Stacked varieties combining both, which now account for a large share of plantings
• •A small number of other traits including virus resistance, which rescued the Hawaiian papaya industry from a devastating virus, and delayed ripening
• •Nutritional modification, of which golden rice engineered to produce beta-carotene is the best known and has taken decades to approach deployment
• •Drought tolerance and disease resistance in several crops, which are more recent and less widespread than the debate assumes

Two methods dominate the older generation. Agrobacterium-mediated transformation uses a soil bacterium that naturally inserts DNA into plant genomes, which was co-opted by replacing its own genes with the desired sequence. Biolistics fires microscopic particles coated with DNA into plant tissue. Either way, the insertion point is not controlled, so many transformed plants are produced and screened for those with a single well-placed insertion and the intended behaviour. Genome editing, principally using CRISPR systems, works differently and is the reason the regulatory categories are becoming strained: it can make a small precise change, including deleting or altering an existing gene, without inserting any foreign DNA at all, producing a plant indistinguishable from one that could have arisen through mutation. Several jurisdictions have therefore drawn a regulatory line between inserting foreign genes and editing existing ones, while the European Union's courts ruled in 2018 that edited organisms fall under the existing genetic modification rules, a position now under legislative review.

The scientific position on the safety of approved genetically modified foods is unusually consistent. Major reviews, including a comprehensive 2016 report by the American National Academies examining two decades of data, found no substantiated evidence of health harm from consuming them, and comparable conclusions have been reached by the European Commission research programmes, the United Nations health agency and national academies across many countries. The remaining scientific disagreement concerns environmental and agronomic effects rather than food safety. The most consequential of those is resistance: heavy reliance on one herbicide has selected for herbicide-resistant weeds across large areas, which is exactly what the same over-reliance did with earlier chemistry and is an agronomic management failure rather than a property of the technology, and insect resistance to the bacterial toxin has emerged where refuge requirements were not observed. Gene flow to wild relatives has been documented in some crops and is a genuine consideration where such relatives grow nearby.

Much of the opposition is not really about molecular biology, which is why presenting more safety data has changed few minds. Concerns about corporate control of seed are substantial and separate from the technology: patents on varieties, prohibitions on saving seed and consolidation among a small number of companies affect farmers regardless of how a trait was produced, and conventionally bred varieties are also protected. Concerns about intensive monoculture agriculture apply to the system the crops are deployed in. Concerns about regulatory capture and about who decides what risks are acceptable are political. And there is a legitimate argument about the opportunity cost of the regulatory burden itself, which is heavy enough that only large firms can meet it, which entrenches the corporate concentration critics object to and has kept publicly funded projects including golden rice in development for decades. The conflation of these distinct arguments under one label is the reason the debate has been so unproductive for so long.

Commercial genetically modified crops are mostly four species carrying two traits, herbicide tolerance and a bacterial protein toxic to specific insect larvae, frequently stacked together. Older methods insert foreign DNA at uncontrolled locations while genome editing can alter existing genes without inserting anything, which is straining regulatory categories. Major reviews find no substantiated health harm, and the real problems are herbicide-resistant weeds, corporate seed control and a regulatory burden only large firms can carry.