The GM Debate

The GM Debate

You already know how a gene is moved into a crop or a bacterium. This module is about whether we should, and about writing an answer that gets credit for saying so. Evaluate is a command word with a specific meaning. It does not mean "list the good things and then the bad things". It means weigh them: say which considerations carry more weight and why, and then commit to a conclusion. An answer that describes both sides and stops is an unfinished evaluation, and it is the commonest way to lose marks on this topic.

The two cases

Both columns contain real, documented effects. Neither is a list of things people merely feel:

Which case is which?

Fifteen years later

Bt maize kills the caterpillars that attack it, and for years it works. After about fifteen seasons of continuous planting, farmers in some regions report the caterpillars are back and the crop is being damaged again. Explain what has happened, using this topic's own ideas.

• Natural selection. A few caterpillars in the original population already carried an allele that let them survive the toxin. Everything else died, so those few did almost all the breeding, and the resistant proportion climbed every generation until it was the majority
• The caterpillars adapted to the toxin because they were exposed to it repeatedly
• The maize has gradually lost the inserted gene over successive generations
• The toxin caused mutations in the caterpillars that made them resistant to it

How the resistance spread

Put the stages of that process into order.

• Within the caterpillar population, a very small number already carry an allele giving some resistance to the toxin
• Bt maize is planted across the whole region, season after season
• Almost every caterpillar without the allele dies before it can breed
• The survivors breed with one another and pass the allele to their offspring
• The proportion carrying the allele rises with every generation
• After many seasons most of the population is resistant, and the crop is damaged again

What "evaluate" is worth

Four things separate an evaluation from a list. Weighing, not listing. Say which consideration you think matters more, and why. "There are benefits and there are risks" is a description of the question, not an answer to it. Specific examples. "GM can add nutrients" is a claim. "Golden rice makes beta-carotene, which the body converts to vitamin A, and deficiency is a leading cause of childhood blindness" is evidence. A conclusion with a reason attached. Not "so I think GM is good", but "so on balance the case is strongest where the alternative is crop failure, because the risk of doing nothing is also real". Conditions, if you can manage them. The strongest answers say when the answer would change: "for a crop with no wild relatives nearby, the gene-flow objection largely falls away." Naming what would change your mind is the clearest evidence that you weighed anything at all.

Which conclusion earns most?

Four students end an evaluation of GM crops. Which conclusion would score highest?

• "On balance I would approve it here, because the region already loses harvests to drought and that risk is certain, whereas the gene-flow risk is manageable when no wild relatives grow nearby. Were there wild relatives in the area, I would want buffer zones before approving."
• "In conclusion there are strong arguments on both sides, and it is a difficult issue that different people will view differently."
• "In conclusion GM crops should definitely be grown, because the benefits clearly outweigh the risks."
• "In conclusion, GM crops increase yields, add nutrients and make medicines, but they may affect biodiversity, have unknown health effects and are expensive for farmers."

The golden rice case

What it is. Ordinary rice makes beta-carotene in the leaves but not in the grain. Golden rice carries added genes so the grain makes it too, which is what gives it the colour. The body then converts beta-carotene into vitamin A; the rice does not contain vitamin A itself, and getting this the right way round matters, because the conversion is part of why the dose is argued about. Why it was attempted. Vitamin A deficiency is a leading cause of preventable childhood blindness and raises the death rate from ordinary infections. Rice is the staple food of the affected regions. What actually happened. The science worked in the 1990s. Approval and deployment took roughly two decades, held up by regulatory processes, sustained opposition, and a real argument about whether it treats a symptom of poverty and a narrow diet rather than the cause: a household that could afford vegetables and eggs would not need it. Why it is the best case to cite. It is not a simple story of good science defeated, nor of a corporate stunt. Both of the strongest arguments in this debate can be made from it, which is exactly what makes it useful in an evaluation.

For or against?

Each of these is a real, documented finding. Select the THREE that a critic of GM would cite.

• Herbicide-tolerant crops let a farmer spray one broad-spectrum herbicide over the whole field, and weeds in those fields have begun evolving tolerance to it
• A farmer who saves seed from a patented GM harvest to sow the following year may be in breach of the licence they agreed to
• Pollen from GM oilseed rape has been detected in plants several kilometres from the field where it was sown
• A GM salmon reaches market weight in about half the usual time, so less feed is consumed for each kilogram produced
• Insulin from engineered bacteria removed the need to extract it from the pancreases of slaughtered pigs and cattle
• Fields of Bt maize are sprayed with less insecticide, and surveys find more non-target insects in them than in conventionally sprayed fields

The words to use

Using the technical term rather than the everyday one is worth marks on its own:

How could each risk be reduced?

The approval panel

A country is deciding whether to approve a GM drought-tolerant wheat. You are advising the panel.

• The developer's trials show a 30% yield gain in drought years. A panel member says company data cannot be trusted. What is the proportionate response?
• Ecologists report wild wheat relatives growing within 2 km of the proposed fields. What follows?
• The panel must report. Which report is the strongest?

Write your evaluation

Evaluate whether GM crops should be grown. Name specific cases rather than making general claims, and follow the model from the callout: weigh, do not list.

• Give one benefit with a named example and a figure or a specific effect
• Give one risk with a named example, and say whether it can be managed
• Say which of the two you judge to weigh more heavily, and why
• Name a condition under which your answer would be different

Debate summary

Golden rice is engineered to make _____, which the human body then converts into vitamin A. Arguments against GM include the modified gene spreading to _____ relatives, which can be reduced by buffer zones but never reversed. Where a GM crop kills a pest, it applies a strong selection _____, so resistance can spread through the pest population by natural selection. A strong evaluation does not list both sides; it _____ them and reaches a justified conclusion.