This piece was originally published in 1998 by the Royal Agricultural Society of England in a booklet Old Crops in New Bottles? Six thoughts on the science of genetically modified crops. I stand by everything in it, although I’ve long since given up trying to change anyone’s attitude, unless asked.

Nothing new under the sun

Prince Charles certainly touched a nerve with his article in The Daily Telegraph. He rejects genetic modification because “we simply do not know the long-term consequences for human health and the wider environment.”1

The UK’s favourite science populariser, Richard Dawkins, wrote: “The ... thing you can say to Prince Charles is that, if you look at a maize cob, it is hugely different from a wild maize cob and that has been achieved not by introducing foreign genes but by artificially selecting genes. ... You could call a maize cob a Frankenstein plant, but every one is quite happy to eat maize cobs. There's a general feeling that [GM] foods are almost radioactive. The reaction has been as if people believe genetically modified plants are poisonous, or they give you cancer or they degrade your immune system. Well anything can do that.”2

In this paper I want to argue that GM crops may have provided a new focus for protest, but that the concerns expressed owe little to the specific processes of genetic manipulation. Worse, by focusing on questions of science and safety, both sides risk losing sight of the real issues. As a biologist and science writer I have watched the development of genetic engineering from the start.3 My central thesis here is that genetic modification is just the latest technology to serve the massive intensification of agriculture. There is nothing new about either the benefits it promises or the risks it threatens, many of which are already upon us.

Herbicides and insecticides

Farmers have been spraying herbicides and insecticides for decades, wiping out anything that, they think, competes with their harvest. Naively, one thinks that a bumper harvest makes for a happy farmer. In reality, the farmer does best out of scarcity, as the Porter in Macbeth knew full well:

“Knock, knock, knock! Who’s there, i’ the name of Beelzebub?
Here’s a farmer that hanged himself on the expectation of plenty”.

Plenty pushes prices down. Best, for the farmer, is to have plenty in a time of general scarcity. The farmer who can afford to protect a crop from pests will more than recoup his costs by selling into a short market; but that is true for all farmers. The result is an upward spiral in which all the farmers are using more pesticides and herbicides than they should be, biologically and economically. That undermines the value of the pesticides and means that the farmers often fail to recoup their costs. Worse, it squanders the value of the pesticide, by selecting for resistance. Prince Charles pointed the finger at genetic modification, but farmers did not need GM crops to create massive pesticide resistance in the past.

The darling of the genetic engineers is a bacterium called Bacillus thuringiensis, or Bt for short. Organic farmers like it too, because it is a natural product and thus is good. But several economically important pests have become resistant to Bt, not because they feasted on crops genetically modified to make Bt toxin but because farmers overused ordinary, old-fashioned spray-on Bt.

Warning signs appeared in 1986 on the island of Oahu in Hawaii; a watercress grower noticed that some diamondback moths in his field were not succumbing to Bt. Experts at the University of Hawaii decided that the numbers involved were insignificant and the farmer continued to spray. By 1989, three years later, the proportion of resistant moths had doubled. Moths resistant to Bt had turned up in another watercress field on Oahu and in a cabbage field on the big island of Hawaii. The trickle turned into a flood. Resistant moths appeared in Thailand, the Philippines, Japan, Florida and New York. In every case the growers were using frequent, high doses of Bt; one sprayed 15 times in a year.4

Diseases too have become resistant in exactly the same way. Most worrying, worldwide, is probably the resistance of late blight (Phytophthera infestans) to the fungicide metalaxyl. Since 1992 blight strains resistant to metalaxyl have spread around the world, and the disease is expected to reduce global potato output by 15 per cent. In a sense it is a miracle that it has taken so long for resistance to metalaxyl to emerge, as potatoes consume more fungicide than any other foodstuff and in some places are routinely sprayed every two weeks.

Genetic pollution

Prince Charles notes that pollen from a GM oilseed rape has turned up in conventional crops more than a mile away. Pollen from rape has always travelled this far, and ironically it is only the tools of genetic engineering that allow scientists easily to monitor the flow of pollen. But unless the conventional crop is being raised to produce fresh seed, in which case contamination is something the farmer ought to be on guard against no matter what its source, the fact that the pollen is from a genetically modified plant presents no additional hazards.

While protesters worry about a Gene Smog, drivers along Britain's roads can already marvel at conventional genetic pollution. Smears of the brilliant yellow flowers of oilseed rape (Brassica napus) are a familiar sight wherever grain lorries have spilt their seed, with no help from GM varieties. That and the spread of agriculturally-improved varieties of wildflowers5 are clear evidence of genetic pollution that owes nothing to genetic engineering.


Pollen transfer prompts another of the big fears, superweeds resistant to all the pesticides one can throw at them. Again, conventional agriculture has already managed this rather well.

In Manitoba on the Canadian prairies, two-thirds of the crop land has patches of wild oats resistant to two or more classes of herbicide. In 1997 triple and quadruple resistant oats appeared. Weed scientists with Agriculture Canada blamed farmers who ignored advice to rotate crops and herbicides.6

In 1996 an annual ryegrass resistant to glyphosate appeared in Australia.7 It was the first resistant plant species in 20 years of glyphosate use. No Roundup Ready crops were involved, and some Australian populations of annual ryegrass can now survive all the herbicides registered for their use.

Goose grass has become resistant to dinitroaniline herbicides such as trifuralin and oryzalin. Scientists finally understand at a detailed molecular level exactly why they are resistant (proved, incidentally, by manipulating the mutant gene into maize to make it resistant too) but as the researchers point out, in the wild this resistance “has arisen, and been selected for, as a result of repeated exposure to this class of herbicide.”8

Unsafe food

The final spectre is that eating GM foods can be dangerous. Again, GM foods pose no new threats.

The intensification of the food supply industry has contributed to the safety (or otherwise) of ingredients and food in many ways. A simple example: feeding cattle grain considerably increases the number of Escherichia coli bacteria in their gut, and those bacteria are more resistant to acid. Because they are more numerous, the E.coli from grain-fed cattle are, all else being equal, more likely to make their way into the human digestive system and, being better able to resist acid attack, they are more likely to survive their trip through the stomach. If they are of the virulent strain 0157 the result can be fatal. Cattle are fed grain because it is cheaper and more fattening than hay, but farmers do not have to abandon grain feed and consumers do not have to stomach the increase in meat prices that would accompany a switch back to grass. Feeding cattle on hay (or silage) for five days before slaughter greatly diminishes the number of acid-resistant E.coli in the gut.9

It is also worth bearing in mind that the human diet contains a huge number of entirely natural, unselected items that are extremely unsafe if not properly prepared: fugu and cassava are two obvious examples, but there are hundreds of others.10 GM crops can pose a risk. For example, people with nut allergies may react very badly to a food or ingredient that contains genes from nuts. But they have always run the risk of unwanted pieces of nut finding their way into, say, chocolate bars. The issue is one of information about the food, not the process that created the ingredients.

The response

GM crops pose no potential threats that intensive agriculture has not already made a reality. But because opponents have focused on “scientific” worries, the biotech industry has been able to respond by trying to show that those fears are groundless, an emphasis -- on both sides -- that has been pretty unedifying.

Most damaging, probably, was the claim in a recent TV documentary that GM potatoes weaken the immune system of rats. World in Action showed the work of Dr Arpad Pusztai, at the Rowett Research Institute in Aberdeen, on potatoes engineered to express lectins, general-purpose anti-feedants that are found in many plants and that gum up the digestive system of any insect that eats them. The rats fed the GM potatoes suffered stunted growth and weaker immune systems. Opponents of GM foods were jubilant.

But the rats with the weakened immune systems, which Dr Pusztai discussed, had not been fed GM potatoes, they had been fed ordinary potato with added lectin, a so-called positive control. And the results were exactly what they should have been. It would have been very odd indeed if lectins had not been harmful. No-one else knows why Dr Pusztai made the claims he did, but the director of the Rowett suspended him from all studies of this nature and told him to retire. Headlines that screamed “Genetic Foods May Harm Humans” were soon followed by “Food Scientist Got It Wrong”. The details of the story are complex11 and doubtless we have not heard the last of it. Protestors (and not a few politicians) quickly said that the (erroneous) results strengthened the case for an end to GM crops, but industry was able to point to the fact that existing regulation would not have allowed such crops onto the market.

Superweeds throw up similar difficulties. Scientists from Ohio State University and Risoe in Denmark collaborated to study the movement of herbicide resistance genes from oilseed rape to its weedy wild turnip relative B. rapa. They found that the turnip picked up the resistance gene easily, and survived just as well as those that were not resistant, even in the absence of herbicide.12

But scientists at the University of Reading, who also studied the movement of genes from cultivated B. napus to wild B. rapa, came to a different conclusion.13 Fewer than 1 in 14 populations showed any hybrid seeds at all. Where there are hybrids, they form between 0.4 and 1.5 per cent of the seeds. And of the hybrids, less than 2 per cent survive as seedlings. The scientists conclude that the potential for “transgene recruitment [into the wild population] is likely to be slow and uncertain”.

Science is just not capable of providing a single, simple answer. And as long as there is some uncertainty the biotech industry, like the tobacco industry before it, will be able to keep operating.

The question of resistance has been tackled by government and industry drawing up management plans and hoping they will do the trick. Take Bt. In 1996, Bt corn accounted for less than one per cent of all US production; by 1998 it had risen to 19 per cent, 4.2 million acres. The risks are greater than with a spray, because Bt is present all through the season, in all the plants, instead of temporarily and patchily. Novartis Seeds Inc, one of the industry leaders with its Bt corn, offered a financial incentive to help farmers make the tough decision to forego some pest resistance. Novartis proffers growers “substantial savings if at least 20 per cent of their order includes non-Bt hybrids.”14 The idea is that farmers will create refuges of non-Bt corn, where susceptible pests can survive and thrive, mating with occasional resistant specimens. (But only if they buy all their seed from Novartis ... )

The irony is that having seen the value of Bt corn, farmers are unwilling to sacrifice a single ear. The National Corn Growers Association noted that “if the refuge requirements are too onerous, growers will not be able to justify using the technology from an economic perspective”. In case that's too abstruse, NCGA board member Tim Hume spelled it out: “Bt corn has shown us just how much yield we are losing to corn borers, and we are not willing to accept that yield loss anymore. ... Raising the refuge requirement moves growers away from Bt and back to sprays, and I don’t think that’s what anyone envisioned when we first heard about the promise of this new, environmentally compatible technology.”15

One Canadian farmer said that the refuge strategy would fail because no farmer will pay a premium price for Bt hybrids if he has to plant “junk” hybrids on 25 per cent of his acreage. Most progressive farmers, he said, would buy and plant the new hybrids edge-to-edge and leave it to their less-progressive neighbours to stick with the cheaper, older varieties without the Bt gene. If that farmer is correct, said a Canadian agricultural journalist, “it’s a sad situation. It speaks of farmers being totally selfish, of farmers defying logic.”16

Sadly, experience suggests that the farmer is correct, as the use of Admire to control Colorado beetle in potatoes shows. Farmers were warned to use Admire sparingly to avoid the spread of resistance, which the beetle has developed to every other insecticide deployed against it. But many North American farmers ignored that advice and rely totally on Admire. And the beetle is resistant.


Basing an argument on the desire for scientific certainty, especially in a culture that understands neither statistics nor risk and that has not embraced the precautionary principle, always permits one’s opponents to come up with countervailing conclusions. My suspicion is that opposition to GM crops is actually a lot more emotional than most people will admit. “I believe that this kind of genetic modification takes mankind into realms that belong to God, and to God alone,” wrote a very honest Prince Charles. He was referring specifically to transferring genes between distantly related species, like the mythical strawberry-with-fish-anti-freeze that upsets some people inordinately. Again, a hostage to fortune. What if the gene sequence came from a flounder, but the physical gene was manufactured at the laboratory bench? This is not such a far-fetched idea: the first mammal gene engineered into a bacterium was an entirely synthetic version of the human anti-growth hormone gene, and that was almost 20 years ago.17 What if the anti-freeze came not from a fish but from a carrot?18

Objecting to the source of the gene is thus fraught with difficulties. Objecting on principle is equally hard. Prince Charles made an exception for “certain highly beneficial and specific medical applications,” so we can assume he would be in favour of plants engineered to make vaccines. These already exist for foot and mouth disease in cattle, diarrhoea in humans, and against the bacteria that cause tooth decay; more are in the pipeline. Are those GM crops acceptable? Are crops engineered to provide feedstocks for a chemicals industry that currently uses petroleum?

Opposition to GM crops and foods is loud. In the UK, the government seems now to favour a three-year temporary moratorium on the commercial growing of GM crops, though the use of GM foods produced elsewhere seems not to be under any regulatory threat. The response of farmers in this country will be interesting. Global problems -- especially of resistance -- are the result of individual local actions. Farmers to date have shown no evidence of having the greater good at heart. And why should they, when, like other industries, they tend to reap the profits themselves while society at large pays the costs.19

Opponents of GM crops should come out with it and admit that they just don’t like it, even though that might require some painful case-by-case decisions. Farmers would do well to stand back and ask whether they cannot reap the benefits offered by GM crops by using other techniques, with the added gain of producing a product people might actively prefer, for whatever dubious reasons.

Jeremy Cherfas is a biologist who has followed the unfolding story of genetic manipulation since its birth in the 1970s. He writes and broadcasts on matters of food and agriculture.


  1. Seeds of disaster, Prince Charles, 10 June 1998, Daily Telegraph. 

  2. Richard Dawkins, August 14, 1988 The Independent. 

  3. Jeremy Cherfas (1982) Man Made Life: an overview of the science, technology and commerce of genetic engineering, Blackwell Scientific Publishers: Oxford. 

  4. Tabashnik, B.E. (1994) Ann. Rev. Entomol. 39: 47−79. Tabashnik, B.E. (1997) Proc. Natl. Acad. Sci. USA 94: 3488−90. 

  5. Akeroyd, John (1994) Seeds of Destruction? Non-native wildflower seed and British floral biodiversity. Plantlife: London. 

  6. Super wild oats gains herbicide resistance, D'Arce McMillan, August 13, 1998 Western Producer. 

  7. Supergrass sets alarm bells ringing, New Scientist, 6 July 1996, p 6. 

  8. R. G. Anthony et al (1998) Herbicide resistance caused by spontaneous mutation of the cytoskeletal protein tubulin, Nature 393: 260. 

  9. F. Diaz-Gonzalez, T. R.Callaway, M. G. Kizoulis, and J. B. Russell (1998) Grain Feeding and the Dissemination of Acid-Resistant Escherichia coli from Cattle, Science, 281:1666−8. 

  10. D.E. Carr (1972) The Deadly Feast of Life, Heinemann: London. 

  11. Poisonous potatoes: a case study in miscommunicating science, 13 August 1998 issue of The Bowditch Group Electronic AgBiotech Newsletter ( 

  12. Allison A. Snow, Bente Andersen, and Rikke Bagger Jørgensen (1988) Costs of transgenic herbicide resistance introgressed from Brassica napus into weedy Brassica rapa, Molecular Evolution (in press). 

  13. Scott, S.E. and Wilkinson M.J. (1998), Nature 393: 320. 

  14. Novartis Seeds Inc., Press Release, 21 September 1998. 

  15. National Corn Growers Association, Press Release, 24 September 1998. 

  16. Bt corn and refugia, Jim Romahn, 8 October 1998 Manitoba Cooperator. 

  17. See Cherfas, op.cit. p 145. 

  18. L. Worrall et al. (1998) A Carrot Leucine-Rich-Repeat Protein That Inhibits Ice Recrystallization, Science 282:115-7. 

  19. Garrett Hardin (1993) Living Within Limits, Oxford University Press: Oxford. 

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