Science in Society Archive

The Precautionary Principle and Scientific Evidence

Peter Saunders and Dr. Mae-Wan Ho argue: The precautionary principle is not an algorithm for making decisions, but a principle for making decisions based on available evidence. So let's look at the evidence.

In a recent article, Comstock claims that the precautionary principle commits us at the same time to two contradictory courses of action: that we should develop GM crops and that we should not [1], and hence the principle is 'incoherent'.

Like so many other opponents of the precautionary principle, Comstock misunderstands its role. He assumes it is an algorithm for making decisions, which is why he writes of the principle as committing us to one or another course of action.

We want to emphasise that the precautionary principle is not an algorithm for making decisions. It does not make decisions for us, but it is a principle on which to base decisions. It is a principle for assigning the burden of proof, in much the same way that the defendant in a criminal court is assumed innocent until proven guilty 'beyond reasonable doubt' [2]. This important rule reflects society's view that convicting the innocent is far worse than acquitting the guilty. It has a profound effect on the outcome of many trials, but it still leaves the jury with a lot to do. They still have to weigh up the evidence, and they have to decide for themselves what constitutes 'reasonable doubt'.

In the same way, the precautionary principle requires us to assign the burden of proof to those who want to introduce a new technology, particularly in cases where there is little or no established need or benefit and where the hazards are serious and irreversible. It is up to the perpetrators to prove that the technology is safe 'beyond reasonable doubt'. We cannot expect the precautionary principle by itself to tell us what to do about GM crops or any other new technology. Like a jury, we have to weigh up the evidence, and like a jury we have to come to a decision.

So, what is the evidence on GM crops? There is practically no evidence that they are safe, of the kind that could stand up in a court of law. A survey published last June showed that there is less than a handful of papers on the subject of safety assessment published in peer-reviewed scientific journals [3]. The vast majority consists of unpublished reports submitted to regulatory bodies for product approval, and these, far from supporting claims of safety, actually provides evidence to the contrary [4].

The published papers from the industry are no better. For example, Monsanto's study on Roundup Ready soya was seriously flawed. Two papers [5, 6] showed, among other things, significant increases in milk fat in cows and lower weight gains in male rats fed GM soya. There was also a 26.7% increase in a major allergen and growth inhibitor, a-antitrypsin in the GM soya. Monsanto had failed to submit even more damning data indicating that another allergen, a soya lectin, was increased by 100% in retoasted soya beans [7].

On the other hand, there is already plenty of evidence of actual and suspected hazards from findings reported in the scientific literature.

We summarise some of the findings giving direct evidence of hazards, omitting those giving indirect evidence of hazards. These have been reviewed extensively [8,9] and only new references are cited below.

Given the weight of evidence, it seems obvious to us that no GM crops should be planted in open fields, unless and until we can be convinced, by counter-evidence, that the risks are minimal.

But by being cautious, are we, as Comstock and others claim, running equal risks in the other direction, of losing potential benefits, or the ability to deal with needs that may appear in 50 years time? Not at all.

The biotech companies and their supporters say we need GM crops to increase yield to feed a growing world population. Norman Borlaug, father of the green revolution and prominent supporter of agricultural biotechnology, claims GM crops are needed to feed a projected 10 billion. Again, let us look at the evidence. There is no scientific report documenting that yield has been increased in GMOs compared to non GMOs; quite the contrary is the case, as mentioned earlier, yield drags are frequently reported. What about population increase? According to the United Nations Population Division, world population growth had been slowing down since the 1960s. The estimate in 1998 was that total world population will peak at 7.7 billion in 2040, then go into long term decline to 3.6 billion by 2150, less than two-third of today's number. Similarly, a FAO report published in July 2000 [14] concludes that existing technologies, not counting GMOs, will produce enough and more than enough food to meet population growth. The real problem is one of distribution, as generally acknowledged. People are starving in the midst of plenty.

What about the possibility that at some time in the future we may have to make changes in the crops we grow and that genetic engineering may be needed? Or that with more research, gene biotechnologists will be able to produce new varieties that are indeed better and safer than the present ones? Even allowing for those possibilities does not mean we have to rush ahead with the present inadequately researched and tested technology. Nor does it mean we have to accept unsubstantiated promises that GM crops will provide the answer.

Looking at all the evidence and taking seriously the precautionary principle thus lead to the following conclusion. We should continue doing basic research in molecular genetics, including research relevant to the safety of GM constructs as well as making GM plants; for example, on how to modify existing genes precisely and safely, rather than to transfer in GM constructs haphazardly. But all that should be done in the laboratory and in the greenhouse under carefully contained conditions.

There should also be major effort devoted to developing better varieties of crops by conventional breeding and to research on organic, low-input farming methods. Agroecological farming methods which use crops and knowledge adapted to local conditions have been increasing yields two, three-fold since the 1980s. They provide social, environmental and health benefits in Latin America, Africa and Asia. There are good reasons to encourage farmers to grow and sell locally crops that are adapted to local conditions, and not to pressure them into growing national or international varieties for export. Export industrial agriculture is responsible for a great proportion of the fossil fuel consumption that contributes to climate change. Furthermore, there is incalculable health bonus to be gained in phasing out agrochemicals that are known to be linked to cancers and many other illnesses.

In that way, we can be confident about feeding the world today and for the foreseeable future, and we will still stand to gain from whatever benefits GM technology may bring. The only losers will be the biotech industry, because they cannot afford to wait. The rest of us can.


  1. Comstock's note, based on his talk at the meeting on Biotechnology held in Cambridge, MA, 22-23 September 2000, is available on
  2. "Use and Abuse of the Precautionary Principle" by Peter Saunders, ISIS News#6
  3. Domingo JL. Health risks of GM foods: many opinions but few data. Science 2000: 288: 1748-9.
  4. See transcript of Dr. Arpad Pusztai's statement Chardon LL hearing, London, October 24, 2000
  5. Hammond et al, 1996, Journal of Nutrition 126, 717-26.
  6. Padgette et al, 1996, Journal of Nutrition 126, 702-16.
  7. "Buried data in Monsanto's study on Roundup Ready soybeans" by Barbara Keeler
  8. Dr. Mae-Wan Ho's statement to public hearing on Chardon LL, October 26, 2000, also
  9. See World Scientists' Open Letter and other papers,
  10. See Witness Brief by Prof. Joe Cummins to New Zealand Royal Commission on Genetic Engineering
  11. Fares NH and El-Sayed AD. Fine structurl changes in the Ileum of mice fed on d endotoxin-treated potatoes and transgenic potatoes. Natural Toxins 1998: 6: 219-33.
  12. Chiter A, Forbes JM and Blair GE. DNA stability in plant tissues: implications for the possible transfer of genes from genetically modified food. FEBS Letters 2000: 481: 164-8.
  13. "Disaster in the making" Rachel Nowak, New Scientist 13 Jan, 4-5, 2001; Also "The genie is out" Editorial, New Scientist 13 Jan, 3, 2001.
  14. Agriculture: Towards 2015/30, FAO Global Perspectives Studies Unit, July 2000

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