with David Quist - The Mexican Maize scandal

by GRAIN | 22 Apr 2003

David Quist was one of the authors of the first study to report the contamination of one of the centres of genetic diversity with genetically modified (GM) crops. The paper erupted into what has become known as the ‘Mexican maize scandal'. Here GRAIN talks to Quist about the aftermath of the volcano and the implications for farmers, scientists and consumers.

GRAIN: What is the story behind the study that ignited such controversy around the world?

David Quist: The story began in a small laboratory in Oaxaca in the highlands of Mexico. My professor Ignacio Chapela had been serving as a scientific director for four indigenous communities which had banded together to manage their natural resources. I had been working with them on another project, but would also help them with technical workshops. These were all indigenous-run projects with the ideas and initiatives coming from the communities themselves. One question that came up for them was whether GM crops were an issue they should be concerned about. We said that Mexico had a moratorium on planting transgenic crops at the time, so it should not be something they needed to worry about immediately, but it might be something they would want to consider down the line as the situation might change.

The groups wanted to learn more, so on one of my trips there, I brought some transgenic corn with me and we ran a workshop on testing for transgenic DNA. We needed a transgenic-negative control, and what better place than the highlands of Oaxaca, the birthplace of maize? We worked out a sampling protocol, did the DNA extraction and ran the analysis. The day before the workshop I ran a test sample and couldn't believe the results - some of the native corn tested positive. We had also taken a sample from the local food agency, which also tested highly positive. These food agencies distribute food in every village throughout the country, and while the maize is supposed to be used only for consumption, there is no label on it saying, “Do not plant this”. This means that in every village in Mexico has these point sources of potential contamination.

We went back to the lab, did some new sampling, and more widespread and stringent analysis, the results of which became the Nature paper. [1] But first we felt we had to go to the Mexican government to let them know what we had found, even if it might compromise our ability to publish the work. In the Nature paper, we made two main statements. The first was simply that genes from the transgenic corn had migrated into native populations. For this we used a technique called PCR, which is widely used to amplify the DNA of interest into sufficient quantities to identify and analyse it. It is the standard tool for GMO identification used by regulatory agencies throughout the world for accepting or rejecting shipments of GM-free grain. The second statement was more exploratory and used a new technique called inverse PCR that allows us to look more specifically at where in the plant's genome the transgenic DNA is located. To our surprise we found it in a diversity of places within the native maize genome. There could be various explanations of why this might be, one of which is that the transgenes had become reinserted through recombination. [2] We felt there was sufficient evidence to suggest that this explanation might be true, so we published it. And that is part of what science is: proposing novel explanations from observed patterns in data, from which further work is done to substantiate or refute the initial findings. We knew this was a bit novel, a bit “out there”, because there was no previous science behind it and no-one was doing it. At least there was nothing in the peer-reviewed literature, but it wouldn't surprise me if companies have done this kind of work without publishing it, if they did not like what they saw. People responded by saying that there is no evidence that this kind of gene shuffling is what is going on, but no-one has looked, no-one has asked these questions before. We wanted, and expected, a strong reaction, but not in the way it came.

GRAIN:A year and a half on from the publication of your paper in Nature, what is your perspective on why there was such a strong reaction to this paper? [3]

DQ: The first wave of response was to trivialise the first statement that we made, which simply said that the transgenes were present in the native landraces. The proponents of biotech were saying ‘we know that commercial varieties cross with local varieties all the time - no big deal.' What created a bigger response was what we were exploring in looking at what those genes were doing once they got there. We were going against the propaganda of the industry which says that this technology is precise, this technology is stable. We were suggesting that it is unstable, which infuriated the pro-biotech community. Another reason was that the timing of these findings was really bad for the industry - our findings were biting up against the debates on the moratoria in Europe, Mexico and Brazil. It was a huge PR disaster. In addition, the industry was in a downturn economically. When you look at where the strongest reaction was coming from, there were very significant links to Berkeley and the Berkeley-Novartis deal that was signed five years ago. [4] At that time a number of groups were raising concerns about what it meant for academic freedom, student education, and so on. Dr Chapela was a leading opponent of the signing of the agreement within the college and I was also involved in a vocal group opposing the deal called Students for Responsible Research. I don't think it is insignificant that the most vocal detractors of our paper came from the camp that supported the Novartis deal back in 1998

From Iowa to Oaxaca: Easy passage for the Bt gene

Maize is the most important crop in Mexico. About 1.5 million hectares of the maize grown consists of hybrid varieties (developed mainly by transnational companies), 0.9 million hectares are open pollinated varieties (developed by the public sector and small companies) and the remaining 5.5 million hectares are planted to local land races. Some 68% of the maize grown in Mexico is used directly for human consumption.
Maize is also an extremely important crop to the US, the world's largest maize producer and exporter. In 2000, Mexico was second only to Japan as a market for US maize, absorbing 11% of US exports. Some 24% of total corn consumption in Mexico now comes from the US. Since 1996, US maize exports to Mexico have increased as exports to Europe have decreased, owing to Europe's rejection of GM maize. Of the 5-6 million tons of maize that were imported to Mexico in 2000, 30%-40% was transgenic, but was not segregated or labelled. That same year Mexico had exactly the same amount of domestic maize rotting away, unused.
The maize that comes into Mexico gets distributed through welfare food systems around the country. It is subsidised from beginning to end by US taxpayer dollars. Incredible amounts of money go into the production of this grain that receives subsidised water, soil, machinery and oil; is subsidised in international markets; and subsidised again in Mexico through distribution. It just floods the country.
When you talk to a farmer in Oaxaca, they say, “It costs six pesos to grow seed; I can buy it for four.” The farmer is paying out of his or her pocket to plant his or her own seed. Small wonder that transgenic maize is so widespread in the fields of Mexico..

Sources: “Dr Ignacio Chapela on Controversy, Corn and What's Really at Stake in Mexico”, Global Pesticide Campaigner, August 2002; Chantal Carpentier and Hans Herrmann, Maize and Biodiversity: The Effects of Transgenic Maize in Mexico: Issues Summary, CEC,

What has been the effect of all this on the work you are doing, and has there been follow-up work?

DQ: The contamination of local maize varieties was a completely unexpected discovery. I wasn't working on maize when it happened, and I wasn't looking for this when it happened. My training is in mycology. However, since this study I have switched to asking questions about gene flow and how genes move in the environment, both horizontally and vertically [5] and I am doing some follow up work in that area. Transgene ecology is a fledgling field. There are a couple of other institute, such as the Norwegian Institute of Gene Ecology [6] and the New Zealand Institute of Gene Ecology, [7] which are doing some great work, but I don't think they are working on agricultural issues to any great extent. And unfortunately, when a particular branch of science becomes politicised, it becomes a hot potato that scares others away from working in the field. In the case of maize, who is asking the questions about the implications for farmers, human health, and global food systems? In Mexico, those questions have still to be answered. To its credit, the government is doing follow up work to look at the scale of transgene contamination around the country, but it has yet to employ any kind of strategy to try and manage it or ascertain its significance.

On a different tack, a number of civil society groups, spearheaded by Greenpeace, [8] applied in April 2002 to the North American Free Trade Agreement's Commission for Environmental Cooperation (CEC) to investigate the issue. CEC's mandate is to look at the environmental impacts of the NAFTA agreement or environmental issues that will impact the NAFTA agreement, and accepted the challenge. But I'm very sceptical that, given the composition of the committee appointed to investigate the issue and also the nature of the CEC's mandate, that the investigation will have the political fortitude to state anything other than ‘there is no evidence that this poses any harm, therefore we should continue importing maize from the US'. However, there is no way they could make a statement like that from a scientific, ecological point of view without conducting rigorous science, which I do not think they are not doing, at least at this point. They are just going to come up with the usual fallback position that absence of evidence is evidence of absence, which is scientifically fallacious.
The Mexican government did a follow-up study in response to your findings. What kind of research did they do and how was their research received?

In the first round, samples were taken from 22 communities in Pueblo in Mexico, 15 of which tested positive using the same PCR technique that we used. Since then, they have done a much more expansive study in terms of sampling and techniques. The government submitted its results to Nature, but its paper was rejected in October 2002. [9] Two reviewers rejected the paper for opposite reasons. One said that the findings were “obvious” (having already been reported before in Nature), while the other said they were “so unexpected as to not be believable.” To have two reviewers making such drastically different interpretations of the same data is interesting - there is obviously a story behind that.

GRAIN:The Mexican Government established a moratorium on planting GM corn in 1998, so how did the transgenic maize get there?

DQ: In our local setting, we suggested two possible sources of contamination - very local sources (such as the food agency maize) or that it was wind blown from the industrial maize planted in the valley about 60 miles away in Puerta Vallerta. The first explanation seems the most likely: farmers have admitted that they have planted food agency maize. The food agency maize we tested was highly transgenic - its positive signal was as strong as our transgenic positive. There are also a number of agricultural research stations that have been doing field tests of GM corn in open field plots before and after the moratorium came into effect.

GRAIN:What are the implications of your work for farmers in Mexico, and small farmers in particular? What are the biggest threats to them?

DQ: One is all the unknowns - the ecological significance, the effects on human health
and genetic diversity, for instance. Those kinds of studies should have been done already, but weren't. We just don't know. The second is the unresolved questions related to liability and intellectual property issues. If Monsanto goes into the highlands of Oaxaca and finds its genes in a farmer's field, who shoulders the liability – the farmer or the corporation? In the case of Percy Schmeiser, the liability fell with the farmer (see p 10). But according to the ‘polluter pays' principle, if the company has compromised the farmer's ability to produce for certain markets, then the company should be liable. The third major threat to farmers is the loss of markets owing to the pollution of their maize crops.

GRAIN:What about the wider implications?

DQ: I am concerned about the impact on science. It is unfortunate that the debate became so politicised and the real issue was discredited because of some disagreements over the interpretation of the I-PCR data. While there was a lot of noise made about the paper, there has been what I call “scientific silence” over it: no-one is doing the follow up work to refute or support our findings and no-one is asking what the implications of them are. People have reacted defensively: because they don't see what they expect to see, they call our results “erroneous”. This kind of approach is a disservice to science. What we are seeing more and more is that the science of substantiating facts is overriding science as a process, which is all about questioning and re-examining our assumptions, in order to lead us to a better understanding of reality. The way that the debates are framed and the inability of corporate science to re-examine its paradigms are compromising good science. What message does this send to other scientists who make the ‘wrong' findings or ask the ‘wrong questions', ie those that go against the science of the corporate agenda?

The events that have occurred also raise a lot of questions about the true objectivity of the peer-review process in scientific reporting. Science recently published a fairy tale story about the success of Bt cotton in India, [10] despite the fact that Bt cotton is failing miserably all over India. Nature's handling of our paper suggests that it was under pressure from the industry camp. As the heat built up, the journal did not handle things very well and made a lot of people angry, on both sides. Two of the three referees said that they did not challenge the main conclusions of our paper, but suggested writing a correction to part of it. Why didn't the editor make this clear, point out that there were some issues of contention over certain aspects of our findings, and put out calls for more work on the subject? Why the need for a disavowal? And why were most people left with the impression that the paper had been retracted, when it was not? A hallmark of good science is in asking exploratory questions - just as we were doing. We weren't out of step with that, but the response we received was out of step with the way that normal scientific discourse should happen to advance scientific knowledge. Situations like this call into question whether these journals can continue to be looked to as a reliable source of objective science.

David Quist

Since 1998, David Quist has been a graduate student in the PhD Programme in Environmental Science, Policy and Management at the University of California, Berkeley, California. A mycologist by training (someone who studies fungus), he made the discovery about the contamination of maize varieties in Mexico quite by chance. Since the study that was published in Nature, his work has become more focused on transgene ecology - ie how genes move about in the environment. David Quist can be contacted by email at



David Quist and Ignacio Chapela, “Transgenic DNA introgressed into traditional maize landraces in Oaxaca, Mexico”, Nature Vol. 414, pp541 - 543 (2001) Chapela_Research.htm


ie the transgenic material had become fragmented and scattered throughout the genome


For a fuller insight into what became publicly known as ‘the maize scandal', go to


Under this agreement, Novartis provided $25 million to the Department of Plant and Microbial Biology (a third of the department's income) in return for first right to negotiate licenses on roughly a third of the department's discoveries (including research funded by public money) and 2 out of 5 votes on the committee that determines how the department's money is spent.


Vertical gene flow is the way in which genes are passed on from parent to offspring through cross-pollination. Horizontal gene flow is the direct uptake and incorporation of foreign DNA into cells




Greenpeace press release, “Mexican Groups, Greenpeace Launch NAFTA Appeal To Force Action Against Genetic Contamination”, April 24, 2002, 2002/04242002text


Food First Press Release, “Nature Refuses to Publish Mexican Government Report Confirming Contamination of the Mexican Maize Genome by GMOs”, October 24, 2002,


Matin Qaim and David Zilberman, “Yield Effects of Genetically Modified Crops in Developing Countries”, Science Vol. 299: 900

Author: GRAIN
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