Debating the Precautionary Principle: “Guilty until Proven Innocent” or “Innocent until Proven Guilty”?

On May 20, 1999, Nature published a brief report on an experiment performed by researchers at Cornell University that indicated that pollen from genetically modified (GM) Bt corn (Zea mays) could kill the larvae of monarch butterflies (Danaus plexippus). In laboratory tests, caterpillars fed milkweed (Asclepias curassavica) leaves dusted with pollen from a Bt corn hybrid showed retarded growth and increased mortality. “These results,” the authors stated, “have potentially profound implications for the conservation of monarch butterflies” (Losey et al., 1999). In a press release announcing the publication in Nature, the principal investigator on the Cornell study, John Losey, had expressed due caution: “Pollen from Btcorn could represent a serious risk to populations of monarchs and other butterflies, but we can’t predict how serious the risk is until we have a lot more data. And we can’t forget that Bt-corn and other transgenic crops have a huge potential for reducing pesticide use and increasing yields. This study is just the first step, we need to do more research and then objectively weigh the risks versus the benefits of this new technology” (Cornell News, 1999). Such caution was wasted on Greenpeace International. The day the findings of the Cornell study were published it already demanded that authorities in the United States, Argentina, Canada, and the European Union take immediate action and prohibit the growing of genetically engineered maize crops. The environmentalist nongovernmental organization (NGO) reiterated its earlier call for a ban on all releases of genetically modified organisms (GMOs). Less than a month later, in a media-oriented action, members of Greenpeace dressed up as butterflies confronted a meeting of European Union environment ministers held in Luxembourg, carrying banners demanding “Give butterflies a chance.” In Europe, their campaign apparently found resonance among the authorities: The European Commission decided to freeze the approval process for new Bt maize varieties. The Cornell study did not show that monarch butterfly populations in the wild were actually endangered by Bt corn. However, when Monsanto and Novartis, the companies that sold Bt corn at that time, correctly pointed out that the detrimental effects had so far only been shown in the laboratory, Greenpeace branded them as irresponsible. A spokesperson declared: “Such reactions are the precise opposite to precaution and follow the same pattern of denial these companies have employed for decades, when health and environmental effects of their chemical pesticides were exposed. However, in the case of these GMOs we are talking about living toxins that can reproduce in nature and transmit their dangerous traits to wild species. We cannot consider GMOs harmless until harmful effects are fully proven (sic)” (Greenpeace, 1999a). (The last sentence is obviously a—Freudian?—slip of the tongue and should be read: “We cannot consider GMOs harmless until the absence of harmful effects is fully proven.”) For Greenpeace, not just monarchs were supposed to be endangered. The NGO drew up a list of over 100 species of butterflies that it believed could be harmed by GM maize. It accused biotech companies and regulatory authorities of fully ignoring these risks (Greenpeace, 1999b). More recent field research performed in the American Midwest, however, seems to indicate that monarch butterfly populations are hardly affected, if at all, by the large-scale cultivation of Bt maize in this region (Ortman et al., 2001). The monarch butterfly case is only one among many occasions in which the so-called Precautionary Principle (PP) has been invoked to advocate preventative action to forestall possible harm even before the likelihood or the possible extent of the latter has been scientifically well established. This principle is highly contested. With many other environmentalist NGOs, Greenpeace champions its adoption as a central principle of international law against tenacious opposition from the United States, Canada, and Australia (Greenpeace, 2002). The principle is also at issue in recent World Trade Organization trade disputes between the United States and the European Union. But why does the PP play such a central role?