The regulation of health and environmental risks has generated transatlantic controversy concerning precaution and the precautionary principle (PP). Conventional wisdom sees the European Union endorsing the PP and proactively regulating uncertain risks, while the United States opposes the PP and waits for evidence of harm before regulating. Without favouring either approach, this paper critically analyses the conventional depiction of transatlantic divergence. First, it reviews several different versions of the PP and their different implications. Second, it broadens the transatlantic comparison of precaution beyond the typical focus on single-risk examples, such as genetically modied foods. Through case studies, including hormones in beef and milk production and mad cow disease in beef and in blood donations, as well as reference to a wider array of risks, the paper demonstrates that relative precaution varies enormously. Sometimes the EU is more precautionary than the US (such as regarding hormones in beef), while sometimes the US is more precautionary than the EU (such as regarding mad cow disease in blood). Thus, neither the EU nor the US can claim to be categorically 'more precautionary' than the other. The real pattern is complex and risk-speci c. Third, the paper seeks explanations for this complex pattern in ve sets of hypotheses: optimal tailoring on the merits, political systems, risk perceptions, trade protectionism, and legal systems. None of these hypotheses fully explains the observed complex pattern of relative transatlantic precaution. The paper concludes that differences in relative precaution depend more on the context of the particular risk than on broad differences in national regulatory regimes.

Regular, institutionalized updating and review are essential

No abstract

¹¹ The literature on horizontal legal borrowing (across states) is extensive; the classic is Alan Watson, Legal Transplants: An Approach to Comparative Law (2nd edn) (Athens, Ga: University of Georgia Press, 1993). ¹² A framework of legal borrowing that adds the vertical dimension (between states and federal and international bodies) is developed in Jonathan B Wiener, 'Something Borrowed for Something Blue: Legal Transplants in the Evolution of Global Environmental Law' (2001) 27 Ecology LQ 1295. ¹³ A useful history of the connections of Better Regulation to these three elements of the EU platform is provided in Ragnar Lofstedt, 'The Swing of the Regulatory Pendulum in Europe: From Precautionary Principle to (Regulatory) Impact Analysis' (2004) 28 J Risk & Uncert 237-60. ¹⁴ For further discussion on 'hybridization' of legal ideas and the counterpart concepts in evolutionary biology, see Jonathan B Wiener, 'Whose Precaution After All? A Comment on the Comparison and Evolution of Risk Regulatory Systems' (2003) 13 Duke J Comparative & Int'l Law 207, 254-61. An overview of evolutionary biology concepts applied to legal evolution is Simon Deakin, 'Evolution for Our Time: A Theory of Legal Memetics' (2002) 55 Current Legal Problems 1-42. See also sources cited in nn 29-31 below on legal borrowing and diffusion. ¹⁵ See Wiener, n 14 above (noting failure of hybrids until new niches open); Willam Reppy, 'Eclecticism in Choice of Law: Hybrid Method or Mishmash?' (1983) 34 Mercer L Rev 645 (criticizing eclecticism as unpredictable and standardless, while endorsing careful construction and transparent selection of new hybrid methods). Moreover, diffusion itself can sometimes undermine incentives to innovate or can invite fads.