Human technology relentlessly gives the human race increasing power both to prevent harm through such things as the conquering of disease, and to damage human health and the environment due to increasing impacts on ecological systems. Because of the complexity of ecological systems, the power of technology for harm as well as good, and the increasing speed of potential adverse impacts on human health and the environment, policy-makers are frequently confronted with the need tomake decisions in the face of scientific uncertainty about issues that have potentially huge and sometimes catastrophic impacts. Frequently decisions on these issues will affect the economic interests of those who profit from the activities that threaten human health and the environment. These interests invariably pressure policy-makers not to restrict the activities in question unless there are high levels of scientific proof that the activities will actually cause great harm.