Gene flow is not unique to genetically modified (GM) crops, but the possibility of the spread of transgenic DNA to wild and domesticated relatives raises a new set of issues for scientists and policymakers to consider. Unfortunately, we are still too often unable to quantify the risks of ecological damage associated with gene flow. This is due partly to the huge breadth of knowledge required to assemble a comprehensive risk assessment. For example, many scientists active in research on the mechanics of gene flow nevertheless lack a deep understanding of what is required to identify,...