DiGiovanni and Kevan (2008, Environ. Biosafety Res.7: 105–108) commented
extensively on the empirical approach that I and my co-authors took in our
previous modeling of pollen-mediated gene flow in maize (Gustafson et al. (2006)
Crop Sci.46: 2133–2140). As we detailed in that original paper, gene flow
is a highly complex process that necessarily requires at least some level of
empiricism in order to adequately quantify all of the biological,
meteorological, and physical phenomena that are involved. DiGiovanni and
Kevan favor a mechanistic modeling approach, and they proposed a number of
potential advantages for such a method over our entirely empirical
technique. However, the 20 m buffers we had proposed based on our
empirical model continue to be supported by the rapidly growing body of
experimental data on maize gene flow that has now been collected in Europe
and elsewhere around the world. This does not mean there is no place for
mechanistic modeling of gene flow, but it does suggest that properly
implemented empirical approaches have a valid role to play. They offer a
degree of simplicity and practical utility that is not available from more
complicated approaches.