The rodenticide warfarin was originally introduced during World War II and has continued since then. Although it was initially very successful, its effectiveness has lessened over time because of an increase in resistance among some target populations of rats. For instance, among Norway rats in Great Britain, resistance results from an otherwise harmful mutation R in a gene in which the normal sensitive allele is denoted S. In 1985, R. M. May (Nature 315:12-13) calculated the relative fitness of the SS, SR, and RR genotypes in the presence of warfarin to be 0.68, 1.00 and 0.37, respectively. The reduced fitness of the RR genotype appears to result from an excessive requirement for vitamin K. Required:
In the presence of warfarin, what is the value of the selection coefficient s for this population of rats?