In his long and distinguished career, James F. Crow has studied a variety of traits in Drosophila. Crow has investigated the genetics of DDT resistance, measured the effects of minor mutations on the overall fitness of populations, and described the behavior of mutations seem to evade the expected rules of natural selection. Research on Drosophila led to broader questions about the overall mutation rates in various species, including human beings, and the analysis of how differences in mutation rates are related to sex and age. Such investigations also provide an opportunity to assess the kinds of genetic changes that exhibit a relationship to differences in age and sex. Crow is recognized as an expert on the genetic effects of low level ionizing radiation. In addition to his studies of mutation rates in human beings, Crow remains interested in the genomic rate of slightly deleterious mutations in Drosophila and...