The remarkable advances in mapping of genomes have made it feasible to search among the hitherto anonymous polygenes of complex systems for loci of intermediate effect size (quantitative trait loci-QTL). Pursuing the strategy of identifying these QTL in complex systems will open the possibility of exploring the genetic architecture and the anatomical, physiological, biochemical, and molecular mechanisms underlying the phenotypes under investigation. One study (Gelman et al., 1988) has pioneered the exploration of QTL in the study of aging. Their engaging results, dealing with age at death as the endpoint measure, portend the power of the search for quantitative trait loci in aging processes.