A. Brooks et al. report that mortality increased exponentially for a cohort of 180,000 nematodes of the species Caenorhabditis elegans of the single genotype TJ1060 [spe-9
)]. A closer look at the data reveals that from days 5 through 8 mortality increased at a rate of 0.58 +/- 0.0004, which is more than twice the rate thereafter (0.21 +/- 0.02). Such a "biphasic pattern," with death rates increasing rapidly at younger ages and more slowly at older ages, was also found in a genetically heterogeneous population of 79 recombinant-inbred (RI) strains.