If we assume that adult life span and age-at-maturity are described correctly by quarter power allometries across (typical) mammal species, we are tempted to look for some fundamental explanation. The explanation must acknowledge that within-species growth is sigmoid and not a power function at all, and that natural selection probably sets the age at maturity in the face of externally imposed mortality, while also allowing some mortality adjustment due to internal factors. This paper develops hypotheses to account for the above scaling rules and it predicts the numeric values of several new dimensionless numbers that interrelate growth, mortality and investment in cellular maintenance
