Growth negatively impacts the life span of mammals

A negative intraspecific relationship between growth and longevity was proposed in the early 20th century. Indeed, stunting the growth of rodents by restricting their food dramatically extended life span. Subsequently, however, the hypothesis that growth exacerbates aging rates fell into disfavor. Contributing to this was (a) the establishment of a positive relationship between body size and longevity interspecifically, (b) purported antiaging impacts of growth hormone, and (c) the fact that the longevity of even mature rodents that had completed growth was extended by dietary restriction. Furthermore, intraspecific analytical studies failed to provide any clear resolution. This article presents the first global analyses of maximal longevity versus maximum mature mass for laboratory rats and mice, based on a relatively comprehensive compilation of research across the 20th century. Peak body mass (which reflects juvenile growth rates) was negatively associated with longevity within both species. Proximal mechanisms for impacts of growth on longevity appear congruent with the free radical and immunological theories of aging.