Studies on the effects of the aging process on the physiological systems should ideally be conducted on the same individual throughout its life span. But, in practice, the profile of an age-specific change is generally procured by sampling different members of a population at various ages, because measurements at the cellular and molecular level often necessitate the killing of the experimental animals. However, due to individual variation, the pattern obtained from population averages may not be identical or in sufficient accord with the data gathered from the same individual at different ages. This study examines the relationship between individual and population life-span patterns of any age-specific biological parameter (ASBP). The effects of individual variation and selective mortality on the pattern of an ASBP based on population averages has been elucidated. A procedure is presented by which the individual variation in a population can be quantified using mortality data. This procedure can also be employed to distinguish between the changes occurring due to aging alone, and those superimposed by individual variation and selective mortality which would allow comparisons between the predicted and the actual experimental results obtained by sampling of the populations. © 1979.
