The effect of autologous and environmental wear and tear on genes and gene products will be considered in systems renewed by self-replicating stem and precursor cells as well as in systems that do not have the capacity for self-renewal. Aging will be discussed in terms of speciation and in terms of health-span differences between individuals of the same species. The analysis of speciation involves early as well as late-acting genes. The intraspecies analysis is primarily concerned with the second half of life and thus is not affected by selective pressures. Analysis of individual aging is concerned with health span, qualified by identification of the particular system that is responsible for the limit of health span in subpopulations; it depends on a subset of allelic products of many genes and their relative functional capacity. The identification of such alleles can provide the starting point for reverse genetics. Results will be presented, which have been obtained by analysis of age-related events in inbred mice, where regulation, involved in degenerative disease of old age, can be studied in groups of individuals with a relatively constant genetic background. It should be possible to identify appropriate probes for degenerative diseases of old age that can be used for detection of corresponding human genes. Worldwide demographic changes have created the need for a new type of public health policy. To respond to this need, we should learn how to identify individuals at risk from degenerative diseases of old age and how to treat them preventively.