The practical implications of increasing human life expectancy

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Abstract
Declines in mortality in the past 200 years are a result of our ability to modify forces of natural selection that have been operating on our species for thousands of years. In this paper I examine these important changes from a multidisciplinary perspective that combines the fields of evolutionary biology and demography-referred to as biodemography. I contend that evolutionary theories of why senescence occurs can provide the theoretical basis for a more thorough understanding of the phenomenon of human ageing. From this perspective it is anticipated that senescence is inevitable in all sexually-reproducing organisms and that when extended survival beyond the reproductive period is achieved for a population, further declines in mortality and gains in life expectancy are limited. This hypothesis has important policy implications for a modern medical paradigm that is currently focused on postponing or eliminating fatal senescent diseases. Finally, in a discussion of genetic heterogeneity and natural selection it is suggested that extended survival results in increased heterogeneity and this in turn may create the opportunity for new senescent diseases to appear at later ages. Furthermore, it is possible that the recent introduction of antibiotics may force the emergence of more virulent strains of micro-organisms that prey on humans. It is suggested that the time has come to view human ageing from a multidisciplinary perspective that combines an understanding of senescent processes at all of the levels of biological organization, from the molecule to the population.

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