American Journal of Clinical Nutrition, Vol 55, 1191S-1195S, Copyright © 1992 by The American Society for Clinical Nutrition, Inc
Comparative life spans of species: why do species have the life spans they do?
TB Kirkwood
Laboratory of Mathematical Biology, National Institute for Medical Research, London, UK.
Proximate answers to questions about species longevity are to be found in
the physiological processes that regulate duration of life. But what are
these processes, and how are they themselves controlled? This leads to
ultimate, evolutionary questions about longevity. What are the selection
forces that favor one life span instead of another for a given species? To
understand the evolution of life span we need also to understand the
evolution of aging. A plausible hypothesis is that because of the
requirement for reproduction, natural selection favors a strategy that
invests fewer resources in maintenance of somatic cells and tissues than
are necessary for indefinite survival. This "disposable soma" theory
predicts that aging is due to the accumulation of unrepaired somatic
defects and the primary genetic control of longevity operates through
selection to raise or lower the investment in basic cellular maintenance
systems in relation to the level of environmental hazard.
