Why Do We Age?
Why Do We Age?
In 2004, the amazing ‘Flying Phil’ Rabinowitz broke the world 100 m sprint record for a centenarian, setting a time of 30.86 s and beating the previous world record time by over 5 s. Despite this impressive statistic, most 20 and 30 year-olds can readily run at these speeds when dashing for a bus, and the overall world record for 100 m currently stands at 9.69 s (set by Usain Bolt at the age of 21). Age-related degeneration in bodily function is familiar to all of us, and is known as ‘senescence’, or more colloquially, as ‘ageing’. Of course, this loss of physiological functioning not only impairs our ability to run: as individuals get older they typically experience an increase in the likelihood that they will die, and also a decrease in fecundity. The incidence rates of cancers and heart attack, for example, are considerably higher in older than in younger individuals. For these reasons, ageing has been dubbed ‘the most potent of all carcinogens’, but it has also long been considered as one of the world’s worst diseases (‘senectus enim insanabilis morbus est’—a sickness for which there is no cure). . . . Live long and prosper? . . . Organisms die for all sorts of reasons. They may get run over by a bus, they may be eaten by a predator, or they may succumb to a lethal disease. However, even if individuals survive all of these ‘extrinsic’ challenges, then the odds are that they will begin to experience the signs of senescence. While being eaten by a predator is unfortunate, it is also eminently understandable as a cause of death. Natural selection will tend to act on individuals to reduce the likelihood of this extrinsic mortality (for instance, by promoting higher vigilance or the development of some form of defence) but death from accidents, predators, and parasites cannot be completely avoided. Ageing, however, poses much more of a dilemma for evolutionary biologists. In particular, one might expect that those individuals who managed to slow down the ageing process would leave more offspring, so that natural selection would favour extreme longevity.
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