Food, reproduction and longevity: is the extended lifespan of calorie-restricted animals an evolutionary adaptation?

Calorie restriction results in an increased lifespan and reduced fecundity of rodents. In a natural environment the availability of food will vary greatly. It is suggested that Darwinian fitness will be increased if animals cease breeding during periods of food deprivation and invest saved resources in maintenance of the adult body, or soma. This would increase the probability of producing viable offspring during an extended lifespan. The diversion of limited energy resources from breeding to maintenance of the soma is seen as an evolutionary adaptation, fully compatible with the 'disposable soma' theory of the evolution of ageing.