Food restriction, ionizing radiation, and natural selection.

It is proposed that the allocation of energy in the animal body is modulated automatically by the endocrine system which through one or more centers responds directly to the oxygen radical flux (or an appropriate surrogate) derived from the metabolism of the ingested food. It is also proposed that energy to maintain temperature as well as reproduction and the reproductive capacity are the main sources of oxygen radicals that may be the direct cause of aging. Energy used for gathering food, resisting predators, play (i.e., most voluntary muscle action), contributes little to aging. The diversion of energy from basal metabolism and reproduction to muscular work when demanded by reduced food supply should, therefore, lead to an increased lifespan potential and an increased variance in the lifespan of a population. The change in variance favors production of offspring with longer lifespans, lower reproductive and basal metabolic rates and larger size potential. The reverse process occurs when food becomes abundant. The introduction into the body of oxyradicals, as by whole body irradiation with X or gamma rays should, therefore, mimic the ingestion of extra food and result in similar changes. At low radiation exposures the results are seen as seemingly beneficial (hormetic) effects in animals. It is shown here that some human populations seem to show evidence of the described adaptation to differences in food supply.