Starvation in humans: evolutionary background and contemporary implications.

Although there is extensive evidence that caloric restriction (CR) extends lifespan in several species the evidence base for humans is weak. We are still at the stage of applying inductive reasoning and of framing hypotheses to be tested. It is known that a genetic background contributes about 25% to the variation in human longevity, but thought unlikely that any genes conferring longer lifespan have been positively selected to do so. It is more likely that any such benefits are unintended consequences arising from other adaptations. If there is an association between CR and longevity in humans it may have been selected by previous exposures to famine. This paper briefly reviews the historical evidence on the extent and frequency of famines in human history. It is concluded that starvation has been one of the major selective pressures on the human genome and has left abundant evidence of adaptive survival traits. Many of these are mediated through effects on reproduction. However, interpretation of the possible links between these energy-sparing mechanisms and any association between CR and ageing is handicapped by an absence of data on the latter and will remain a matter of debate for many years to come.