Evolution and dietary restriction.

Placing lifespan in the context of the life history of an organism, Alex Comfort's work has stimulated the analysis of dietary restriction (DR) and its effects on lifespan in an evolutionary context. DR results in the curtailment of energy-intensive nonfood-gathering activities, increased efficiency of food utilization, an increase in food acquisition activity, an increase in the reproductive lifespan, and an increase in the protection of genomic integrity. These result in further refinement of the Adaptive-Longevity Related Process Theory of the effects of dietary modulation to include increased protection of the genomic integrity of cells that result from delayed reproduction, and increased ability to compete for available food. These effects are discussed in the context of the "spacecraft" metaphor for the evolution of senescence. Also, the apparent paradox that increased body weight seems to be directly correlated to survival across species and inversely correlated to survival within a species is discussed in light of the importance of the cephalization index (a modified ratio of brain weight to body weight) for longevity.