Recommended Daily Allowances (US RDA) of the Food and Drug Administration for ascorbic acid are higher than Recommended Dietary Allowances (set by the Food and Nutrition Board) for adults. There is a 6-fold margin between the requirement to prevent scurvy and the US RDA. The high requirement reported for the rhesus monkey may be needed to compensate for oxidative catabolism of ascorbic acid in this species. The rate of production of ascorbic acid, in mammals that synthesize it has been listed as 3-19 g/70 kg per day. If this high rate of synthesis represents the requirement of such animals, mutations that caused a loss of ascorbic-acid-synthesizing ability would be eliminated by natural selection on diets that failed to supply these large quantities. The loss of ascorbic-acid-synthesizing ability by human beings could indicate a low requirement, which has enabled our species to spread to regions of the earth where dietary sources of ascorbic acid are poor.