Loss of the ability to synthesize vitamin C

Linus Pauling held that loss of the ability to synthesize vitamin C in the forerunners of humans was an evolutionary error that had best be compensated for in humans by mega-dosages of vitamin C. The difficulty with this view is that the forerunners of humans after the loss of the gene required to synthesize vitamin C had much less vitamin C available in tissues than before the loss. Given huge decreases in vitamin C bioavailability were a great disadvantage in terms of evolutionary fitness then the gene would not have been lost or at least would have once again been selected for. The animal forerunners who lost the ability to synthesize vitamin C were eating lots of fruit but were still getting a lot less vitamin C after the loss of the gene. Gulonolactone (L-) oxidase, the lost gene, is widely expressed in rats. Animals who synthesize vitamin C can synthesize huge amounts of vitamin C.

Even with fruit trees all around the loss of the gene to synthesize vitamin C would not have been a neutral mutation given the high levels of vitamin C in tissuses with the gene. The loss of the gene could not come about through genetic drift in a high fruit environment. A high fruit environment could have been permissive which is not to say that the loss of the gene and lessened bioavailability of vitamin C in tissues did not enhance evolutionary fitness.

Loss of the gene to synthesize vitamin C apparently had some evolutionary advantage which argues against supplementing with much more than RDA amounts of vitamin C now.

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