Did you know that vitamin C isn’t essential to all animals? However, it is for us humans. It isn’t a necessary component of diet, at least for all mammals with the exception of guinea pigs, fruit eating bats, the red vented bulbul bird and primates —which includes us. All other species make their own.
This they do by converting glucuronic acid derived from glucose into ascorbic acid (C6H8O6). Three enzymes are required to make this conversion. One of these enzymes, or part of the enzyme system, is missing in primates. Irwin Stone proposed, in 1965, that a negative mutation may have occurred in these species so as to lose the ability to produce vitamin C. In primates, this is thought to have occurred in the region of 25 million years ago.
Unlike other vitamins, vitamin C is required in large amounts, which could only be supplied by a tropical diet high in fruit and other vegetation. If sufficient vitamin C could be obtained from such a diet, the quantity of glucose normally used to synthesize vitamin C could be channelled towards energy production. This could conceivably have been an advantage for primates or other species.