So, what about animals which don't eat lots of fruit and vegetables, animals like carnivores, or those who eat a fairly plain diet like many herbivores whose diet might or might not contain vitamin C? Not a problem for them because their livers manufacture ascorbic acid. Birds, and many other animals produce it in their kidneys.
Which begs the question: why doesn't our liver produce ascorbic acid if it is so essential for us?
|Biochemical pathway for producing ascorbic acid from glucose|
But why didn't that get quickly eliminated from the gene pool?
Almost certainly because of the alternative way to get vitamin C, and the one we now use exclusively, by eating food with enough of it. It almost certainly arose in an early ancestor whose diet was rich in fresh fruit and vegetables. Those who didn't make their own vitamin C were now saved from the need to get rid of the excess, so not making it might well have been an advantage in an environment in which their food contained enough of it. Even today, many of the members of our limb of the evolutionary tree have a diet which is mainly or wholly comprised of ripe fruit and leaves.
|Chart of the Fossil Record of the Primates with the Occurrence of Active L-Gulonolactone Oxidase in the Livers of Living Primates.|
All of this is, of course, fully understandable in terms of Darwinian Evolution by Natural Selection and descent with modification, without needing to invoke magic and in which neither intelligence nor design played any part.
Can any Creationist explain why an intelligent designer would provide the mechanism for making vitamin C in our livers, and then break it, and why it would do the same in other species which just happen to look like they share a common ancestor with us which lived some 60-63 million years ago?
The Natural History of Ascorbic Acid in the Evolution of the Mammals and Primates and Its Significance for Present Day Man, By Irwin Stone
Vitamin C Deficiency In Humans: An Issue Of Evolution.