Unintelligent Design And Vitamin C Deficiency

Vitamin C is essential for normal health. In fact, if you don't have enough vitamin C in your diet, you will die of an especially nasty disease called scurvy. Vitamin C is a relatively simple organic molecule chemically called ascorbic acid. Fortunately, a normal varied diet usually contains enough vitamin C, especially one containing fresh fruit and vegetables because plants manufacture vitamin C. When the cause of scurvy, which was a major problem amongst sailors on long ocean voyages, was discovered in 1747, simply adding lime juice to their diet cured it almost overnight, hence the British sailors who travelled to and from the New World earned the nickname 'Limeys'.

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

The daft thing is that, just like the vast majority of animals which do make their own ascorbic acid, we, along with a small number of other mammals, have the genes to make it, and our liver cells contain three of the four enzymes for making it out of glucose, just like all the others. The only problem is that the fourth (L-gulonolactone oxidase) is missing because the gene for making it is broken! A small copying error millions of years ago effectively turned off something which is essential for many other animals.

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.

And those other mammals I mentioned earlier? Many of them are primates occupying branches on our limb of the evolutionary tree. If we plot these, together with what we know of their relationship to one another from fossil records and genetic evidence, the pattern is quite striking. All those who occupy one of the two branches which diversified from a common ancestor some 60-63 million years ago have the same genetic defect. The rest still make vitamin C in the perfectly normal way and don't need it in their diets.

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?

Further reading:

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.

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