Vitamin C Loss Is Not Evolution’s Gain
Evolution predicts gain of function; genetic entropy predicts loss of function. A gene that helps synthesize Vitamin C provides a test between the two views. Is there evidence for the origin of this gene? Or does the mutation history show loss of function spreading by entropy over various lineages of mammals? A recent pro-evolutionary paper cannot ignore the losses, but tries to give evolutionary explanations anyway.
Humans are among vertebrates that have lost the ability to synthesize Vitamin C and must obtain it from diet. Other scurvy knaves include some bats, some birds, some fish, guinea pigs and anthropoid apes like chimpanzees. In those cases, loss of function of one gene named GULO prevents the final step in Vitamin C (Vc) synthesis; otherwise, the GULO gene is highly conserved among mammals. A team from the UK and China examined bats as a test case to determine what led to the loss, and published their results in PLoS ONE.1
The authors state, “The ability to synthesize Vc has been reported in many ancestral vertebrate lineages, suggesting the ability for de novo synthesis is ancient.” They did not indicate how Vc synthesis arose anywhere in the paper: nothing about gain of function or transitional forms, other than this one statement: “there is an apparent transition of the organs used for the biosynthesis of Vc during evolution, from the kidney of reptiles to the liver of mammals.” However, loss of function is mentioned throughout.
“Our recent research has challenged the traditional opinion that bats cannot synthesize Vc by showing that GULO genes in two species (Rousettus leschenaultii and Hipposideros armiger) are still in their intact forms and can produce functional proteins,” they said. “Bats are perhaps in the process of large-scale loss of Vc biosynthesis ability, and show varying degrees of lack of GULO function.” From this information, they traced the lineages of bats that have Vc synthesis and those that have lost it. Assuming bats evolved from a common ancestor (which they did not specify as anything other than a fully-flying bat, but only inferred using phylogenetic software), they found a stepwise mutation pattern:
Interestingly, ancestral sequence reconstruction exhibits a stepwise mutation pattern (figure 4) that starts around the time when the tested bat species first evolved from a common ancestor around 58 mya. The ancestor of all bats maintains most of the original Laurasiatheria gene form (with only two mutations) after divergence with non-bat Laurasiatheria species; the ancestor of Hipposideridae, Rhinolophidae, and Megadermatidae (origin around 52 mya) has 3 mutations; the ancestor of Hipposideridae and Rhinolophidae (origin around 39 mya) has 4 mutations; the ancestor of Pteropodidae (origin around 23 mya) has 7 mutations; and the ancestor of the recently emerged Pteropus bats (around 3 mya) have 13 mutations, hence showing a stepwise accumulation of mutations during bat GULO evolution.
While this sequence is instructive (assuming their phylogenetic reconstructions are credible, based as they are on evolutionary dating), it does not show bats evolving into non-bats or gaining any new functions that were not already present in the putative common ancestor. Instead, it shows mutations accumulating, and the bats losing an important function that, while not vital, would certainly be beneficial.
Ancestral reconstruction clearly shows a stepwise accumulating mutation pattern during bat GULO evolution. By mapping each mutation step with the origination times of each clade (figure 4), we surprisingly found that the more ancient the species are, the less mutations they had accumulated; conversely, more recently evolved bats often accumulated many mutations, which supports our hypothesis that Vc synthesis involving GULO is gradually becoming less important in bats. The ancestral bats were therefore presumably able to biosynthesize Vc, and during evolution, GULO gene function is gradually becoming redundant.
By redundant, they mean that if bats are able to ingest Vitamin C in their diets, the GULO gene is unnecessary. Human sailors, of course, found that without citrus fruits on their ships, scurvy could be a fatal consequence. Speaking of humans, there is evidence for a human GULO gene that has been mutated into a pseudogene: “The gene encoding GULO in guinea pigs and humans has become a pseudogene,” the authors said, referring to prior research. If that gene could be restored, it might be possible to once again gain Vc synthesis function. No more Vitamin C supplements!
In the mutant lineages of bats, too, once-active GULO pseudogenes were found. “Bats showed lineage-specific gene pseudogenization including premature stop codons, insertions and deletions,” they said; in other lineages, the GULO genes were intact. They inferred that purifying selection is acting to conserve the intact genes, but partial or complete loss is in progress: “We found that strong purifying selection has shaped non-Pteropus bat pseudogenes, suggesting these bats are in early stages of loss in their ability to synthesize Vc…. Thus we infer that pseudogenization of bat GULO evolved recently.”
So while they spoke of evolution frequently, it is clear they were talking about degeneration of the bat genome through genetic entropy. “In conclusion, our study shows that bats are beginning to lose their ability to biosynthesis vitamin C and some have lost this ability in no more than 3 mya. During gene degeneration, stepwise mutation patterns are evident and these are important mechanisms leading eventually to pseudogenization.”
1. Cui J, Yuan X, Wang L, Jones G, Zhang S, 2011 Recent Loss of Vitamin C Biosynthesis Ability in Bats. PLoS ONE 6(11): e27114. doi:10.1371/journal.pone.0027114.
Anyone see evolution here? This is all downhill. Abilities that once existed are being mutated away. Where is the common ancestor of bats? Only in software that assumes it existed, because Darwin’s theory demands that each animal “emerged” from something simpler. Bats are notoriously resistant to this idea, because the oldest known fossil bat is 100% bat. Dr. Duane Gish was arguing this for decades in his debates with evolutionists, and it is still true, despite plenty of time for fossil hunters to find a mouse with half-wings trying to attain batdom.
This paper is another example confirming Dr. John Sanford’s theory of genetic entropy (see Genetic Entropy and the Mystery of the Genome). Mutations are dragging once-perfect genomes downward toward extinction. “Purifying selection” (not a creative process) weeds out the worst (usually by death), but allows many neutral or near-neutral mutations to accumulate, leading to weakened fitness. Vitamin C synthesis is a good example, because diet can compensate for the loss of the GULO gene. Wouldn’t you really rather have it, though?
Bible believers may take interest in the idea of a genetic bottleneck at the time of the Flood. The GULO gene was probably already mutating in the antediluvian world. There were only 8 inhabitants on the Ark. If they all had mutated GULO genes, then every human since would be deprived of Vitamin C synthesis. Interesting, is it not, that that is just what we observe.