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:….
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