Let me just add that the L-GLO is an abbreviation for L gulonolactone oxidase. Like most enzymes, it's named for its function, which is to oxidize L-gulonolactone. To claim its original function is unknown is therefore bizarre. It has a common function all across the animal kingdom.
In Darwinian theory which came first, the functional gene, or some non-functional precursor of the gene, perhaps co-opted from something else? How does one know what was co-opted from what?
Cordially,