[colechristensen]

>Evolution isn’t stupid

Evolution also isn't smart. Have so much of something in your diet and you'll tend to lose the ability to manufacture it because there's little evolutionary pressure to maintain it. If you're a VitaminCless mutant you don't die and your children survive just fine and suddenly this becomes common in the species.

It didn't get lost because it was advantageous for it to be gone, it just wasn't important enough to get maintained.