How did we lose the ability to make vitamin C? Well, it turns out that we do have all of the genes that are necessary for vitamin C synthesis, but one of them is broken, mutated to the point of being nonfunctional. The broken gene, known as GULO, codes for an enzyme that is responsible for a key step in the manufacture of vitamin C. Somewhere in the ancestors of primates, the GULO gene suffered a mutation, rendering it inoperable, and then random mutation continued, littering the gene with tiny errors. As if to mock the uselessness of pieces of DNA like this, scientists call them pseudogenes.
