From Synthesis to Dependence:

Buried inside our genome right now are molecular fossils, bits of DNA that are so broken that they no longer work. Over 90% of our genome doesn’t code for anything. And embedded in all this non-coding DNA, like bones in rock, are fossilized pseudogenes.

Pseudogenes are sequences that were once active, but are now basically dead, with a few rare exceptions.

Around 20,000 of them are found in our genome. One of these can be found on our 8th chromosome and it’s called GULOP. It used to do something pretty important for our early primate ancestors. It gave them the ability to make their own vitamin C. But that all ended around 61 million years ago in the middle of the Paleocene Epoch when something happened in the DNA of one of those early primates. The gene effectively died, becoming a ‘pseudogene,’ a non-functional molecular fossil.

Now our more distant primate cousins on the other major branch of our family tree, like the lemurs, can still make their own vitamin C. Ever since the death of GULOP, our side of the primate family tree, (the tarsiers, monkeys, and apes) have had to get vitamin C from the food we eat, this includes fruits and vegetables such as oranges, strawberries, kiwis, broccoli, bell peppers, and leafy greens. In some cases, vitamin C supplements may be recommended under the guidance of a healthcare professional. Without that vitamin in our diets, the immune system may be weakened, increasing the risk of illnesses, frequent infections, delayed wound healing and risk suffering from diseases like scurvy.

How did GULOP die?

Well, the short answer is mutations. Mutations occur randomly in our DNA all the time. They’re totally normal and a source of new variation, and variation is the raw material for evolution. Occasionally, mutations occur at particular spots in a gene that inactivate it, which prevents the instructions it carries from being translated into a protein. That’s what happened to GULOP millions of years ago. A mutation inactivated it, turning off its ability to make an enzyme called L-gulonolactone oxidase, which is responsible for the final step in the synthesis of vitamin C. Without that enzyme, our ancestors couldn’t produce the vitamin.

In evolution, if a mutation that inactivates a gene reduces fitness, or the ability of an organism to survive and reproduce, natural selection will get rid of it by selecting against the individuals that carry the mutation. This process keeps useful genes free of mutations. But the loss of GULOP probably didn’t reduce the fitness of our ancestors. When it became inactive our early ancestors were likely already getting a lot of vitamin C from eating fruits. This resource was becoming more abundant as tropical forests expanded throughout the Paleocene and fruiting plants continued to diversify. Then the mutation spreads throughout the population. This happened either through a random process called genetic drift, or through natural selection. Eventually, the mutated gene became ‘fixed,’ meaning it is the only version of that gene left in our gene pool.

Reviving GULOP.

Reviving a pseudogene like GOLUP, would require significant genetic manipulation and modifications. This could potentially involve gene editing techniques to repair or replace the non-functional segments of the gene. But the revival of GULOP would not be a guarantee that we would regain the ability to produce our own vitamin C. Hopefully the understanding of genetics with the help of artificial intelligence we would be able to revive pseudogenes in the future.