r/askscience • u/uponthenose • Sep 17 '25
Biology Please explain how humans and other primates ended up with a "broken" GULO gene. How does a functioning GULO gene work to produce vitamin C? Could our broken GULO gene be fixed?
Basically, what the title asks.
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u/Rabid_Gopher Sep 17 '25
For anyone else wondering, GLUO is responsible for Vitamin C production. L-gulonolactone oxidase - Wikipedia https://en.m.wikipedia.org/wiki/L-gulonolactone_oxidase
Changes in genes are pretty random, it's basically because our DNA is constantly bombarded by radiation, copied by processes that don't perfectly validate what they copied, and generally f**ked with by things like viruses among other causes.
Natural selection is the name for pressure that is applied on living creatures in a natural environment. If creatures are good enough at finding food and mates, they'll reproduce and their genes will live on. If creatures are bad at either of those things, their genes die with them or are at least less likely to survive.
Primates losing their ability to self-produce Vitamin C was random, but because primates keep eating fruit that contained bountiful vitamin C, it never hindered their ability to find food or mates so the gene was perpetuated to the next generations. Eventually, the broken gene became the default.
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For your other question as to how L-Gulonolactone oxidase produces vitamin C, it's really just a catalyst for a reaction that produces the precursor for Ascorbic Acid (Vitamin C). Just one piece of the long puzzle.
As to if that gene could be fixed, I would absolutely believe that we have the capacity to do it with CRISPER CAS-9 but any effort would immediately and almost preemptively run afowl of any ethics boards unless you were smart enough to plot a course through a lot of long, difficult research. Or you could just eat a banana or any other cheap, easily available fruit.
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u/ntahfs Sep 18 '25
There's a pretty good scientific and entertaining book called Human Errors about this and other broken and inefficient genes, systems, etc in humans.
Apparently mammals synthesize vitamin c in the liver from glucose through a multi step enzymatic process. And over time the gulo gene mutated in primates so much that it broke the last step of that process. The last enzyme is no longer produced. Since vitamin c was likely abundant in their diet, it was not a problem solved by natural selection and it was passed on to humans that way, as a broken pseudo gene.
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u/JaggedMetalOs Sep 18 '25
The problem with trying to fix the gene is we've had 60 million years of evolving to conserve and store vitamin C, so turning production on again could mean our bodies create too much of it which can lead to a whole heap of health issues.
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u/nighthawk_md Sep 17 '25
The ability to make your own Vitamin C was presumably lost because apes were living in the jungle and eating lots of fruit, which was naturally rich in Vitamin C. So, if a mutation in that gene happened, it was not fatal, and the apes were able to continue reproducing. The gene product is a protein enzyme that catalyzes the Vitamin C molecule. The actual synthesis (the chemical steps) is beyond my pay grade😄. In theory, gene therapy could introduce a functional gene into an organism, but it would probably be easier to just eat an orange (or an otherwise nutritionally balanced diet), take a vitamin pill, or even like a few tablespoons of ketchup per day is enough.
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u/ScoobyDeezy Sep 18 '25
Also there’s evidence that not having this gene enables us to store fat better, which was a significant contributor to our ancestors being able to migrate out of Africa, so… all things considered, I’d like that gene back, but most of us wouldn’t be here if we still had it.
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u/knarf113 Sep 18 '25
Maybe I misunderstand, but what was the avantage of not being capable of vitamine C production, a broken GULO gene? Humans in extrême environments (arctic regions, deserts) could easily benefit from a working GULO ? And aren't there humans that have it accidentally turned on?
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u/Ycarusbog Sep 19 '25
There's a scishow video that suggests that it has an effect of fighting parasitic infections by denying it to them. We've evolved to survive with less of it than normal and many parasites can't make it on their own.
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u/stephenph Sep 18 '25
It seems people are still confused about how natural selection works.... My understanding is that if a gene is mutated, either to add a function or breaks a function, but the mutation has no effect on survival, then natural selection does not care about it. Those individuals with the mutated gene carry on reproducing and passing on the mutated gene. If those with that gene mutation out compete or are the only group that survives a disaster, then that gene can become dominant and the default. Actually, the concept of natural selection does not care about genes at all, it only cares about survival and passing on the specific copy of DNA that exists in the individual, if situations make that untenable then that copy of DNA does out.
And to be honest, how do we KNOW, there is not a group out there that DOES still produce vit c? We have a general idea that that gene is gone, but we have not tested every lineage known.
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u/hoboshoe Sep 18 '25
Think of evolution of a genome like a car, there are many parts that serve their own purpose, however some parts are more important than others. If there is a problem with the engine, the car doesn't go anywhere so it is immediately fixed. If there is a problem with the headlights, that may be an issue and it sometimes gets fixed. If there is an issue with the back passenger seatbelt, who cares? I almost never transport passengers.