ELI5: how is it possible that different kinds of animals (including humans) have lost the ability to produce vitamin c independently?
ELI5: how is it possible that different kinds of animals (including humans) have lost the ability to produce vitamin c independently?
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It is easier to get certain nutrients from nature. Humans can’t make all the proteins its bodies needs, but other animals and some plants do make those proteins. So we just eat them.
It is like a rich person. They could work for a living, but they could also use their money to buy assets, like apartments, and rent them out to people who can’t afford to buy their own, making money without producing anything.
There’s a phenomenon called “convergent evolution” where different species, often very distantly related, will independently evolve very similar traits. Good examples include the flippers in whales, fish, and penguins or the wings on birds, bats, and insects.
Unless you meant specific to vitamin C. In that case, it’s an example of evolutionary loss happening once a selective pressure has been removed. If dietary sources of vitamin C are abundant and easy to obtain, then the inability to produce vitamin C endogenously ceases to be a disadvantage and therefore ceases to be selected against by natural selection. This allows inactivating mutations within the vitamin C biosynthesis pathway to accumulate in the population over time until they become so common that few or no individuals are capable of synthesizing vitamin C anymore.
All it takes is a single mutation in the GULO gene to render that gene, which codes for the production of L-Gulonolactone oxidase, non-functional. Loss of a functional L-Gulonolactone oxidase enzyme means the pathway for making vitamin C is broken. As for why specific, different species got this non-functional gene, we don’t know, but multiple independent evolutionary origins are not uncommon. For example, eyes evolved independently several times.
In species that lost the ability to make vitamin C and are still around, that loss wasn’t an evolutionary disadvantage because they got more than enough vitamin C from their diets anyway, so the non-functional gene has no effect. For example, primatesn (including humans and our evolutionary ancestors) have plenty of fruits and vegetables in our natural diets that give us all the vitamin C we need.
Vitamin C is so abundant in fruits and some veggies that even though we developed a negative mutation that caused us to lose the ability to make our own, it didn’t impact us because we got enough from the food we ate.