Was wondering what the survival advantage could have been and came across this paper:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917125/?tool=pubmed (full free text)
From the abstract:
"All humans are double knockouts. Humans lack the ability to synthesize vitamin C due to a mutation in L-gulono-lactone oxidase that occurred during the late Eocene, and humans have higher serum uric acid levels due to a mutation in uricase that occurred in the mid Miocene. In this paper we review the hypothesis that these mutations have in common the induction of oxidative stress that may have had prosurvival effects to enhance the effects of fructose to increase fat stores."
What do you think?
asked byDave_S_ (20436)
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on October 28, 2010
at 09:09 PM
Good question. I've heard that it was a genetic mutation that we eventually were able to adapt to with diet. The other option is that because of our self-selected diet the ability to synthesize C was not preserved because it wasn't as needed. Gary Taubes illustrates in his book Good Calories, Bad Calories that carbohydrates (sugars) serve to age us and also compete with the same molecular pathways that Vitamin C does with priority given to sugars. Therefore if you eat lots of carbohydrates you will need to consume more vitamin C to compensate for the pathways blocked with sugar and the degradation caused by excess sugar consumption. He concludes with the implication that paleolithic peoples eating their typical diet would not need as much vitamin C if the diet was lower in carbs. Most higher carb fruits and veggie seem to have lots of vitamin C. On a similar note, the Inuit traditionally consumed very little fruits and veggies and ate mostly meat and fat. They needed very little vitamin C which they were able to procure from whale blubber.
I'm grossly oversimplifying but that's the basic idea. Evolution can be a bitch.
on June 07, 2012
at 04:36 PM
Any answer would have to include why other primates, and guinea pigs, also cannot synthesise vitamin C. Monkeys can synthesise it, even ones with a high fruit diet. Certain birds also cannot synthesise it. It may be a case of random genetic drift. You can probably find an example for almost any vitamin where there is an animal (or yeast) cannot synthesise it. Of course its fun to make patterns.
on April 19, 2012
at 11:05 AM
I'm a simple, biochemically ignorant, layman.
However, I think we lost our innate ability to produce vitamin C simply because, as a species, we spent good amount of time eating "C" rich food. Why should the body waste it's time making C if plenty was already there?
I know this might seem a pretty facile way to put it. But that is what "I" think it boils down to.
The question is: How many millions of years does it take of a C rich diet to turn off the genetic manufacturing process?
And... How many millions of years of a poor C diet would it take to turn it back on? Personally, I think it cannot be turned back on as an "evolutionary" thing.
It is one thing to gradually lose a necessary ability, because it has been replaced from without. But it seems to be something completely different to attempt to regain that ability if it is existentially necessary.
It seems we're committed at this point. No going back... unless there is some freak tweak a geneticist can come up with. Ccould modern science somehow "fake-out" the genome to switch back to innate C production in less than a million years??
on October 29, 2010
at 05:05 AM
This would actually make sense, ie that a shorter version of something akin to metabolic disease may have been naturally selected for such that humans could put on some fat right before winter. Fruit during that season naturally have more fructose and that is also a good time to fatten up. They give the examples of hibernating squirrels doing something similar right before hibernation begins. Basically ,the squirrels develop something that looks like metabolic disease, getting fat and even developing fatty liver! Right before they hibernate. So could the humans tendency towards metabolic syndrome in presence of large amounts of fructose, which would have been available most during late summer have been naturally selected for?
Also interesting is the concept that vitamin C might act to ameliorate fructose activity. This would make sense as a natural control mechanism so that the metabolic syndrome would be less likely to get out of hand. Might be a case where just a bit of metabolic syndrome once per year and not going too far, might once have been an advantage for survival, even if it had some negative side effects on long term health. But of course, now we have food all year so we don't need to pack on pounds to survive. PLus the fructose is around all year in vastly greater amounts and now often without the presence of the vitamin C 'antidote' as the researchers call it. So the whole system is not only no longer advantageous but also is thrown wildly out of wack.
Interesting theory but of course, much research still needs to be done before it should be taken too seriously.
on September 27, 2013
at 02:28 AM
Humans recycle spent vitamin C quite well. (I'm not sure other animals that don't make vitamin C do this.) It makes sense that paltry dietary sources were able to keep humans vitamin C replete, thus the loss of vitamin C production was not a disadvantage. Our bodies actually don't like high levels of ascorbate, so that's probably an evolutionary pressure itself.
on September 27, 2013
at 01:45 AM
The loss of the ability to synthesize Vitamin C in humans was not "selected for" but as noted in the article referenced above, is a result of a well-known genetic mutation in humans, as well as our primate ancestors and cohorts. There is some uncertainty as to why this seemed to ultimately be advantageous or at least persisted through evolutionary time: http://www.nature.com/scitable/topicpage/the-mystery-of-vitamin-c-14167861
Side note; the fact that this genetic mutation in the primate line persists and is seen in the same gene location in all primates is profound evidence for common ancestry (ie evolution). The mutation in cavies is in a different gene location. The mutation happened long after the primate and cavy line diverged.
on August 15, 2013
at 03:47 PM
Can other primates synthesize it? If they can't, then it's because of them, and it's almost certainly because they are fruit eaters.
on August 15, 2013
at 03:47 AM
What do bats, cavies (guinea pigs), and humans all have in common?
Caves. At one or many points all three have had to hide or dwell in caves due to various geological events or their own nature. This theory needs a lot more delving, but that is one way all three have something that could radically change their inherent traits. No sunshine, or less sunshine dramatically alters creatures. Different levels of gases. Etc.
It wouldn't be the only aspect of the gene change, but it certainly is a common denominator.