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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?

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Dave, interesting article. Seems to make sense. Evolution only cares for good health as long as it enhances reproduction. Of course we value health very much. – Pieter D Oct 29 2010 at 6:59
So, maybe obesity is caused by fructose that has no Vitamin C? HFCS/sucrose alone is bad, but fructose in fruit is okay? – Dave S. Oct 29 2010 at 19:08
@Dave S. I think your on to something :) Watch out bricks can get thrown through your windows for saying such a thing. – Edward J. Edmonds Aug 5 2011 at 15:56

4 Answers

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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.

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 I guess my point is that the loss of uricase and Vit C synthesis MUST confer a survival advantage or we would not ALL have that mutation. I had read that the loss of uricase leads to slight rise in blood pressure due to elevated uric acid - which we would have needed to be able to stand erect without passing out. But this mutation came much earlier, so it helped us later, but there must have been some survival advantage previously - which this paper speculates about. – Dave S. Oct 29 2010 at 11:44
I forget if it was Taubes in GCBC or William Dufty in Sugar Blues, but I read somewhere that while vitamin D was found to cure scurvy in sailors on long voyages (hence the nickname "limeys" for British sailors), sailors who didn't consume as many refined carbohydrates (in the form of biscuits & crackers) didn't get scurvy in the first place. Whatever the mechanism (and thanks for the good explanation, Levi), it does seem that the more carbs you eat, the more vit C you need to take. (Prob refined grain carbs...I can't see fruit/tubers interfering all that much, when they have C themselves.) – Amy B. Jun 7 at 20:03
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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??

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That would explain why some people lost the ability, if it just weren't necessary. But to be a total knock-out indicates that it confers some survival advantage. Otherwise, there should still be some genetic remnant of it - if it were survival neutral. In other words, people did better due to a lack of ability to manufacture vitamin C. (Assuming that my limited understanding of how evolution works is correct.) – Dave S. Apr 19 2012 at 12:26
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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.

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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.

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