Nathan Lents: Why Human Have Such a Needy Diet

Excellent article on human diet. Any comments from YECs or IDs and anyone else? For me personally, I am almost always Vit D deficient. Even though I try to get as much sunshine as possible in the summer months, I need to take supplements to stay within the normal range especially in wintertime in Northeast US.

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From the same article:

Our ancestors stopped making vitamin C because they suffered a mutation in their GULO gene. This was tolerated because they already had vitamin C in their diet. Our ancestors stopped absorbing bacteria-produced vitamin B12 in their large intestine, because scavenging was providing dietary B12 in their small intestine. And so on.

I remember reading, years back, about vitamin C synthesis, and how we, as humans, once possessed this capability. I understand the mutation process described above, but two things have always bothered me about the narrative:

  1. How in the world would something like this ever spread to the entire population of humans? I believe that it was early humans, not some progenitor, who were known to have this functionality. So, are they suggesting that the entire population “suffered a mutation in their” shared “GULO gene” or possibly that it was manifest through some horrific bottleneck in which the vitamin C producers were wiped out and only the non-producers survived?
  2. There always seems to be a personification of mutation / selection in these discussions, wherein evolution occurred and it was “tolerated” because there was vitamin C from other sources, or scavenging provided another source of B12. Why does any of that matter? It was seemingly caused by a mutation in a gene within a protein. Why go on and explain why the modified organism was so happy to accept that change? It’s happiness or willingness or tolerance has nothing to do with it, the way I see it.
  3. If there is some connection between evolutionary changes and benefit/tolerance/happiness and the organism, why in the world would we expect something like vitamin C synthesis, which could do so much to avoid free radical and heavy metal damage, to go away? It seems to run contrary to the evolutionary expectation that evolution begets improvement. (I’ve heard of vitamin C synthesis being too costly, but we’re talking about major benefits with it vs. without it.)

Maybe you can explain this to me @Patrick .

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I think it was the common ancestors to all humans - a species of monkey where the ability was lost tens of millions of years ago. From article: Unfortunately, an ancestor of all primates lost this ability many millions of years ago and primates have been dependent on dietary vitamin C ever since.

Perhaps these are great questions to ask Dr. Nathan Lents. Paging Dr. Lents …

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This is a great one for Nathan to give a shot. Send him a note, and see if he answers.

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I sent him a request on twitter, hopefully he will stop by.

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Thanks to you both! This is really great. I’ve honestly wondered about this for ten or more years. I hope that we hear from him!

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I see… I thought I recalled reading elsewhere, many years back, that it was a human trait and that humans had lost it. I remember thinking that there could be a parallel in the Bible where God limits the years of human life to around 120 years. With free radical damage seeming to cause so much of our aging (inability to recover), it seemed that having a virtually endless supply of antioxidant would have been quite handy…

The short answer is genetic drift. The inactivation of GULO had no deleterious effect because that fateful primate ancestor already had vitamin C in its diet. It had no advantage, either, so its fixation in that ancestor population was pure bad luck. Genetic drift events, where an allele is fixed in the population by pure chance, seem unlikely but are really common on long time scales. In fact, many of the genetic markers and haplotypes used to study human populations are the result of genetic drift.

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Same. I am slightly low in vitamin D, although less so in summer months. Honestly, I’m not entirely sure what to make of it. I do pop the supplements, though. Vitamin D seems to have a great many benefits. I’ve published a couple papers on it.

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@Patrick was (almost) right when he said the ancestor of all primates lost the ability to synthesise vitamin C (through the breaking of the the GULO gene). The GULO gene became a pseudogene in the common ancestor of the Haplorrhini - the so-called “higher primates”. The other major clade of primates, the Strepsirrhini have the gene intact.

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What further proves the point is that GULO mutations have also popped up in a couple other places. Guinea Pigs and Fruit bats, for example. Because their diet already provided plenty of vitamin C, there was no consequence and genetic drift fixed the mutation. However, as expected, the mutations are different in each of these separate events. This underscores how all creatures are being bombarded mutations all over the place. The multiple times that lactase persistence has emerged in human also makes this point.

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Thanks very much for responding so quickly! This is a very interesting topic.

My first question was how that mutation got fixed in a population.

Is there a simple explanation as to how this mutation became fixed in a population? It does seem unlikely, as you say above. I try to picture in my mind how one organism or animal is affected by this mutation and next how that becomes translated to the entire population. I cannot ever quite figure out how that occurs. With malaria and resistance, it is easier to see, but with larger organisms with smaller populations and much larger gestation cycles, it really boggles the mind.

This really pertains to my second question. I don’t understand why the narrative so often contains discussion around the effect (or non-effect) of a mutation. It seems as though one is to understand that either the organism or evolution itself is supposed to care about whether it benefitted or not.

It had no deleterious effect, it had no advantage, it was pure bad luck. Why even mention this? I’m not being silly, here, I’m trying to understand the rhetoric. Are you suggesting that, as with the guinea pigs and fruit bats, above, if their diets didn’t provide enough vitamin C they would have somehow rejected the mutation or otherwise mutated?

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Thanks!! So, did modern man ever have it or can we know? I understand that we can see the genetic remnant of the capacity to synthesize vitamin C, but can we know if man were ever able to do so?

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Seeing as humans never had a functioning GULO gene, apparently we have never been able to synthesise our own vitamin C.

Yes, an individual born with a non-functional GULO gene would quickly die or be extremely sickly if their diet didn’t contain any vitamin C - they wouldn’t produce any offspring so the trait would die out. In other words, the ancestral primate population would have had to have a diet rich in vitamin C for the first “breaking” mutation in GULO to be tolerated in that individual. After several mutations build up in the GULO gene, including large deletions of chunks of sequence, all of the descendents of this population would have been stuck requiring vitamin C in their diets.

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The normal range is not enough to get clear of cancer risk. Take enough supplements to get above 50ng per ML. The medical limit is 30ng per Ml. I can show you evidence this is not enough if you like :smile:

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So the GULO gene mutation was after the Haplorrhini - Strepsirrhini split? How long ago was that? So every descendant of the Haplorrhini branch has the mutant GULO? This is interesting because one of its decedents didn’t realize that they had a broken gene until they started taking long ocean voyages abroad British navy ships and developed scurvy.

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About 74 million years ago, according to timetree.

As far as I know.

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I was at 25ng per ml last winter. Doctor prescribed 5000 IU of Vitamin D per day and now my level is 65 ng per ml. No magic, no prayers, just medical science and technology having a positive impact on people lives.

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Okay, thanks very much. I understand this now and because of how you explained it, I now think I understand why Dr. Lents was emphasizing each organism’s reaction or response to the mutation. He was explaining how it may have become fixed in that population (because the fruit bat consumed fruit that contained vitamin C, the mutation was not so deleterious that the animal did not die. Subsequently, the population in which that mutation became fixed also consumed vitamin C, and so were not affected.)

Now that I understand the purpose, the italicized aspect of the narrative below seems really unnecessary.

If there is a mutation, and it has a deleterious effect on an organism, the organism dies. So isn’t is implicit in the process that mutations that are fixed are either neutral or beneficial anyhow? Isn’t that really a description of the evolutionary process anyhow?

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