Why did we lose the ability to produce vitamin C?

[AdGULO]

Hi,
I am always interested in the question as to why we lost the ability to produce vitamin C? Genetic studies have shown that humans, as well as other scurvy-prone mammals, was able to synthesize vitamin C endogously at one point, but lost this ability 25 million year ago. My question is that if vitamin C is essential for survival, what evolutionary advantages does it confer in losing this ability? And why had natural selection favoured (or maybe not) this loss? I mean, if we had not lost this ability, we would not have had to rely on vitamin C pills at all. I hope my arguement is logical.
AdGULO

[Dolev]

Very logical argument. If someone less lazy than myself doesn't answer you soon, I'll do it.

[Van Carman]

An interesting point is the primitive monkeys,such as lemurs have the intact GLO.Higher monkeys ,apes chimpanzees and homo sapiens do not..I thank God for the discovery of ascorbic acid and that it is widely available and inexpensive.It is not a vitamin but an essential body metabolite.I know others can add much more good information.Sincerely,Van

[ofonorow]

We were created in God's image but perhaps not a perfect replica..

or, our brain size allowed us to survive in poor health where other less intelligent creatures died off

or, have you ever seen Jurassic Park and do you understand the reason for the aptly named "lysine contigency" to control the dinosaurs?

or, we don't know.

Pauling explained that during the course of evolution, the advantage of not having to produce something available in food results in a reduction in the net energy required favoring the cells that can dispense with making the substance.

We do know that very few species are alive today who can't synthesize ascorbate.

We don't know

[AdGULO]

Hi,
I absolutely agree with you that we do NOT know the answer. But we don't need to know the answer to formulate a hypothesis or even plain speculation. After all, it is the first step to come to understand a phenomenon.
AdGULO

[DanSco]

One theory is that the evolutionary advantage is the starvation advantage. A relatively large amount of glucose is used up to produce ascorbate. One can easily imagine the scenario where an ascorbate producer remains very healthy early on, but dies of starvation before the springtime comes. Also easy to imagine is the otherwise identical genetic mutant that uses no glucose for ascorbate, who is with scurvy but alive in the spring.

It is also said that domesticated animals produce less ascorbate than wild animals. People that raise animals would naturally like the animals that grew faster and larger and needed less food. If the reason that they grew faster and larger and needed less food was because they produced less ascorbate, then that trait would be inadvertantly selected for by breeding.

[zucic]

One theory is that the evolutionary advantage is
the starvation advantage. A relatively large amount of glucose is
used up to produce ascorbate.

This argument has one weak point: even today, millions of years later,
three enzymes are still working, using some glucose in a process which
failes to end properly!

[DanSco]

One theory is that the evolutionary advantage is
the starvation advantage. A relatively large amount of glucose is
used up to produce ascorbate.

This argument has one weak point: even today, millions of years later,
three enzymes are still working, using some glucose in a process which
failes to end properly!

Mutations are not always neat and tidy, and it's not something I'm going to argue about!

[Dolev]

The products of those 3 enzymes probably have some other benefit, or they also would have mutated away, I guess.

Anyway, AdGULO, to expand on what Owen mentioned above, there must have been a time when "living was easy" (to quote Janis Joplin), and there was plenty of ascorbic acid available from the food supply and the environment was healthy. During these conditions, the energy needed to produce the ascorbic acid was wasteful. I've seen estimates that from 1/2 -4% of energy from food is used by mammals to make AA, so when the GULO gene mutated, this was an evolutionary advantage.

Experiments have been done with bacteria which give strong support for this idea. For example, bacteria unable to produce tryptophan due to a mutation were put half and half with bacteria who could produce tryptophan. When the solution did not contain tryptophan, of course the mutants died off. However, when the solution contained adequate tryptophan, the mutants took over completely in about 50 generations.

[ascorbicjoe]

Some feel that humans and those animals equally afflicted with this genetic defect were just mistakes that were masked by living in a vitamin C rich environment.

I am leaning to a theory that some side effect of tameness leads to lower C levels and eventually a turning off of the system in some extreme cases. I thought that is was strange that most domesticated animals have low C levels. When Russian researchers were trying to tame the fox for their fur industry the foxes became more doglike as they tamed. Droopy ears, multicolored coats and puppy like behavior expressed. They noticed that adrenal output dropped and likely changed how the dogs genes worked. I tried to find the current researcher on this project to ask about V-C levels, but I doubt they were checking for it.

I ask, "Did we tame ourselves?" It is apparent that tameness is a trait humans like in all pets and domesticated farm animals. Did we first seek this tameness in our own species? Many of our livestock were herd/pack animals. Even, Guinea Pigs are domesticated from herding rodents! These animals needed to be more relaxed with their own kind. They needed to work with others to survive. Many animals will kill others of their own species on sight. We have gone to the extreme, we are willing to risk meeting strange members of our species on a routine basis. We are VERY tame.

It could just be a mistake, but there could have been a reason we lost our enzyme. It may have been in an effort to lower our adrenal output to maximize our ability to negotiate with our neighbors instead of wasting effort in combat.

However, evolution does make clear that animals do not invest more than they need in an activity. Nature wants a return on investment. The leads me to conclude that ascorbic acid levels in animals, even the highest levels may be a compromise. More may be somewhat better, but possibly not worth it when it takes valuable resources from more important processes. That means that we may use more V-C than animals produce. We have the benefit of mass producing ascorbic acid with out the expense of generating it within our bodies. Other species may be a guide, but we need to keep an open mind.

[zucic]

The products of those 3 enzymes probably have some other benefit, or they also would have mutated away, I guess.

I have done some search and found these interesting things:
(1) The compound called UDP-glucuronic acid is used by liver
to perfom detoxification.
(2) The same compound is an intermediate in ascorbate synthesis.
(3) UDP is still made by our livers.
(4) The first GULO gene mutation, which wreched the gene, occured a
long time ago, yet the remaining three enzymes are still working.

Here is a simple theory:
- There was a plenty of ascorbate in a diet of our ancestor, but some
environmental disaster forced these creatures to include some foods
which were ignored before. The same disaster maybe even caused
the mutation.
- Mutation spared small fraction of glucose, but large fraction of
UDP-glucuronic acid for detoxification.
- Significantly improved detoxification was an obvious advantage,
while the loss of ascorbate synthesis was not very significant, because
the newly introduced foods also contained ascorbate.

[Bobber]

Dr. Zucic,
Do the animals which still synthisize AA also produce less UDP-glucuronic acid?

[zucic]

Dr. Zucic,
Do the animals which still synthisize AA also produce less UDP-glucuronic acid?

No. If intermediate products are used for more than one purpose,
there is more left for other purposes if ascorbate synthesis is lost.

[Van Carman]

Go in on this interesting article,via search engine.I hope to hear comments and explanations of what this means.Thank you ,Van

[trillian]

One potential element to consider in the evolutionary 'success' of an animal is its lifespan.
There is a balance between the time for each generation and the longevity of individuals
being advantageous or not. Many animals die relatively young because their lifestyle is so
demanding. If the time between generations is shorter then genetic changes can take
place sooner and only the fittest will influence the gene pool.

Gorillas live to about 35 in the wild and about 50 in captivity (chimps live a bit longer sometimes).
So we humans are probably now living about twice our evolutionary optimum age. In other words
if we had not intervened in so many ways and extended our lifespans by the use of technology etc.
we would probably live to similar ages as Gorillas or Chimpanzees if we were in the wild as
hunter-gatherers.

In the context of a 35-40 year lifespan many illnesses will not yet become a big factor so if the
loss of ascorbate synthesis was a short-term advantage and was compensated for enough by
the diet at the time then it is easy to see why the downside was not a problem initally.