Is there a world - real or imagined - where having diabetes would be advantageous to one’s survival? If diabetes isn’t new why has type I and II persisted for so long? Was there an evolutionary advantage in being diabetic. Are there mammals that exist without the use of insulin or an insulin-like hormone?
A little rambling:
I am thinking if there was an evolved mechanism to break down glucose to pyruvate extracellularly it might work. Though that means that mitochondria would have be extracellular too. It seems to me that body’s use of transporters to pump glucose into the cell is too cumbersome. Why bother bringing in the pump when it can just leave it outside the cell?
I feel required to point out that it needn’t be an advantage, only not a disadvantage in surviving long enough to reproduce. Also, certain triggering situations like obesity might not have been present in sufficient numbers earlier in our evolution to set off the problem to enough of an extent to create a disadvantage.
Although diabetes per se may not confer any survival advantage, the metabolic conditions which predispose to type II diabetes could be expected to.
In brief …
If a person is resistant to insulin in his muscles (or more resistant there relative to any degree of resistance elsewhere in the body), the following might occur:
During times of starvation (often associated with a need to migrate to search for food and thus increased muscle energy demand), the muscle will be “unlikely” to take up a glucose molecule due to muscle insulin resistance. So, the glucose is spared to be used by the brain (which otherwise must use ketones of nothing!). OTOH, FFA’s from the lipolysis of stored triglyceride, will fuel the muscles much more efficiently than glucose (this last fact is independent of muscle insulin resistance).
During conditions of feeding, when glucose levels tend to be rising, insulin levels will go very high since glucose will have difficulty getting into muscle (the primary and major destination for glucose) due to insulin resistance there and thus accumulate in the circulation. In this situation of high insulin levels and relatively normal adipose tissue sensitivity to insulin, energy will be preferentially stored there. Over the long term this will lead to markedly increased fat stores (if there’s lots of food), i.e. obesity. Likewise, the increased demand on the beta cells to make more insulin (to overcome the resistance), will promote their “exhaustion”.
Hence, from #2, during times of starvation, there will be a large adipose mass that can be used for energy until food is available.
This is a nice system for environments where food is scarce. When food is plenty, the insulin resistance etc., culminate in beta cell exhaustion and diabetes.
I meant to give one good link, at least. The thinking I summarized was called the “thrifty genotype hypothesis”, so you can search on that term, but note that that phrase doesn’t mean the same to everyone.
Very interesting. But still, I wonder why they didn’t think this mechanism is more apt for the pathogenesis of type II DM (yes, I know it’s cold in Scandinavia and that’s where type I is quite common …). As well, type I DM is autoimmune in nature and is often an ‘all or none’ disease. I don’t see how “occult” type I DM could exist (at least for more than a few months anyway for most people so afflicted). Moreover, type I DM is clearly linked with other autoimmune diseases such as thyroiditis, adrenalitis, etc., suggesting it is part of a bigger picture and not just a means to confer protection against ice crystals.
That is very interesting but wouldn’t the individual still have to deal with the fatal affects of high blood glucose? If you freeze someone are glucose molecules expended? Even so, I am not convinced that someone with high glucose would be afforded protection from frostbite that would ravage epithelial tissue.
If you were to list things that were the biggest threats to one’s survival to reproductive age, diabetes would be waaaaaay down the list. Individuals who lived long enough to reproduce (survival), passed their genes on. The fact that the genes got passed on answers the question. Diabetes did not significantly affect enough of the population in such a way as to prevent them from reproducing. If it did, we would be having this thread.
If you were to list things that were the biggest threats to one’s survival to reproductive age, diabetes would be waaaaaay down the list. Individuals who lived long enough to reproduce (survival), passed their genes on. The fact that the genes got passed on answers the question. Diabetes did not significantly affect enough of the population in such a way as to prevent them from reproducing. If it did, we would not be having this thread. :smack:
But I’ll repeat: the genes which give a tendency to the development of diabetes may well have conferred an evolutionary advantage, and thus were passed on by many individuals. Hence, the “high” rate of diabetes we are seeing.
One of the current theories on the cause of diabetes is that it’s the result of an overactive immune system, killing off a virus that diabetics are genetically predisposed to, which attaches itself to the Islet of Langerhans on the surface of the pancreas. The immune system kills off the virus, then, just to make sure, kills off the Islets, too. The Islets are what release insulin into the bloodstream… so, in order to save itself from a virus that had little to no effect, the immune system kills off a critical organ… So, a self-destructively strong immune system could be added to the list of possible benefits (aside from the diabetes, I hardly ever get sick).
I can see no reason to believe that passing on diabetic genes would be increasing, and it is not even proven this is happening, and if so, it tends to skip generations, so there is much to learn. As to the increase in diabetes, yes, this is true, but it is more likely due to diets, or lack of good ones. In addition, all the processed foods and so called fast foods we now have are all contributing factors, so I would think the increase is not due to changing genetics.
Also, keep in mind that many risk factors for Type II Diabetes, obesity and high glucose, simply weren’t an issue until the Industrial Revolution. People who had the luxury of eating high-sugar, high-fat foods undoubtedly had their genes sought after.
I disagree. One example of why I disagree can be found in the famous story of the peppered moths of Industrial England. Originally, nearly all these moths were light coloured, an advantage given the white birch forests they lived in. As the Industrial Revolution accelerated, and as soot was produced in larger and large quantities, the birch trees’ bark darkened. Over a 50 year period, the percentage of dark moths went from essentially zero to 95% (since being dark, and hence less visible to predating birds, conferred a survival advantage).
The trait for dark colour clearly does not represent something that many, most, and certainly not all, peppered moths possesed originally. Its frequency in the population grew.
As pollution and soot diminished, so too did the frequency of dark moths. The cycle was complete.