Are heart disease, cancer and schizophrenia caused by pathogens?

June 10, 2002 5:45 PM

Are heart disease, cancer and schizophrenia caused by pathogens? The logic basically goes that a genetic disease cannot have a very high rate of occurrence as natural selection would prevent that gene from surviving (leaving the few occurrences of the disease that are caused by random mutation). Also: how to make diseases more benign by altering the parameters to their natural selection.
posted by fvw (19 comments total)

via maudlin's link to ESR's blog.
posted by fvw at 5:50 PM on June 10, 2002

Interesting how homosexuality is briefly mentioned but no further evidence or reasons for this hypothesis are given. (I can't imagine what a virus would have to gain by making people be attracted to unsuitable mates, nor do I see how it could be a side-effect of something that is in the pathogens best interest)
posted by fvw at 5:51 PM on June 10, 2002

The logic is stupid. None of those diseases don't stop you from reproducing. Most don't even really affect you until after reproducing age. Not to mention the DNA only makes you 'more susceptible', its not a guaranty.

Evolution is all about 'good enough', not 'perfict'
posted by delmoi at 5:52 PM on June 10, 2002

Wow, I can't belive ESR wrote so much about porn. That man is an idiot.
posted by delmoi at 6:07 PM on June 10, 2002

delmoi: Read the article. They mention why even diseases that hit you after reproducing might be bad...
Evolution is _not_ about good enough at all, it's about best.

delmoi: Wrong thread. (and with criticism like that, wrong site)

Does raise an interesting point however: as it is only recently people live long enough to suffer the consequences of heart disease, cancer etc, maybe the evolution away from it will only start now....
posted by fvw at 6:16 PM on June 10, 2002

I can't imagine what a virus would have to gain by making people be attracted to unsuitable mates

Unsuitable mates? My mate is quite suitable, thank you very much.
posted by evanizer at 6:17 PM on June 10, 2002

Help me on this one. Does this mean that smoking doesn't cause lung disease of bad hearts or cancer. Only diseases do?
posted by Postroad at 6:58 PM on June 10, 2002

If we cannot track them to some hostile environmental element (including lifestyle), Ewald argues, then we must look elsewhere for the explanation.

elementary!

"When diseases have been present in human populations for many generations and still have a substantial negative impact on people's fitness," he says, "they are likely to have infectious causes."

but then yeah, like delmoi said, he kinda takes a leap of faith there :)

not that it shouldn't be investigated, and no doubt pathology is a useful heuristic :) it's just that making bold claims to advance your cause (esp. now!) might be counterproductive.

also i was just thinking if like cancer and other intractable diseases and stuff are caused by pathogens, then it might be like malaria and sickle cell anemia, where the disease is actually an evolutionary defense mechanism or autoimmune response or something.
posted by kliuless at 7:26 PM on June 10, 2002

They mention why even diseases that hit you after reproducing might be bad...

Yeah, but the thinking behind the explanation if flawed. For instance to paraphrase they say Grandmothers tend to gather food, so even diseases that hit at 60 may have some negative impact on gene survival.

Except that life expectancy even a handful of generations ago (pdf) wouldn't have been anywhere close to 60, and those grandmothers would have been closer to 40 years old.
posted by willnot at 7:36 PM on June 10, 2002

Help me on this one. Does this mean that smoking doesn't cause lung disease of bad hearts or cancer. Only diseases do?

Many diseases like cancer and heart disease have multifactorial causes. Take peptic ulcer disease, for example. Until fairly recently, physicians thought ulcers were brought on by too much acid in the gut, or some breakdown in the tissue layers that protect us from the erosive effects of that acid. Some ulcers, however, are caused by chronic infection with Helicobacter pylori, and ulcer patients are cured by a combination of antibiotics. However, this does not mean that all ulcers have an infectious etiology.

Similarly, there is no doubt that bacterial infection can cause horrendous heart disease. Streptococcal infections can cause serious valvular disease. But even in older populations, physicians have been suspicious at some of the changes they see in atherosclerotic lesions, because they look similar to what one sees with inflammation (goddamn that word!) and the body's response to infection. Studies have indicated there might be some correlation between chronic infection with Chlamydia pneumoniae and the development of atherosclerosis. I imagine, however, that taking a two week course of antibiotics is not ever going to be the whole answer to ischemic heart disease: smoking and cholesterol appear to be wholly capable of inducing undesirable changes in coronary arteries even without hide-nor-hair of an infectious agent.

Some cancers (eg some types of leukemias) have been shown to be associated with viral infections, and it may be that other cancers will be shown to have an association with infection. I think the thing to keep in mind is that typically a number of cellular insults or "hits" are required to create an immortalized cancer cell. In simplified terms, to turn any given cell into a cancer cell we might have to induce DNA damage that turns off the cells programmed apoptosis, knock out its own tumor suppressor machinery, cranks up its basilar membrane invading capabilities, etc. Someone who smokes, drinks too much, is exposed to environmental industrial carcinogens, has a genetic predisposition, and so forth, increases his or her risk of cancer. Perhaps an exposure to an infectious agent also constitutes a cellular transforming "hit" in some instances.
posted by fold_and_mutilate at 7:37 PM on June 10, 2002

fvw: Evolution is _not_ about good enough at all, it's about best.


If that were true, why would so many people need glasses? Wouldn't the myopic gene have been weeded out by now? Is fatness caused by pathogens too?

(Of course, you might claim myopia was caused by an infection). While there might be some truth (or a lot) to this idea of chronic disease being caused by pathogens, the idea that it applies to all of them is a pit moronic. The article mentions that grandmothers are still useful for society, but forgets that in the 'pre-industrial' era people had kids in their teens. Hardly anyone lived long enough to be affected by Alzheimer's.

Also, if a disease took only a 1% hit, it would take 77 generations for it to accumulate a 50% loss of population. It would take another 77 generations to get down to 75% of a population loss, etc. Sure it might 'eventually' go down to 1 in 100,000. But it would take a long time. Sadly, my ti89 is in my car, otherwise I could tell you how long.

I think we should explore all possibilities for curing these kinds of diseases, but making sweeping generalizations about things is dumb.

(also, there was a link to ESRs blog, which features the sex story. I didn't realize there was already a mefi thread about that)
posted by delmoi at 7:38 PM on June 10, 2002

Fascinating post. I'm still adjusting to the new Unified Theory of Ulcers, so I'd certainly be willing to give these people research time and money to explore the theory.

Dismissing a fairly complex technical or scientific theory that has some support from well-credentialed folk in the appropriate community as “stupid logic” based on a cursory reading suggests a limited ability to consider new information. The tendency to react immediately with a two-second binary opinion rather than reflect and perhaps even research before responding seems to be encouraged by the medium, but still.

Scientific progress requires the development and discussion of new and strange-sounding hypotheses, and to jump on a new idea as a leap of faith misses the point. If it turns out that they can't find causation, they'll lose funding and have problems in peer review—that's how it works.

And finally...a front-page post can hardly go into the details of a complex scientific development, and as such, I found this one no more sweeping than it needed to be.

Complaint over now. It's been building up as I see post after post on tricky scientific and medical issues casually and frequently ignorantly judged and dismissed with a flick of the mouse.
posted by blissbat at 8:26 PM on June 10, 2002

postroad: Help me on this one. Does this mean that smoking doesn't cause lung disease of bad hearts or cancer. Only diseases do?

no, it merely means (or at least might mean) that those illnesses you named are caused by your environment, not your genes. Wether it's the tar and nicotine you inhale or the viruses partying in your veins it doesn't say anything about.

delmoi: fvw: Evolution is _not_ about good enough at all, it's about best.

If that were true, why would so many people need glasses? Wouldn't the myopic gene have been weeded out by now?

Easy answer: So many people now can get glasses so it's not a (significant) weakness anymore. :)

more to the point answer: Myopic gene? I have yet to see evidence that myopia is genetic, though some tests have indeed shown some genetic correlation, which suggest some genetic makeups give people who are more susceptible to the pathogen or environmental factor. Given enough time, and if its worth the energy to create a guaranteed working eye, evolution will create one. However, it's probably more efficient to risk the diminished eyesight and not expend lots of energy on the creating of perfect, everything-proof eyes.
posted by fvw at 8:53 PM on June 10, 2002

The tendency to react immediately with a two-second binary opinion rather than reflect and perhaps even research before responding seems to be encouraged by the medium, but still.

Best. Criticism. Ever.
posted by rushmc at 9:11 PM on June 10, 2002

However, it's probably more efficient to risk the diminished eyesight and not expend lots of energy on the creating of perfect, everything-proof eyes.

Plus the fact that most erosion of vision in pre-modern society probably occurred after breeding had been successfully accomplished.
posted by rushmc at 9:13 PM on June 10, 2002

rushmc: Plus the fact that most erosion of vision in pre-modern society probably occurred after breeding had been successfully accomplished.
The article does actually mention that even after breeding has been accomplished fitness is still useful as it increases the chances of offspring.. I have my doubts about how much this matters after a certain point, but it's got to count for something...
posted by fvw at 9:40 PM on June 10, 2002

None of those diseases don't stop you from reproducing.

Thats a double-negative so your saying all of the diseases stop you from reproducing. Either way you are incorrect. The world is not so easily defined in black and white. Did you read the article or just the FPP?
posted by stbalbach at 6:45 AM on June 11, 2002

delmoi - If that were true, why would so many people need glasses? Wouldn't the myopic gene have been weeded out by now? Is fatness caused by pathogens too?


I believe I've read that vision problems are much less prevalent in pre-literate societies. In other words, there's a strong environmental link due to the change in how we use our eyes. As far as fat, historically that's a survival trait, not a evolutionary weakness. Throughout most of human history, food has been limited and physical labor has been hard, so the ability to store fuel is a vital tool for survival. It's only very recently that the possibility of practically unlimited food for a population doing little physical exercise has been conceivable. Ewald is not arguing for germ theory in cases where we have clear environmental causes.

The argument regarding the shorter lifespans of the past is stronger, but remember that charts showing average life expectancy in the past are misleading. The high child mortality rate greatly skews those numbers. If you survived to adulthood, you had a decent chance of continuing to survive to the age where cancer or heart disease might be a factor.

A different argument against this theory as it applies to certain diseases is the evolutionary trade-off between the survivability in youth and in old age. The physiologic complexities of devlopment involve a myriad of engineering trade-offs. Perhaps a gene that improved chances of surviving as a child might also increase susceptibility to cancer at age 60. In this case, the survival of the child wins out over the survival of the 60 year old. (This is the current prevailing logic for evolutionary explanations of inevitable aging & death.)

I am very interested in the possibility of this theory with regards to mental illness. Schizophrenia, depression, et al, are not diseases of old age, so the evolutionary argument is much stronger.

The suggestion regarding homosexuality is intriguing on the intellectual level, but given that homosexuality is not a harmful condition for the person involved, I wouldn't put it high up on the list of research needs. Evanizer - your mate may be quite suitable from the human standpoint of having a happy, healthy relationship with someone who loves you. From the standpoint of your genes, who don't give a damn (metaphorically) if you are happy or not, your mate is a disaster. The interests of our genes are not the same as our best interests.

fvw - great link!
posted by tdismukes at 7:49 AM on June 11, 2002

The article does actually mention that even after breeding has been accomplished fitness is still useful as it increases the chances of offspring.. I have my doubts about how much this matters after a certain point, but it's got to count for something...

Yeah, I started to add that caveat but decided that I think the relevance is probably small enough that it would be simpler just to eliminate it from the discussion. :)
posted by rushmc at 11:39 AM on June 11, 2002