Main article: Evolutionary perspective on chronic disease
The mainstream, but antiquated, view about chronic disease is best expressed by a certain physician thusly: “Of our thousand bacterial species, I only have to worry about a couple dozen” while a 2002 Nature paper concludes, “Multicellular organisms live, by and large, harmoniously with microbes.1)
However, there is substantial evidence that chronic diseases are caused by pathogens as opposed to other causes. This evidence includes:
In addition, it seems highly likely that supposedly non-infectious chronic diseases are in fact caused by pathogens when one considers their clinical features, histology, treatment response, microbe populations, presence of co-infections, the ease with which co-infections proliferate, and the failure of systematic lifestyle interventions.
According to the Marshall PathogenesisA description for how chronic inflammatory diseases originate and develop., humans accumulate a plethora of pathogenic bacteria during their lifetimes, and it is the genetic mutations which result from active infection that play a major role in what is commonly thought of as “genetic susceptibility.”
Besides the absence of proof implicating human genes as the major causative factor, there is a range of evidence - including strong epidemiological and compelling evolutionary evidence - suggesting that pathogens cause chronic diseases.
Epidemiological evidence including case clustering in time or location supports a pathogenic cause for disease.
There is also the following types of evidence, the first three of which are noted in a 1998 article and 200527) paper by David Relman and David Fredricks:
Main article: Evolutionary perspective on chronic disease
One useful way to determine if a disease is caused by faulty human genes is look towards the central principle of evolutionary biology: evolutionary fitness. Evolutionary fitness is defined as the extent to which an organism is adapted to or able to produce offspring in a particular environment. The fitness concept can be applied to the problem of disease causation to distinguish evolutionarily feasible hypotheses of causation from marginally feasible or untenable ones.52) 53)
If the common inflammatory diseases (including autoimmune diseases) were genetic, the only way they would manage not to be weeded out of the population would be if they conferred some sort of beneficial survival trait not related to the disease.
To date, no such benefits have been identified in any chronic disease, schizophrenia being a good example.54) Schizophrenics have a high suicide rate, few children, and a high rate of abnormality in their children.55) 56) Schizophrenic mothers are more likely than non-schizophrenics to have stillborn babies and children with congenital malformations.57) This would mean schizophrenic mothers and fathers would be less likely to pass on a theoretical schizophrenic gene to their offspring. On the contrary, incidence of the disease is only escalating suggesting that bacteria are passed from generation to generation.
Biology and law typically don't have much in common, but one useful metaphor for considering the validity of a proposed pathogenesis for chronic disease is to compare the search for the cause of disease to that of a trial for homicide. Two key pieces of evidence in any such trial are opportunity and motive. Basically, could the defendant have done it, and was it in his interests to do so?
Bacteria have both motive and opportunity.
Unlike toxins, environmental causes, human genetics or many of the other major proposed causes for chronic disease, bacteria are driven by a biological imperative, namely the evolutionary impetus to promote their genes through aggressive reproduction. Of course, the same cannot be said for other potential causes, especially human genes. In fact, it's decidedly in the interests of humans not to pass on genes, which limit reproductive fitness, in some cases drastically so.
<html><!– The Vitamin D ReceptorA nuclear receptor located throughout the body that plays a key role in the innate immune response. (VDRThe Vitamin D Receptor. A nuclear receptor located throughout the body that plays a key role in the innate immune response.) is at the heart of innate immunityThe body's first line of defense against intracellular and other pathogens. According to the Marshall Pathogenesis the innate immune system becomes disabled as patients develop chronic disease. and transcribes thousands of genes.58) Given that the VDR can be inactivated by ligands bacteria are known to create and the fact that 90% of cells in the human body are bacterial, bacteria certainly have the opportunity to cause disease as well.
Some, as a matter of principle, take issue with the MP's “one size fits all” explanation of the pathogenesis of disease. Not to mix metaphors, but bacteria's ability to subvert the VDR is the equivalent of a widespread and easy-to-exploit flaw in a widely distributed operating system for computers. The VDR is evidently quite powerful, by one count coding for over 27,000 human genes59). So, it's not as if humans can evolve itself an alternative in the near term.
Versatile thought it is, the VDR has an enormous vulnerability, one which every species of pathogenic bacteria can take advantage. Can and do software bugs happen on an equivalent scale to that of chronic disease? Absolutely. With scarce resources, why would a group of bacteria engineer an alternate “exploit” if this method for facilitating survival has been working so well for millenia? –></html>