Theories of Everything
Chemistry, which is sometimes referred to as "applied physics" (usually by physicists), has quantum chemistry, which is a close approach to a "theory of everything" in that field.
Biology (which snide chemists refer to as "applied rudimentary chemistry") has yet to develop anything even remotely resembling a "theory of everything". This is due to the immense complexity of the systems involved (so say the biologists) or the immense simplicity of the biologists involved (so say the chemists and physicists), take your pick.
However, I have noticed that at least one small segment of the biological sciences seems to be developing a "theory of everything". In fact, it seems to have developed several.
I refer, of course, to the field of autism "alternative" research.
The Grandmother of Grand Unified Theories of Autism
The first truly successful (in the sense of "popular" rather than "accurate") candidate for the "Grand Unified Theory of Autism" has to be the "mercury-causes-autism" hypothesis, first published (in Medical Hypotheses) by Bernard et al in April 2001. This hypothesis asserted that autism and mercury poisoning were one and the same, based on the use of similar words (in English) to describe certain features of both disorders.
Despite the fact that none of the authors had actually seen, let alone diagnosed a person with actual mercury poisoning, this hypothesis resonated with the zeitgeist of the community of parents with autistic children and resulted in massive popular support. Its scientific support has been less massive, unfortunately, and it stands in peril of fading to a mere cult phenomenon.
As a "theory of everything" in autism, the mercury hypothesis has met most of the requisite criteria. It is flexible enough to "explain" the features of autism, even as the definition of autism continues to change. In part, this is due to the protean nature of mercury poisoning, which has a wide variety of symptoms and signs.
However, a large part of the credit goes to the flexibility of the people applying the mercury-causes-autism hypothesis, who are willing to overlook significant ways in which autism differs from mercury poisoning. It is this willingness to suspend critical thinking, more than any inherent validity of the hypothesis, that accounts for its continued survival despite its lack of supporting data and the vast amounts of direct and indirect data refuting it.
With only a vague and easily disputed connection between signs and symptoms of autism and mercury poisoning and a few unrelated (and some might say also trivial and obvious) studies to support it, the mercury-causes-autism hypothesis is in trouble. The few studies that have been held up in support of the hypothesis, on closer examination, do not support it.
Some of these studies merely confirm what is already known (trivial), e.g. that mercury is neurotoxic. Others have shown that mercury can cause other types of disorders, e.g. autoimmunity, without connecting that to autism. In the end, most of the studies used to support the hypothesis are of three basic types:
 The study fails to show a connection to autism - i.e. mercury causes X, X is a bad thing, but no indication that either X causes autism or that X is part of autism, with X being a sign or symptom.
Example: Hornig, et al, "Neurotoxic effects of postnatal thimerosal are mouse strain dependent". This study demonstrated that mouse strains that were known to be prone to develop autoimmune disorders were more likely than other strains (which were not prone to develop autoimmune disorders) to develop autoimmune disorders after exposure to thimerosal. This is the trivial part of the study.
They then go on to posit that a variety of behavioral responses of the mice - decreased movement and decreased reaction to novelty - were signs of mouse autism. This is more than a bit of a stretch, as there are several alternative explanations, including the simple explanation that the mice were not feeling well, having developed autoimmune disorders.
 The study shows association without data supporting causation - i.e. the sudy shows that X is found in children with autism, but fails to show that X might cause autism. X might be caused by autism or simply be a co-traveler.
Example: James, et al, "Metabolic biomarkers of increased oxidative stress and impaired methylation capacity in children with autism", which demonstrates signs of increased oxidative stress in autistic children without showing that the oxidative stress led to autism or what the cause might be. Significantly, when they corrected the signs of oxidative stress with betaine and folinic acid, the children remained autistic.
 The study proposes mechanisms that are either unsupported by the data and/or are contrary to known physiology
Examples: Kern, et al, "Sulfhydryl-reactive metals in autism", and Holmes, et al, "Reduced levels of mercury in first baby haircuts of autistic children". Both of these studies found reduced levels of mercury in the hair of autistic children and both propose - without providing a single citation or shred of data to support the proposal - that autistic children excrete less mercury into their hair.
This is contrary to decades of research into hair physiology, and so should have been accompanied by at least a paragraph of explanation. However, neither group of authors have found it necessary to provide support for their astounding claim that hair excretes mercury. Until they can, both studies are merely sources for scientific amusement.
The mercury-causes-autism hypothesis also has no explanation for the continued rise in autism numbers (from data sources that its proponents used to establish the "autism epidemic" in the first place) despite falling mercury exposure (both in vaccines and from the environment) and so its supporters have resorted to circular reasoning.
Despite having failed to establish that mercury causes autism, the proponents have boldly claimed that trace amounts of mercury remaining in vaccines, along with environmental mercury (which has been dropping since the 1960's), are sustaining the rise in autism.
This, of course, completely negates their earlier assertions that it was the rise in vaccination - and exposure to thimerosal - that caused the rise in autism, since the mercury exposure to children born after 2000 has been less than that of children born before 1980 (before the onset of the "autism epidemic").
What they have done - or tried to do - is say that the continued rise of autism (in USDE and California CDDS numbers) supports the mercury-causes-autism hypothesis because of the continued exposure to mercury - this continued exposure being proven by the continued rise in autism. And so, even though it took mercury exposures far in excess of what children are presently receiving to start the "autism epidemic", it takes only trace amounts to sustain it. Anyone want to go around again?
Another tactic used in support of the mercury-causes-autism hypothesis is to claim that chelation "cures" (or treats, if you like) autism. This supposedly establishes that mercury is the cause of autism, although it conveniently overlooks the fact that the chelating agents - if they do work - have effects beyond removing mercury.
Even more fundamentally, the proponents of the modified mercury-causes-autism-because-chelation-cures-autism have failed to support their claim that chelation has an effect on autism that is greater than placebo. Until this is established, they have no argument. They are trying to "prove" one unproven statement with another unproven statement.
Other "Theories of Everything" in Autism
Other "theories of everything" have arisen in the field of "alternative" autism research since the rise of the mercury-causes-autism hypothesis, although none have generated as much press or excitement. What these lesser hypotheses share with the mercury-causes-autism hypothesis is an emphasis on anecdote, unrelated (to autism) studies and hype.
Some of the current contenders for the "theory of everything" are:
 Nitric Oxide - since this is a widespread inter- and intra-cellular signalling molecule, it is not surpising that it is found in association with a variety of disease states. It is also not surprising that it is affected in a variety of conditions, both normal and pathological. This is roughly equivalent to saying that calcium is associated with autism, since calcium fluxes are critical in release of many neurotransmitters, including those thought to be important in autism.
Unless nitric oxide can be shown to either cause or treat autism, it remains just an interesting footnote. Considering the amount of hype that nitric oxide has in the "alternative" medicine and "nutraceutical" fields, it is no surprise that it has found its way into "alternative" autism therapy.
 Allergens (especially latex) - what could be more ubiquitous than latex? It's in car tyres, surgical gloves and a myriad of medical, industrial and household products. Latex allergies are on the rise - probably due to increased exposure, although this can be debated - and so is autism. Coincidence? Almost certainly, but this hasn't stopped some people from seeing a connection. It's not their fault - finding connections is what our brains are "hardwired" to do - even when there isn't a connection.
 RF energy (from cellphones, of course) - this seems to be a revival of the old "cellphones cause brain tumors" urban legend and should be as readily dismissed. Yes, the use of cellphones has paralleled the rise in autism. So has use of the Internet, popularity of Britney Spears and numbers of hybrid automobiles.
Doubtless, there are many others that I have overlooked. Feel free to e-mail me your favorite "theory of everything" for autism.