I have written several times of my skepticism about supposed biological origins of mental illness. I agree some conditions, such as dementia, have physical origins, as for the most part such have been identified, even if they are often difficult to diagnose except post mortem. Still, in such cases, one can find a physical process. While, in the case of, say, schizophrenia, we are often told that we have found "the gene" or "the cause", only to find it is some correlation that does not hold up, and certainly no clear cut causative mechanism. I am open to the possibility that, in some cases, what we currently cannot physically diagnose may be found later to have a biological cause, but, for the most part, I believe much of what we call mental illness is, for lack of a better description, behavioral, or learned, and not physical. (The fact that so many of the diagnostic criteria are so subjective, such as "inappropriate sadness" or "excessive reaction", makes me more skeptical, but I explained that in "Mental Illness" and "The Problem With Mental Health Laws", so I will not repeat myself.)
What I want to clarify is something that many misinterpret from my premise. To say that mental ills are learned, or are behaviors, is not identical to dismissing all sufferers as malingerers, as play actors and the like. Nor is it to say such ailments are wholly imaginary, or treatments ineffective. A learned behavior may be quite distressing and harmful, and can lead to consequences quite beyond the control of the one suffering.
Let us take an extreme example to demonstrate this. Imagine an individual who was never taught to speak. Raised in isolation, without speaking or hearing speech, it is unlikely he would ever learn to speak, or even to really understand the speech of others. This would be a terrible impediment, a devastating incapacity, and yet not something biological. However, even though it is a learned behavior, or rather a lack of learning, that would not mean the sufferer was faking anything, or could easily remedy the problem.
And that is how I think of much of mental illness. Essentially, and please don't get offended before I complete this thought, it is the extreme end of the spectrum of bad habits. Now, I know many may find that offensive, but allow me to explain. Bad habits are something very specific, bits of poor socialization, and, more significantly, poor socialization we find difficult to overcome. And, in many ways, that describes a lot of mental illness, inappropriate, or uncomfortable reactions to events that the sufferer finds difficult or impossible to suppress. Obviously, this is not a full description, but it covers a lot of the topic, and it demonstrates how we can understand non-biological mental ills. Rather than bad brain chemistry or something similar, is it not possible that some or all arise from inappropriate socialization? I know many see this as blaming parents, but that is not the case either. Learning on the part of children is not a process entirely controlled by parents, the child himself has some role, as do a host of environmental factors, many in ways complicated enough that they are almost impossible to understand. Thus, it is perfectly plausible that a parent, though doing nothing wrong, could have a child whose combined internal thoughts, environment and upbringing interact in such a way as to lead to this sort of improper response.
Similarly, it is not a surprise that chemical intervention is beneficial to some patients. After all, we have been "curing" normal mood problems with alcohol and drugs for a long time. Is it any surprise other chemicals may also be beneficial? Even those which do not produce euphoria, or stimulate or depress, can have a beneficial effect. After all, brain chemistry clearly can effect mood. (Then again, what are thoughts but brain chemistry?) So, one does not need to postulate a biological source for mental illness to accept that medication may help.
I know I am in a minority here, and I accept that. I am also open to counter arguments. But at present, I have not seen anything that strikes me as convincing proof of a biological origin, while there is much in my experience that inclines me to see mental illness as a combination of socialization, simple excesses of emotion, and -- in some cases -- fraud*. And that ignores completely the final category, which I find many find even more uncomfortable, those who behave in ways we find disconcerting or strange, and thus dub mentally ill, but who seem perfectly content with their own lives. Granted, at one time this included a much larger number of people -- promiscuous daughters during more reserved ages, shiftless sons during the same, interracial couples at one time, dissidents in a number of more authoritarian states, and so on -- but there are still many who are dubbed ill who have no bigger problem than behaving in peculiar ways. Which is yet another reason I find the whole topic of mental illness being a true disease so troubling, behaviors which would be acceptable in some other place and time are dubbed an ailment here and now, in other words, it is the only disease I know which is diagnosed entirely by context. That seems suspect to me.
* I am reluctant to write this, as some will see this one line and forget everything else i said, but face it, some people fake mental illness. As a onetime worker in social services -- especially as one determining eligibility for benefits -- whose ex-wife worked at a mental hospital which housed a number of criminals, it just seems self evident some percentage of those dubbed mentally ill are acting, either to avoid jail or continue welfare benefits. (And that does not even cover the large number of mentally retarded who were relabeled mentally ill because one diagnosis had more funding than the other.) Sorry, but it is true, whether or not we wish to admit it.