On Wed, 23 Feb 2000, Madeline Stratton wrote:

> My
> own personal theory as to why we have so much mental illness now, is that
> 100,00 years ago, someone as sick as I was would not have survived long
> enough to pass on such defective genes.

Maddy, I suspect it may be more complicated than "defective"
genes.  Most genes are pleiotropic, which means that they are
linked to more than a single trait.  This can create a situation
where a given gene is expressed in one trait that is "good" and
another that is "bad", certain percentages of the time.  The
classic example is the gene that confers to resistance to malaria
in those who are heterozygous but results in sickle cell anemia
in those who are homozygous.

I believe that the genes that predispose people to mental
disorders such as depression may increase in frequency because
they are also linked to favorable characteristics.  It is
possible that those favorable characteristics are increasingly
important in modern society, and so rates of depression also
increase, as the genetic "cost" of the desirable traits.

A case in point is autism.  There has been some research
indicating that autistic children are more likely to be born in
families where parents or close relatives are techno-geeks:
engineers, programmers, mathematicians, i.e., people whose work
involves lots of intense and sustained formal reasoning.  Such
skills are at a premium in recent decades, and at the same time
autism rates are climbing.  I wouldn't call this a proof of
anything, but it is something to think about.

Todd Moody