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