I noticed the exchange about the genetics of schiz: lots of confusion. My take is that current data suggests that most schiz iz the result of mutational pressure: possible because it is really many different syndromes lumped together – a grab-bag. The number of loci that can mutate in a way that causes something in that grab-bag is very large. When people do find causal variants, they tend to be rare, generally specific to a particular (and shrinking) family. Average lifetime of an allele of strong effect is something like three generations.
That said, environmental factors can surely contribute. There is a real but small seasonal pattern, and a real but strong influence of prenatal starvation. The Dutch famine of 1944 and the Chinese famine associated with the Great Leap Forward each roughly doubled schizophrenia in those in-utero at the time. Then again, it’s higher in big cities than in rural areas. 2.4 times more common in Copenhagen than on a Danish farm.
Selection pressure against schiz is fairly strong today and was likely stronger in the past: people too crazy to farm or hunt generally starved, along with their children.
Creativity may well be more stronger in unaffected relatives, but I doubt that creativity boosted fitness much in most past environments. While having long conversations with little silver men living behind the wallpaper was in general quite bad for fitness.
gcochran commented the LW discussion on the blog: