Anyway, to balance out the evilness of the "Marijuana causes Schizophrenia" pearl-clutchers, I am going to go ahead and quote my favorite parts of Robert Sapolsky's speech because I know you people are too lazy to read the whole thing. Here goes nothing:
One of the keys about schizophrenia is that it's a disorder with a genetic component. That doesn't mean it is genetically guaranteed. It is not genetically determined. There is a genetic risk for this disease, as is the case with most psychiatric disorders.
The minute you see there's any genetics on the scene, you've got to ask an evolutionary question, which is: "Where did these genes evolve from?" Why do we have schizophrenia in every culture on this planet? From an evolutionary perspective, schizophrenia is not a cool thing to have.
What's evolution about? Evolution is the process by which adaptive traits become more common. Schizophrenia is not an adaptive trait. You can show this formally: schizophrenics have a lower rate of leaving copies of their genes in the next generation than unaffected siblings. By the rules, by the economics of evolution, this is a maladaptive trait. Yet, it chugs along at a one to two percent rate in every culture on this planet.
So what's the adaptive advantage of schizophrenia? It has to do with a classic truism--this business that sometimes you have a genetic trait which in the full-blown version is a disaster, but the partial version is good news.
What's the example we all learned in the textbook case? Sickle-cell anemia: full-blown version, fatal hematological disorder; partial version, you don't get malaria. Tay Sachs disease: full-blown version, your nervous system is destroyed within a couple of months of life; partial version, you're resistant to tuberculosis. Cystic fibrosis: full-blown version, you're typically dead by 20; partial version, you're resistant to cholera. This turns out to be a theme with a lot of human genetics. As long as there's enough folks with the advantageous partial version, you can afford the occasional cousin with the full-blown version.
Evidence suggests this is what the genetics of schizophrenia is about. What's the partial version? It's the disease that got identified about 30 years ago. The first study that found genetic evidence for schizophrenics looked at about 20,000 people adopted in Denmark, looking at patterns of inheritability of schizophrenia; were you likely to share schizophrenic traits with your adopted parents, or your biological parents?
This was a massive multi-year study. Psychiatrists talked to more relatives of schizophrenics than any psychiatrists had ever done before in a career. What they noticed was, there's something kind of weird about relatives of schizophrenics--not every single one of them, but at higher than expected rates. This "kinda weirdness" is now called "schizotypal personality."
What is schizotypal? It's a more subtle version of schizophrenia. This is not somebody who's completely socially crippled; they're just solitary, detached: these are the lighthouse keepers, the projectionists in the movie theaters. These are not people who are thought-disordered to the point of being completely nonfunctional; these are people who just believe in kinda strange stuff. They are into their Star Trek conventions. They're into their astrology, they're into their telepathy and their paranormal beliefs, they're into--and you can see now where I'm heading [laughter]--very, very literal, concrete interpretations of religious events.
Schizophrenics have a whole lot of trouble telling the level of abstraction of a story. They're always biased in the direction of interpreting things more concretely than is actually the case. You would take a schizopohrenic and say, "Okay, what do apples, bananas and oranges have in common?" and they would say, "They all are multi-syllabic words." [laughter] You say "Well, that's true. Do they have anything else in common?" and they say, "Yes, they actually all contain letters that form closed loops." [laughter] This is not seeing the trees instead of the forest, this is seeing the bark on the trees, this very concreteness.
What you find with schizotypals is what is called metamagical thinking, a very strong interest in new-age beliefs, science fiction, fantasy, religion, but in a very concrete, literal form, a very fundamentalist style. Somebody walking on water is not a metaphor. Somebody rising from the dead is not a metaphor; this is reported, literal fact.
Now we have to ask our evolutionary question: "Who are the schizotypals throughout 99% of human history?" And in the 1930s, decades before the word "schizotypal" even existed, anthropologists already had the answer.
It's the shamans. It's the medicine men. It's the medicine women. It's the witch doctors. In the 1930s an anthropologist named Paul Radin first described it as "shamans being half mad," shamans being "healed madmen." This fits exactly. It's the shamans who are moving separate from everyone else, living alone, who talk with the dead, who speak in tongues, who go out with the full moon and turn into a hyena overnight, and that sort of stuff. It's the shamans who have all this metamagical thinking. When you look at traditional human society, they all have shamans. What's very clear, though, is they all have a limit on the number of shamans. That is this classic sort of balanced selection of evolution. There is a need for this subtype--but not too many.
Sorry it's such a long quote but I am very fascinated by genetics, evolution and everything that makes humanity such a fascinating species of mammal. I get such joy out of discovering what makes us tick and where we really come from. I sometimes think I should study science and biology if I grow up.
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