Scott Alexander has a post up that is getting a lot of attention, Non-Cognitive Skills For Educational Attainment Suggest Benefits Of Mental Illness GenesNon-Cognitive Skills For Educational Attainment Suggest Benefits Of Mental Illness Genes. Scott concludes:
But the big shock here is schizophrenia. As of last time I checked, the leading hypothesis was that schizophrenia genes were just really bad, evolutionary detritus that we hadn’t quite managed to weed out. And although they definitely decrease IQ, they seem to be good in other ways. Not with certainty: the correction for false discovery rate kills a lot of the effect (though this is the question I would have been most interested in before reading these results, so maybe I can ignore that?). But there’s at least a faint signal here.
I’ve actually heard from psychometricians that there is a weird signal in relation to the genetic correlation between schizophrenia and various outcomes which are not all negative. One model for schizophrenia you might have is that it’s totally bad. But, another model might be that it’s “good actually” in small dosages or in some genetic backgrounds, but bad in other cases. The argument can be generalized to many “mental illnesses.”
The issue more broadly is that the genetic architecture of mental/behavioral traits is complex, and often subject to a normal distribution. Is this simply mutation-selection balance? Or is there balancing selection? There is now evidence that markers associated with homosexual behavior boost fertility when present in individuals who are not gay. This could be a simple way that these alleles remain in the population at a given frequency (assume frequency dependence). As we understand the genetics of schizophrenia and autism, and begin to screen embryos, I think these questions will become more relevant.
Greg Cochran still thinks it’s detritus:
https://westhunt.wordpress.com/2018/07/22/more-theory/
Cochran has also argued, if I understand correctly, that recessive genes among the Ashkenazim which lead to severe, typically fatal disorders for the homozygous heighten the intelligence of the heterozygous. Is there any reason to think something similar might be true with respect to non-cognitive skills for some genes that can cause schizophrenia? That for some of these genes, having one copy may enhance non-cognitive skills but having 2 copies results in a higher probability of schizophrenia?
Speaking of markers associated with homosexual behavior, I’ve seen the argument made that the exceptionally low concordance of homosexuality in identical twins (if I recall, around 40%; I assume this means that given one homosexual identical twin, the odds that the other one is also homosexual are around 40%?) suggests that genes with a direct pro-homosexuality effect probably don’t exist. Genetic associations with homosexuality would then be restricted to things like genetic associations with languages spoken, which are quite strong at the same time that the genes are not actually related to the phenotype, or things like genetic drives toward behaviors which end up promoting homosexuality for some external reason.
I’d be curious about your view.
marcel proust: Cochran’s “overclocking” hypothesis is that there was intense selection for something like five centuries on Ashkenazi Jews as they formed a new community in a new environment (for them). Over a longer period of time, such risky mutations would tend to be replaced by better ones.
Michael Watts: I thought the concordance rate was significantly lower than that.
Both of my grandfathers were highly intelligent and achieved men. One, an engineer, the other, an aviator. Neither of my parents are particularly bright; my mother’s a dullard who barely scraped through a biochem degree, and my father’s a polisci grad who worked in military intelligence. Between both sets of grandparents, there are six children in my parents’ generation. Though my mother’s two brothers seemingly inherited her father’s intelligence, both are shattered men with profound psychiatric issues, primarily low motivation and paranoia. My father’s sister and brother are evidently no higher than 110, and neither of them are particularly noteworthy by any measurement of ability.
In spite of his own mediocrity, my father was very successful in his career. He’s relatively fastidious in his work, very motivated and focused. His head is very bizarrely small, to a degree which is visibly apparent. There are so many indications, from his observably languid processing speed to his poor academic mathematical performance in youth, low recreational literacy, and lack of curiosity, that he is not any more intelligent than his siblings. Without his personality traits, the positive trajectory of his career and his finances would be difficult to explain.
In both my parents’ cases, I think they were poisoned by my grandmothers. My mother’s mother was an irritable, paranoid and domineering personality who was always easily outmaneuvered. My father’s mother had such intensely crippling postpartum depression that she was institutionalized in an era where such a thing was a socially stigmatized last resort. Postpartum is frequently comorbid with other disorders that are correlated in the linked study with lower IQ. However, in my father’s case there may have been a silver lining- his father did not have OCD nor demonstrate any irregular anxiety. It is implied that my father may have inherited OCD from his mother. The results of this contamination have allowed him to salvage a moderate generational loss of intelligence. He’s the only child of six across two families whose patriarchs were exceptionally intelligent that has seen any financial, occupational or academic success.
@Michael Watts
I’m pretty sure the genetic variants referenced in the article that Razib linked are ones associated with high r2d4d, a proxy measurement for prenatal testosterone sensitivity which has a positive correlation with homosexuality and transsexuality in men. Women with high r2d4d’s are more fertile than ones with low (“masculine”) digit ratios. Digit ratios have been proven to have a strong heritable component. There’s some adage about good mothers making bad (effeminate, yielding, gay) sons and good fathers making bad (masculine, aggressive, lesbian) daughters. Steve Hsu posted about this a while back.
Anecdotally, I’ve heard from friends who lived through all-male schooling abroad, including in a few places where historical pederasty was common, that hierarchies with a sexual component are often formed within these environments based on a mix of seniority and perceptions of femininity or masculinity. There are probably a lot more opportunistically homosexual men, both pitchers and catchers. I would assume that a fair few “obligate” homosexuals are extreme manifestations of such a phenomenon. Probably somewhere between that and a paraphilia.