> But none of this conclusively proves that cities cause schizophrenia and some argue the causal arrow actually goes round the other way. People with psychosis, the alternative explanation goes, are just more likely to end up living in poor city neighborhoods—something first labeled the ‘social drift’ hypothesis.
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> . But we know this can’t explain what we see in modern studies because time spent in the city is also associated with your future chance of developing these experiences. A recent study led by Joanne Newbury at King’s College London even found this effect in children, who have little say where they live.
The 'molecular genetic data' there refers to using schizophrenia GWAS hits to directly measure genetic schizophrenia risk and using individuals' genes to predict drift:
> Third, we investigated to what extent polygenic risk scores for schizophrenia predicted residence in deprived neighborhoods during late adulthood using the TwinGene sample (n=6796)...the association between polygenic risk for schizophrenia and neighborhood deprivation was statistically significant (R2=0.15%, P=0.002). Our findings are primarily consistent with a genetic selection interpretation where genetic liability for schizophrenia also predicts subsequent residence in socioeconomically deprived neighborhoods.
Since schizophrenia genes cause getting diagnosed with schizophrenia, and also predict living in deprived urban areas, at least some of the common causation must be people's genes.
I like Sariaslan's paper a lot, because of how overkill it is: he uses three independent methods and large datasets (one population-sized) to triangulate the same unexpected & unpopular result - it's pretty much impossible to dispute the drift hypothesis now.
As GWASes continue to identify SNPs and create powerful polygenic scores, you can expect to see more of this: parallel confirmation of long-standing behavioral genetics results.
Yes, although it is not easy, perhaps it is easier to live as a person with schizophrenia in an urban environment. Although inadequate, there are more likely to be some mental health services, and urbanites tend to encounter and tolerate a broader variety of human behaviors.
I wonder how much of this mystery is based on spurious correlation -- people with mental problems fleeing rural areas and moving to cities, other (social) factors that are more common in cities and influence the probability of developing a mental illness.