If you define interventions only as things that a single individual could change while living in the current system, then that's true yeah. But that's usually not what people mean when they discuss policy and the fact that heritability is specific to certain environs
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Nations adding iodine to table salt on increasing population level intelligence (through reducing deficiencies causing intellectual delays) is a great example of this.
Any large RCTs on iodine in water treatment in Africa? My prior on these claims is very negative these days. E.g., recently, I read those 1960s civil rights reports and these cite massive experiments on social policies, busing and similar, stuff, all negative and uncited today.
