My subjective impression from the correlation studies that I have seen is that the remainder largely is a long list of purely negative factors - i.e. in the "nu

My subjective impression from the correlation studies that I have seen is that the remainder largely is a long list of purely negative factors - i.e. in the "nurture" stage there are many ways to screw up the development of children with a large impact, but limited ways to meaningfully improve it over the genetic 'baseline'. I.e. the correlation of nutrition in IQ is mostly driven by malnutrition, not by differences between great nutrition and mediocre nutrition; the impact of parenting is heavily driven by the outlier cases of severe abuse or deprivation, not the differences between great parenting and mediocre parenting, the impact of peer groups is largely set by the minority of cases that result in severe addiction or gang membership, not the difference between lousy friends and great friends, etc - that's the pattern that I seem to see there.