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Comment by lambdaphagy | Hacker News Reader

"Upbringing" can be a slightly misleading way of stating that summary, as most people think of upbringing as comprising environmental factors that parents can influence. But factors that parents can influence should be largely shared between siblings, and studies typically find that the effect of shared environment is quite small in adulthood. IQ researchers typically find that 60-80% of the variance in IQ is explained by genetics, and most of the remainder to "non-shared environment", a grab bag of factors not shared between siblings that we might as well call "luck".

The above is a slight simplification, but I think it's a fair summary of the current consensus among intelligence researchers, given the word count.

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If I remember correctly, the last time I looked into this, there was some doubt about the validity of many of the twin and sibling based IQ studies, because the parents who consented tended to be wealthier.

The upshot was that genetics is probably more of an upper limit on IQ, and that for children raised in poor conditions, environment plays a much bigger role than genetics.

Restriction of range is a potential concern, but not all studies are subject to that criticism. Bruce Sacerdote's study of Korean adoptees randomly assigned to American families found, for example, that the adoptive families represented perhaps the middle 90% of the SES spectrum. Obviously you will rarely see children adopted into the lowest percentile, but you can compare children taken from the lowest percentile to children who are raised natively in that percentile, and you typically find small or nil differences for most outcome measures in adulthood.

Plenty, of smart, dedicated people have been trying for decades to devise interventions to permanently boost IQ among children raised in poor (for the first world) conditions, and unfortunately not much has turned up. Instead, there is a familiar pattern of small pilot studies that show initial promise, but whose gains tend to wash out when the program scales up to a less than one-to-one child/child psychologist ratio, or even when the children are followed up on in adulthood.

The gains from permanently boosting IQ among low-IQ children would be so great that it might still be worth banging our heads against that wall on the off chance that we find something that might work. But we should keep in mind the base success rate of past interventions.

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