> The usual analogy is that you can always lower the IQ of a child by hitting them on the head with a hammer or by lacing their food with lead powder. But no intervention has been found that raises IQ.

Since almost no one, without deliberate intervention, experiences an environment completely free of known factors that are detrimental to IQ compared to the optimum environment, it's purely a semantic game to say that there are no known interventions that increase IQ.

I read recently of two identical twins separated at birth with on growing up in South Korea and the other in the United States, the twin who grew up in SK had an IQ 15 points higher than her identical sister. The connections in the brain either degrade or strength depending on how it's used and I can absolutely see a person's IQ being increased by engaging in subjects/tasks adjacent to what most IQ tests measure.

The study you reference: https://www.gwern.net/docs/genetics/heritable/adoption/2022-...

The South Korean twin had an IQ of 100 (Slightly below average for her country) and the US twin had an IQ of 84. (Significantly below average)

So, still no evidence of an intervention that can increase IQ, but plenty of evidence that it can be lowered.

Yep. Note the US twin was literally whacked on the head, and that's probably why this MZA pair is so very unusual (and popularized, unlike other MZA reports like the authors' prior one, incidentally) and breaks away from the usual MZA correlation of ~.8.