[doubleunplussed]

I think most in the rationality community (and otherwise in the know) would not say that IQ differences are almost entirely biological - I think they'd say they're about half genetic and half environmental, but that the environmental component is hard to pin to "parenting" or anything else specific. "Non-shared environment" is the usual term.

They'd agree it's largely stable over life, after whatever childhood environmental experiences shape that "non-shared environment" bit.

This is the current state of knowledge in the field as far as I know - IQ is about half genetic, and fairly immutable after adulthood. I think you'll find the current state of the field supports this.