In summary, we report heritability estimates that are consistent with those of previous studies and support substantial genetic contribution to phenotypic IQ; around 40% of the variance can be attributable to it. With regard to the environmental contribution, shared environment accounts for 50% of the variance, and non-shared environment accounts for the remaining 10%.Those figures are consistant with everything else I've read.
Yes, so about 60% of IQ is from non heritable factors, that is, the majority of it.
There is as much variability in IQ within a single family as there is between racial groups.
And that 60% difference is the difference between coming home to an empty house and a Nintendo and coming home to parents who want to know why you got a B on your test and what you are going to do to make an A next time.