50% genetic + 50% "unshared environment" is the rule of thumb for any complex trait, I assume that's what GP had in mind. Unshared env is a polite way of sayin

50% genetic + 50% "unshared environment" is the rule of thumb for any complex trait, I assume that's what GP had in mind. Unshared env is a polite way of saying noise; approximately 0% "shared env" i.e. parenting, education, etc. (There are many caveats, obviously.) You could do worse than https://en.wikipedia.org/wiki/Heritability_of_IQ#Estimates https://en.wikipedia.org/wiki/Heritability_of_IQ#Estimates as a place to start.