IQ and identical twins

Monozygotic (identical) twins raised apart are more similar in IQ (74%) than dizygotic (fraternal) twins raised together (60%) and much more than parent-children pairs (42%); half-siblings (31%); adoptive siblings (29%-34%); virtual twins, or similarly aged but unrelated children raised together (28%); adoptive parent-child pairs (19%) and cousins (15%). Nothing but genes can explain this hierarchy.