Fifty-plus pairs of identical twins were raised apart with no formative contact.

Evidence

In addition, they have located from around the world over fifty pairs of identical twins reared apart. … While the members of these monozygotic twins raised apart (MZ-apart twins) would probably not have been raised in starkly different environments, the researchers determined that most of them had been separated soon after birth. … None of them had contact during their formative years, and most of them had no contact for most of their lives. — Bob Altemeyer, The Authoritarian Specter, 886