What Twins Show

Identical twins start with the same DNA down to the last letter. Raised apart, they often stun researchers with shared habits, tastes, and personality quirks they could never have copied from each other.

Yet they are never carbon copies. Those gaps are the fingerprint of environment at work, shaping two different people from one identical blueprint.

The Minnesota Twin Study tracked dozens of identical twins separated as babies and reunited as adults. Their IQ scores tracked closely, correlating at about 0.75 on a scale where 1.0 would mean a perfect match.

Close, but not a copy. The rest of the difference came from the separate lives each twin actually lived.