Do environmental similarities explain the similarity in intelligence of identical twins reared apart?

Abstract

Taylor (1980) claims to show that the similarity in IQ between monozygotic twins reared apart (MZA's) in the three classic studies by Newman, Freeman, and Holzinger (1937), Shields (1962), and Juel-Nielsen (1965) is due to similarity in their environments. A reanalysis, using Taylor's classification of the twins into similar and dissimilar environments on the basis of four different criteria, but using the alternate IQ measure used in two of the studies, shows that his findings do not constructively replicate. Taylor's conclusion that "it seems reasonable to suggest that the IQ correlations characterizing pairs of individuals with absolutely identical genes and absolutely uncorrelated environments would be extremely low" cannot be substantiated from the evidence at hand.