Social contact and sibling similarity: facts, issues, and red herrings.

We consider evidence that shared experience is associated with sibling resemblance and report new analyses of our earlier data to assess the magnitude and meaning of that association. We cite recent Swedish studies of early separated twins and present new data from reared-apart twins in Finland. Results of these analyses confirm our earlier conclusion that, for some dimensions of personality and life-style, twins who cohabit longer into adulthood and twins who retain closer contact after separation are more alike. Further, new analyses here reported are consistent with our earlier inference that, for neuroticism and consumption of alcohol, cotwin differences in contact precede, and causally contribute to, differences in behavioral similarity.