EFFECTS OF EARLY REARING ENVIRONMENT ON TWIN SIMILARITY IN THE LAST HALF OF THE LIFE-SPAN

In the Swedish Adoption/Twin Study on Aging (SATSA), 99 identical and 229 fraternal pairs of reared-apart twins were studied at the average age of 58 years on 34 phenotypic measures of personality, legal drug use and physical health and stature. Variation in age at separation and in degree of separation for reared-apart twins provides a unique opportunity to assess the long-term impact of rearing environment on bio-behavioural measures later in life. Multiple regression analyses indicated that the relationship between degree of separation and spirits and total alcohol consumption is in the expected direction; greater similarity in rearing environment leads to greater twin resemblance as adults, indicating the importance of shared rearing environment which accounted for 2 per cent of the variance in these measures. For personality the greatest number of significant effects were for number of years separated. However, the effects were small (accounting for at most 3 per cent of the variance) and significant primarily for identical twins. The results provide additional support for the hypothesis that environmental factors important to personality development are those experienced differentially by children from the same family, so called non-shared environmental influences.