Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart

Abstract

Since 1979, a continuing study of monozygotic and dizygotic twins, separated in infancy and reared apart, has subjected more than 100 sets of reared-apart twins or triplets to a week of intensive psychological and physiological assessment. Like the prior, smaller studies of monozygotic twins reared apart, about 70% of the variance in IQ was found to be associated with genetic variation. On multiple measures of personality and temperament, occupational and leisure-time interests, and social attitudes, monozygotic twins reared apart are about as similar as are monozygotic twins reared together. These findings extend and support those from numerous other twin, family, and adoption studies. It is a plausible hypothesis that genetic differences affect psychological differences largely indirectly, by influencing the effective environment of the developing child. This evidence for the strong heritability of most psychological traits, sensibly construed, does not detract from the value or importance of parenting, education, and other propaedeutic interventions.

Genetics of the human electroencephalogram (EEG) and event-related brain potentials (ERPs): a review

“…For (z-parameters, enough evidence seems to exist to conclude that genetic factors contribute significantly to variations in c~-amplitude and c~-index. The high concordance in MZ twins is also seen in MZ twins reared apart (Bouchard et al 1990), suggesting that common environmental variance is not an important factor. Use of spectral analysis of the EEG has led to high heritabilities being shown for various frequency bands.…”

“…This is slightly less than a person resembles himself over time. With the same procedure, Stassen et al (1988a, b) analyzed EEGs of MZ and DZ twins reared apart (Bouchard et al 1990). The previous results were confirmed; the similarity of MZ spectral patterns is only slightly less than that of the same subject compared with himself over time, and the average similarity of the DZ pairs differs significantly from the similarity of a group of UR individuals.…”

Genetic variation in MAOA modulates ventromedial prefrontal circuitry mediating individual differences in human personality

“…The validity of this approach is bolstered by evidence that the majority of personality traits appear to be moderately to highly heritable, with only minor influences of individual environment in twins reared apart. 10,11 Following the Cloninger model, much of this work has focused on candidate genes affecting monoaminergic neurotransmission and their prediction of variation in temperament ratings on instruments such as the TPQ. However, even for the most widely studied such gene, a promoter variant in the serotonin transporter (5-HTTLPR), a consistent picture has not emerged.…”

Blood pressure and its reactivity in the offspring of first cousin hypertensive and first cousin normotensive parents: a preliminary report

“…4,5 Twins, family and adoptive studies have shown that at least 50-79% of the blood pressure variation in humans can be attributed to genetic factors. 6,7 Compared to the offspring of two normotensive parents, blood pressure is higher in the offspring of one normotensive and one hypertensive parent, and highest in the offspring of two hypertensive parents. 8 These distributions are evident in infancy and persists through late adulthood.…”