Dominance and submissiveness between twins. I. Perinatal and development aspects.

Factors predicting dominance and submissiveness between twins were analyzed in a longitudinal study of 234 twin pairs. Boys were found to be physically dominating, while the girls more often were psychically dominating and in the role of the spokesman. Low birth weight, to be second born, or low Apgar score tended to predict submissiveness, but not significantly. The same was true concerning perinatal asphyxia and hypoglycemia, which also showed some potential cumulative effect when occurring simultaneously. Those having developed faster or with higher intelligence were more often the leaders of the twin pair. Probably good neonatal care in modern hospitals tends to prevent perinatal damage, and therefore the previous findings of second born or small birth weight twins being most submissive was not fully established.