Personality and Birth Order in Monozygotic Twins Adopted Apart: A Test of Sulloway's Theory; Research Reviews: Twin Births and Cancer Risk in Mothers, Male Sexual Dysfunction, Twin Study of Ultimatum Game Behavior; Human Interest: ‘The Land of Twins’, Twin-Like Reunion-I, Twin-Like Reunion-II

Abstract

A brief overview of Sulloway's (1996) theory of birth order and personality is presented. A reared apart twin approach for testing his personality findings regarding openness to experience and conscientiousness in first borns and later borns is described. This is followed by summaries of three recent twin studies. The topics include cancer risk in mother of twins, sexual dysfunction in males and responder behavior during ultimatum games. This article concludes with a discussion of twinning rates and rituals among the Yoruba of western Nigeria, and descriptions of two unusual reunions between siblings and twins.