“…Psychologists from a variety of backgrounds, including both clinical psychology and behavioural genetics, have argued that sibling relationships in childhood may play an important role in the development of individual differences both in aggression 2ind in a wide range of other aspects of personality, intelligence and achievement (see, for example, Adler, 1982;Brim, 1958;Cicirelli, 1977Cicirelli, , 1978Dunn, 1983;Koch, 1960;Lamb & Sutton-Smith, 1982;Sutton-Smith & Rosenberg, 1970;Wagner, Schubert & Schubert, 1979). Behaviour geneticists have emphasized that siblings differ from one another on measures of personality and intelligence almost as much as do totally unrelated children reared in different families, although they share not only a greater proportion of their genes but also many aspects of the family environment.…”