| Abstract: | The scores of about one thousand Scottish eleven-year-old twins on a group intelligence test are compared with those of a similar group of about seven thousand non-twin children. The average score of the twins is found to be significantly lower than that of the non-twins. This difference is examined in connexion with the age of the child's mother, the degree of overcrowding in the home, and the occupation of the father. The mothers of the twins are found to be significantly older than those of the non-twins. The relationship of twinning and fertility is examined. There is also a slight predominance of twins in the higher social classes. Despite differences in family structure and social environment, the twins remain of lower average. intelligence throughout. |
