TASKS, RESULTS, AND PROBLEMS OF RESEARCH ON TWINS ILLUSTRATED BY GOTTSCHALDT LONGITUDINAL-STUDY

The strong scientific interest in the relative importance of genetic f actors and variable environmental conditions with regard to the genesi s of interindividual differences in personality has, in recent years, led to an intensification of research on twins and on child adoption. Most of these studies rely on intelligence tests as well as personalit y questionnaires, and all of them are cross-sectional studies. By comp arison, GOTTSCHALDTS longitudinal study on identical and nonidentical twins now covers a period of more than 55 years. Furthermore, in addit ion to the quantitative information, diverse qualitative data based on the observation of and on interviews with the subjects are made avail able.