In the introduction the problems of and access to human genetical gains of knowledge are described, especially the research theoretical paradigm of the classic twin method. The article shows: In the last decades with the help of twin research hereditary determinants have been found also for many (so-called and predominantly) psychogenic illnesses: For personality disorders, for psychoneurosis as well as for several psychosomatic illnesses. In the sense of a complementary list--more psychogenic/environmentally determined or primarily somatically/hereditarily determined--several normal characteristics and clinical pictures are listed.