One of the first studies on testing homosexuality using twins was in 1952 by Frantz Kallman. Kallman’s study had 85 sets of twins. 40 sets out of 85 sets of those twins were monozygotic (identical twins) and the other 45 sets of twin were dizygotic (not identical twins). This study also included 112 individuals who were not twins but were homosexual and it also included 116 employees from Kallman psychiatric institute. All of the homosexual people either came from his psychiatric institutions or prisons (kallman 1952). Kallman concluded that his study plainly diminishes the plausibility of studies which overstress the importance of such precipitating or perpetuating factors as social ostracism, incompetence of a particular parent, or other
