Psychophysiology of Monozygotic Male Twins

THE SPECIAL psychology of the individuals who comprise a pair of identical twins has recently attracted considerable interest.^1-7 Difficulties in their establishment of a sense of individual identity as well as unusual patterns of alliance and aggressive competition have shed light on certain aspects of developmental psychology and character formation in nontwins.

Our observations of twins were part of a larger study⁸ of supposedly healthy males most of whom were recruited as research subjects from neighboring colleges where they were students. The aim of the project was to correlate personality structure with relatively constant homeostatic patterns during phases of everyday life experience as measured by certain endocrine and exocrine indices of hypothalamic response. We have focused on the urinary excretion of 17-hydroxycorticosteroids (17OHCS), measured by the method of Reddy et al,⁹ and 17-ketosteroids (17-KS), determined by a modification of