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In this book, Alessandra Piontelli summarizes her findings from a longitudinal study of twins. She conducted her study by following thirty pairs of Northern Italian twins from the moment their twinship was determined by ultrasound at ten weeks' gestation, through their third year of life. Half of her subjects are monozygotic twins, (Mz) half dizygotic (Dz). Her observations were obtained by interviewing parents both individually and as couples prepartum, by tracking the pregnancies during clinical and home visits, by videotaping the twin births, and by interviewing and videotaping the families at home postpartum on a regular basis for the next three years. She also took measurements in utero, and used various scales to obtain developmental and attachment data at intervals after birth.
Piontelli's stated goal in initiating this longitudinal study was to dispel the cross-cultural myths, superstitions, and pseudoscience that have arisen about twins. She questions the value of having used twin studies to “resolve controversy” about the nature /nurture dichotomy, where twins have become the medium through which to examine intricate behaviors and psychological phenomena that really require much more elaborate scientific method. Consistent with this protest, she makes the points that no single gene explains behavior, as in the prior view of one gene / one trait correspondence; that chromosomal expression is not “fixed” but is vulnerable to environmental influence for its expression; and that twin studies can be used only for singlegene diseases. Indeed, current genetic theory places the emphasis on plasticity, not destiny, and Piontelli couches her observations and data so as to emphasize the uniqueness of each twin. She enhances the scientific merit of her findings by cross-referencing her data across several disciplines, including embryology, obstetrics, anatomy, family and individual psychology, sociology, and psychoanalysis.