It has been proposed that the effects of a phenomenon referred to as the identical-twin transfusion syndrome reduces estimates of the degree of intelligence attributable to heredity (Munsinger, 1977). Munsinger presents evidence to illustrate the size of the effect and the results when a correction for this effect has been made. A close examination of the original data used by Munsinger, however, provides no clear support for differences of the order he calculated. It is principally the arbitrariness and lack of regard for factual details when his data was classified that leads to this conclusion.