M jr ONOZYGOTIC AND DIZYGOTIC TWINS WHO WERE SEPArated early in life and reared apart (MZA and DZA twin
pairs) are a fascinating experiment of nature. They also
provide the simplest and most powerful method for disentangling
the influence of environmental and genetic factors on human
characteristics. The rarity of twins reared apart explains why only
three previous studies of modest scope are available in the literature
(1-4).