Furthermore, musicality is not one specific human trait but an infinite hierarchy of traits running through the entire gamut of the psychophysical musical organism. To make any progress whatever, the scientist must make the supreme sacrifice of attempting to deal only with specific isolable factors apparently small and remote in themselves. The situation is analogous to that of purely physical features. It is generally admitted that the structure of the physical organism is heritable. But when we show that the color of the eyes of the fruit fly is heritable and that this inheritance takes place in a very complicated way, as has been adequately shown, we have simply identified parts of the structure and function of the genes in one specific feature in the vastly complex physical organism, however fundamental and characteristic this particular feature may be. This analogy applies in principle to the genetic study of the musical life. The crux of the difficulty lies in the identification of heritable factors. Again we must remember that the musical mind is first of all a normal mind, a normal psychophysical organism ready to begin to function immediately after birth. What we shall look for then in a psychophysical organism is the presence of certain resources especially favorable or especially unfavorable to the normal functioning of the musical mind. We may assume that an average capacity present in the genetic constitution may be adequate for musical purposes but that exceptionally gifted persons require these traits in a correspondingly exceptional degree and that exceptionally unmusical individuals lack essential elements. The most wonderful thing is that a person can come into the world with a musical constitution at all, but the problem of heredity centers around individual differences, and these are more easily approachable than the total function. As in genetic studies of the inheritance of color blindness it has been possible to identify types, so in musical hearing we may look forward to the identification of types of defect and types of superiority deviating markedly from the normal.