3. If, as seems quite likely, it be ultimately demonstrated that there are some characteristics, aptitudes and capacities that depend directly on congenital endowment, special nervous and sensory characteristics of a valuable kind, we may mark off another group of occupations for which particular individuals are well adapted, though not exclusively so, by original nature. Among the traits which have been said to occur in some such direct hereditary way, or as the result of unexplained mutation or deviation from type, are: mathematical aptitude, ability in drawing, musical composition, singing, poetic reaction, military strategy, chess playing. Maternity, as a vocation, is of course strictly sex limited. Pitch discrimination seems to depend on structural factors which are not susceptible of improvement by practice. The same may be said of various forms of professional athletic achievement. Color blindness seems to be an instance of the conspicuous absence of such a unit characteristic. "Poets," it is said, "are born, not made." Many of these apparent unit characteristics are so relatively independent that they often occur in quite surprising degree in individuals who are otherwise imbecilic. Mathematical, musical, graphic and decorative aptitudes, mechanical memory, and certain types of manual dexterity and mechanical cunning are frequently exhibited by the _idiot savant_. By the _idiot savant_ is meant an individual who is in most respects mentally defective, who perhaps cannot dress himself, cannot adequately learn to speak or write, but who possesses some particular ability to a surprising degree. Such individuals may be able to perform on various musical instruments, to compose music, to sketch designs and objects in an imitative manner, to remember long lists of disconnected names or numbers, to weave acceptably such articles as rugs and scarfs, or to construct complicated mechanical objects such as furniture, pumps, and sailing vessels. Cases of rare possession of unit characters constitute the "genius" of ordinary conversation. These seem to present no problem for vocational psychology. Their marked unusualness renders them sufficiently obvious, even to the individual who does not systematically analyze himself. Such a prodigy requires a generous friend and an opportunity rather than a vocational expert.