The genius differs in _kind_ from the species, man. Genius can be defined only in terms of its own unique mental and temperamental processes, traits, qualities, and products. Genius is another psychobiological species, differing as much from man, in his mental and temperamental processes, as man differs from the ape.
_As a hypertrophied and highly specialized aptitude for specific performance_. The thought has been advanced that intellectual genius is a matter of specialization; that the mind of a genius will not, typically, work on all data with superior results, but that it is adapted only or primarily to certain kinds of intellectual performance. In other words, the genius is thought to lack general ability. A recent statement by Carrel (2) seems to express in part at least this theory:
There is also a class of men who, although disharmonious as the criminal and the insane, are indispensable to modern society. They are the men of genius. They are characterized by a monstrous growth of some of their psychological activities. A great artist, a great scientist, a great philosopher, is rarely a great man. He is generally a man of common type, with one side over-developed.
_As a combination of traits_. Galton (6) thought of genius as that which qualifies a person for eminence, and he believed that achieved eminence must be founded on a combination of no less than three essentials. He wrote:
By natural ability I mean those qualities of intellect and disposition which urge and qualify a man to perform acts that lead to reputation. I do not mean capacity without zeal, nor zeal without capacity, nor even a combination of both of them, without an adequate power of doing a great deal of very laborious work. But I mean a nature which, when left to itself, will, urged by an inherent stimulus, climb the path that leads to eminence, and has strength to reach the summit . . . one which, if hindered or thwarted, will fret and strive until the hindrance is overcome, and it is again free to follow its labour-loving instinct. It is almost a contradiction in terms to doubt that such men will generally become eminent.
We have seen that a union of three separate qualities--intellect, zeal, and power of work--are necessary to raise men from the ranks.