The integrity of various parts of the brain is essential to the proper coördination of all the sensibilities and responses of the individual. Traits of character and types of ability, however, depend on the characteristic modes of reaction of the organism as a whole to the factors of its environment. Thus generosity as a human trait does not depend on the massiveness of any set of muscles, nor on the keenness of any sense-organ, but upon the characteristic type of reaction and motivation which the individual as a whole displays. Jealousy, love of children, destructiveness, etc., are characteristic modes of behavior of the whole organism, and depend upon reactions which the given situation evokes, and not upon some special organ.
2. As to the supposed correspondence between size and functional capacity, no evidence has been presented which demonstrates that even the strength of a muscle or the keenness of a sense-organ depends in any way on the absolute size of the brain-area concerned with it. Nor has evidence been presented to prove the existence, within any given species, of correlation between volume, shape, or weight of the brain-tissues and even the more general traits of character or ability. In the absence of such evidence we are led to believe that functional capacity depends on complexity of structure, chemical, molecular, and functional, rather than on the factors of mass or shape. But even the nature of these correlations is as yet largely unknown. The persistence of the faith in the significance of mass and shape probably rests in part on the apparent existence of such correlation when different species are roughly compared with one another. Thus, among the higher vertebrates there seems to be a relation between what we may call the general intelligence of the species and the erect carriage of the body. From the quadrupeds, with their horizontal position, through the apes, with their semiperpendicular mode of life, to the human being, with his erect carriage, there is also a progression in prominence of the forehead, opposition of thumb and finger, relatively greater development of the cerebral mass, and also in mental capacity. The intelligent human being walks in a more erect posture than does the stupid ape. But no one has ventured to assert that a relation exists between erectness of carriage and mental ability when human beings are compared with one another, or when apes are compared with one another. Similarly in the case of the physical features of the brain, the crude relationships which exist empirically, as between different species, seem to be quite slight in significance when compared with the differences in chemical, molecular and functional complexity which are found among members of the same species. Attempts to discover correlations between mental and moral characteristics and various brain constants we may expect to continue for a long time. What discoveries may be in store for us we do not know. But the important point in the present connection is that, for the purposes of vocational psychology, the practices of phrenology are based on evidence no more relevant to its pretensions than were the "proofs" pointed to by palmistry, horoscopy, and prenatal magic. Through cranial measurements alone it is impossible to determine with certainty the race, age, or sex of an individual, or even, indeed, whether he was a prehistoric savage, an idiot, or a gorilla.