We distinguish between the general factors in intelligence, just mentioned, and special aptitudes for dealing with colors, forms, numbers, weights etc. A special aptitude is a specific responsiveness to a certain kind of stimulus or object. The special aptitudes are factors in intelligent behavior--as we may judge from the content of the intelligence tests--only, the tests are so contrived as not to depend too much on any one or any few of the special aptitudes. Arithmetical problems alone would not make a fair test for intelligence, since they would lay undue stress on the special aptitude for number; but it is fair enough to include them along with color naming, weight judging, form copying, and word remembering, and so to give many special aptitudes a chance to figure in the final score. There are tests in existence for some special aptitudes: tests for color sense and color matching, for musical ability, for ability in drawing, etc.; but as yet we have no satisfactory list of the special aptitudes. They come to light when we compare one individual with another, or one species with another. Thus, while man is far superior to the dog in dealing with colors, the dog is superior in dealing with odors. Man has more aptitude for form, but some animals are fully his equal in sense of location and ability to find {289} their way. Man is far superior in dealing with numbers and also with tools and mechanical things. He is superior in speech, in sense of rhythm, in sense of humor, in sense of pathos. Individual human beings also differ markedly in each of these respects. They differ in these special directions as well as in the "general factors" of intelligence. Heredity of Intelligence and of Special Aptitudes Let us now return to the question raised at the very outset of the chapter, whether or not intelligence is a native trait. We then said that the differing intelligence of different species of animals must be laid to their native constitutions, but left the question open whether the differing intelligence of human individuals was a matter of heredity or of environment. Intelligence is of course quite different from instinct, in that it does not consist in ready-made native reactions. The intelligence of an individual at any age depends on what he has learned previously. But the factors in intelligent behavior--retentiveness, responsiveness to relationships, persistence, etc.--may very well be native traits. But what _evidence_ is there that the individual's degree of intelligence is a native characteristic, like his height or color of hair? The evidence is pretty convincing to most psychologists.