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V.

THE first argument in favor of the view that the capacity for intelligence is hereditary is an argument by analogy. There is a good deal of evidence that idiocy and certain forms of degeneracy are transmitted from parents to offspring. There are, for example, a number of notorious families -- the Kallikaks, the Jukes, the Hill Folk, the Nams, the Zeros and the Ishmaelites, who have a long and persistent record of degeneracy. Whether these bad family histories are the result of a bad social start or of defective germplasm is not entirely clear, but the weight of evidence is in favor of the view that there is a taint in the blood. Yet even in these sensational cases, in fact just because they are so sensational and exceptional, it is important to remember that the proof is not conclusive.

There is, for example, some doubt as to the Kallikaks. It will be recalled that during the Revolutionary War a young soldier, known under the pseudonym of Martin Kallikak had an illegitimate feeble-minded son by a feeble-minded girl. The descendants of this union have been criminals and degenerates. But after the war was over Martin married respectably. The descendants of this union have been successful people. This is a powerful evidence, but it would, as Professor Cattell (1) points out, be more powerful, and more interesting scientifically, if the wife of the respectable marriage had been feeble-minded, and the girl in the tavern had been a healthy, normal person. Then only would it have been possible to say with complete confidence that this was a pure case of biological rather than of social heredity.

Assuming, however, that the inheritance of degeneracy is established, we may turn to the other end of the scale. Here we find studies of the persistence of talent in superior families. Sir Francis Gallon, for example, found "that the son of a distinguished judge had about one chance in four of becoming himself distinguished, while the son of a man picked out at random from the general population had only about one chance in four thousand of becoming similarly distinguished." (2) Professor Cattell in a study of the families of one thousand leading American scientists remarks in this connection: "Galton finds in the judges of England a notable proof of hereditary genius. It would be found to be much less in the judges of the United States. It could probably be shown by the same methods to be even stronger in the families conducting the leading publishing and banking houses of England and Germany." And in another place he remarks that "my data show that a boy born in Massachusetts or Connecticut has been fifty times as likely to become a scientific man as a boy born along the Southeastern seaboard from Georgia to Louisiana."

It is not necessary for our purpose to come to any conclusion as to the inheritance of capacity. The evidence is altogether insufficient for any conclusion, and the only possible attitude is an open mind. We are, moreover, not concerned with the question of whether intelligence is hereditary. We are concerned only with the claim of the intelligence tester that he reveals and measures hereditary intelligence. These are quite separate propositions, but they are constantly confused by the testers. For these gentlemen seem to think that if Gallon's conclusion about judges and the tale of the Kallikaks are accepted, then two things follow: first, that by analogy (3) all the graduations of intelligence are fixed in heredity, and second that the tests measure these different grades of heredity intelligence. Neither conclusion follows necessarily. The facts of heredity cannot be proved by analogy; the facts of heredity are what they are. The question of whether the intelligence test measures heredity is a wholly different matter. It is the only question which concerns us here.

We may start then with the admitted fact that children of favored classes test higher on the whole that other children. Binet tests made in Paris, Berlin, Brussels, Breslau, Rome, Petrograd, Moscow, in England and in America agree on this point. In California Professor Terman (4) divided 492 children into five social classes and obtained the following correlation between the median intelligence quotient and social status:

On the face of it this table would seem to indicate, if it indicates anything, a considerable connection between intelligence and environment. Mr. Terman denies this, and argues that "if home environment really has any considerable effect upon the IQ we should expect this effect to become more marked, the longer the influence has continued. That is, the correlation of IQ with social status should increase with age." But since his data show that at three age levels (5-8 years) and (9-11 years) and (12-15 years) the coefficient of correlation with social status declines (it is .43, .41 and .29 respectively), Mr. Terman concludes that "in the main, native qualities of intellect and character, rather than chance (sic) determine the social class to which a family belongs." He even pleads with us to accept this conclusion: "After all does not common observation teach us that etc. etc." and "from what is already known about heredity should we not naturally expect" and so forth and so forth.