cludes certain eye colors; certain hair colors and hair forms, such as straight, wavy, and curly; certain skin colors, such as that of the blond and the brunette; pale, fresh, and colored complexions in the white race; stature, form of head, and nose in certain races; various deformities and defects, such as short fingers, aborted fingers, split-fingers, split-foot, cataract, certain hair deficiencies, stationary night-blindness, certain sex-limited diseases like hemophilia, and color-blindness; and certain kinds of deaf-mutism, insanity, and imbecility. Thus even at this early stage in the study of human heredity, there is good reason to believe that many of our traits Mendelize."9 Some of these which are of social significance will be discussed in a later chapter. Here we are attempting to state the case only.

In the human eye when the coloring matter exists only on the inner side of the iris the color is blue or gray. If there is also a layer of pigment on the outer side of the iris the color is brown or black. Experience shows that brown is dominant, blue the recessive. Two blue or grayeyed parents can never have brown-eyed children since there is evidently no factor for brown on either side of the family. If the parents are duplex brown they cannot have blue-eyed children, while if they are simplex brown one-fourth of the children will have blue or gray eyes.

Hair color and hair shape seem also to be Mendelian traits though hair color is due to two pigments, black and red. Dark hair seems dominant to light, and curly hair is dominant to straight.

We must now ask whether these unit characters are fixed or whether they may be modified. De Vries thought

9 PARKER, G. H. Biology and Social Problems, pp. 94-95.

they were as distinct from each other as the chemical elements. Castle and others, by experimenting upon guinea-pigs and hooded rats, have introduced by artificial selection what they regard as marked modifications of unit characters. Castle feels that the unit characters themselves are probably variable. Bateson puts it thus:

"Elements exist in our domesticated breeds (of chickens) which we may feel with confidence have come in since their captivity began. Such elements in fowls are dominant whiteness, extra toe, feathered leg, frizzling, etc., so that even hypothetical extension of the range of origin is only a slight alleviation of the difficulty.

"Somehow or other, therefore, we must recognize that dominant factors do arise. Whether they are created by internal change, or whether, as seems to be not wholly beyond possibility, they obtain entrance from without, there is no evidence to show." 10

Attention has been called to the fact that the men of Darwin's time put great emphasis on the very slight changes in the organism and thought that the "sports as they called the marked departures from the normal had little meaning and little chance of survival inasmuch as they would be lost in the average if mated with the ordinary type. It is known today that many of the "mutants" do not revert but breed true and we know, further, that it is possible to combine different units from different plants and perhaps produce a plant superior to the old type. Thus the English wheat has been greatly improved by combining types having grain which possessed the desired qualities with other types whose stems were immune to rust. The beet of Napoleon's time contained only about 3 per cent of sugar. By various crosses we now 10 BATESON, W. o. c., p. 90.

have beets grown commercially containing 16 per cent sugar and one of the experiment stations reports a type with 29 per cent sugar. If this last can be made commercially available one can easily imagine how valuable it will become. Other mutants which have proven useful are seen in the famous Concord grape and its later mutants, Worden, Moore's Early, and Pocklington. Nectarines are mutants from peaches; apricots from plums. The Hubbard squash is a mutant. The list of flowers which belong to this category is very large.

Objection has been brought against mutants on the ground that they are all hybrids and that the primroses on which De Vries worked were themselves the crosses of several American varieties. Whatever the truth of the charge the practical value of the combination of different characters remains and moreover the mutants often breed true. As regards any given trait an "extracted" individual may be just as 99 "pure as one of unmixed ancestry. Indeed this is one of the most important points in the Mendelian theory. Thus Darbishire crossed pure yellow with extracted green of the fifth generation. He got 139,817 seeds, of which 105,045 were yellow and 34,792 (24.88 per cent) were green. These green seeds bred just as true as the pure green.

There is much reason to think then that this conception of mutations is one of the most important in the field of biology. The minor fluctuations about a given form are practically constant and do not lead in any direction but a mutation, which seems to be a new chromosome combination, and may make the beginning of a new line. Furthermore it throws the emphasis upon the nature of the germ cell, not upon the external appearance of the parent. Punnett says, "As our knowledge of heredity

clears and the mists of superstition are dispelled, there grows upon us with an increasing and relentless force the conviction that the creature is not made, but born." 11

As was shown in the preceding chapter it was long believed that experiences, developments, injuries of one generation somehow or other were reflected in succeeding generations. So thought Darwin as well as Lamarck. Darwin, seeking to explain this, suggested that from the parts of the body affected went little bodies, called " gemmules," which in some fashion were incorporated in the germ cells. In current terms, it was thought that "acquired characters" were inherited. To avoid confusion, be it noted that "acquired characters" are changed in the arrangement of the body cells; that in some fashion these caused changes in the nature of the germ cells so that later generations were affected. The evidence for this seemed so abundant and conclusive, it so closely corresponded to common observation, that men no more thought of questioning it than did those of an earlier time question the revolution of the sun about the earth. Oddly enough, it was this very point which was attacked by Weismann, who came out in flat-footed opposition to the popular idea of the inheritance of acquired characters for he could discover no way in which body cell changes

produced any effect upon the germ cells. This bomb was exploded in 1885 and caused as much excitement in biological circles as the doctrine of evolution had produced in the ranks of the theologians.

It seemed easy to overthrow this new heresy and many series of experiments were started in the search for evidence. Among the best known were those of BrownSéquard who apparently succeeded in producing hereditary 11 PUNNETT, R. C. Mendelism, p. 60.

epilepsy and other defects by a series of mutilations of guinea pigs. At first these were considered conclusive but the same experiment repeated by others failed to produce similar results and hence they are today little regarded. In fact, thirty years have passed, no single clear case has been produced by Weismann's opponents and his main contention is held as established. Again we must note that it is a matter of indifference whether his explanations prove correct or not.

Weismann stated that changes in the body cells had no influence upon the germ cells. Most people little realize what a mass of corroborative evidence lies easily at hand. Every one knows that the sudden changes produced by accident or disease have no such effect. A man is marked by smallpox, but the skin of the children later born is smooth. The broken arm, the amputated leg, the scar of the wound or burn are equally without result. Suppose, however, that a similar condition affected many consecutive generations, might we not then see a result on the offspring? Among various groups of people for countless generations the teeth have been knocked out, the heads changed in shape as among the flat-head Indians, the feet bound as among the Chinese, ears and noses pierced, yet all without result on the race stock. To our knowledge Semetic peoples have practiced circumcision for three thousand years, but the sacred rite is as necessary as ever. The hair and beard grow, though cut for ages. Virgins still have hymens. Child-bearing seems to be more difficult and dangerous for civilized woman than it was for her savage ancestress. If all such changes be grouped under the head of mutilations, it seems fairly certain that they do not affect later generations.

If we consider these changes which we may call improve