Man is an animal and is subject to variation just the same as any other species of animal. An example of this is the enlargement of the fore-brain, with the corresponding mental capacity, from the Pithecanthropus, up through the Neander-thaloid and other intermediate types, to the Caucasian of to-day. So also is the development of the different varieties of the human species - black, brown, yellow, white, with all their subdivisions. How these variations came about are problems for ethnology, anthropology, and biology. Whether modifications - changes produced in one generation by its environment or mode of life - are transmitted to descendants, is an old biological question which seems to be still unsettled. Does the education of parents, for instance, predispose their children to receive education, entirely apart from its influence on the environment of the children? This question is of much importance to sociology and to education. The balance of opinion among biologists to-day favors a negative answer.

When different races inhabit the same region, a change in human nature goes on. One race will multiply faster than the others and so displace them in time, making its own qualities predominate in place of theirs. In this way the Polish race in eastern Prussia is displacing the German - or was, up to the disturbances caused by the World War - in spite of efforts by the government to the contrary. In France the Celtic element is displacing the Frankish or Teutonic. In the St. Lawrence valley the people of French descent are displacing the English.

There will also be intermarriage between the races. The result will be a hybrid stock which will be in some respects a blend of the two and different from either. With respect to some qualities inheritance follows the Mendelian law, a certain proportion of the children having the characteristics of one parent and a certain proportion the characteristics of the other. The following is an attempt to state the Mendelian law in concise form:

There are some qualities, called unit qualities, which are inherited without change. Hybrids, after the first generation, keep reverting to the original qualities of the ancestors. A certain proportion in each generation either possess a quality in its purity or else lack it altogether. The proportion depends on the law of chance, which, as we know, gives Uniform results for large numbers. Suppose for example that a boy has black marbles in one box and white ones in another, and then arranges his marbles in pairs by taking one from each box to make a pair. These pairs of marbles, composed in each case of one black marble and one white one, might be likened to the first generation of offspring from the crossing of two thoroughbred stocks; they are all hybrids; by no possibility can they be anything else. Now let the boy make pairs again by selecting marbles at random from the pairs already formed. The result will be, one fourth black, one fourth white and the remaining half both black and white. So the offspring of the hybrids will be one-fourth pure stock of one kind, one-fourth pure stock of the other kind, and one-half hybrids again. Now with regard to the hybrids there is a further complication. In them a unit quality sometimes becomes a blend with its opposite. If black Andalusian fowls are crossed with white, the hybrids are blue; then the offspring of these hybrids revert to the original types in the proportions given above. But some unit qualities never blend with their opposites even in the first generation; they are either present or else altogether absent. Thus if a full-blooded Swede marries a full-blooded Italian, the children will have the black eyes of the Italian; the quality of black eyes is "dominant," that of blue eyes "recessive." Then if this hybrid stock intermarries with its kind, one-fourth of the offspring will be blue-eyed like the Swedes, one-fourth will be black-eyed who if bred with their kind will have only black-eyed children - that is, with respect to eye color, they have become pure Italians; the remaining half will be black-eyed hybrids whose descendants will revert to the original pure types in the same proportions. If hybrids cross with either of the pure stocks, the same principle holds, only the proportions of the offspring reverting to the pure stock varies as mathematical computation would indicate. - Adapted from several accounts.

Unit characters are to all intents and purposes immutable, and they do not change during the lifetime of a language or an empire. The skull shape of the Egyptian fellaheen, in the unchanging environment of the Nile Valley, is absolutely identical in measurements, proportions, and capacity with skulls found in the predynastic tombs dating back more than six thousand years. - Grant, The Passing of the Great Race, pp. 15, 16.

The Mendelian law has been known such a short time that its application, especially to mankind and other slow-growing species, is still imperfectly understood. What qualities blend with their opposites and what qualities do not, what qualities are dominant and what are recessive, what qualities are unit qualities and what qualities are compound, what difference it makes whether the parent possessing a given quality be the father or the mother, - these are problems about which more will be known a century hence. But acquaintance with the Mendelian principle should be a part of the equipment of a teacher, who often has occasion to interpret a child's nature in the light of qualities found in the parents or grandparents.

It is clear enough that the crossing of varieties brings variation. With plants and lower animals there is once in a while a blend that will breed true; that is, the Mendelian law does not apply at all with respect to the original qualities composing the blend; a new quality is established at once. The same may be true of mankind. Furthermore, when two persons marry, especially if they come from different nationalities, they bring together two lines of heredity that run independent of each other many centuries back; their offspring, therefore, have combinations of qualities that were never made before. A quality may be a unit quality, following the Mendelian law, but still combine with the qualities that are not inconsistent with it and so make a new type of individual. Thus the crossing of Teutonic stock with Italian may combine the stature, honesty, and reasoning power of the Teuton with the complexion and delicacy of the Italian. St. Thomas Aquinas, the greatest scholar of the Middle Ages, very likely sprang from some such combination as this. Occasionally there is an atavism - the inheritance of a quality from some remote ancestor. Once in a long time there is just the right combination of qualities to produce an albino, or a genius, or a freak.

Variation in human nature brings with it variation in society. Professor Ross makes "the innovating individual" one of the eight stimuli to social change, and sometimes the resulting variation is great enough and sudden enough to constitute a mutation. Socrates, Philip of Macedon, Mohammed, Sir Isaac Newton, and Charles Darwin, unmistakably set great changes in motion. What the world would have been without them we cannot imagine.

. . . The genius is not a social but a vital phenomenon. Inventions and discoveries break in from what Professor James terms "the physiological cycle." Social destiny pivots on the advent of a brain that can invent gunpowder, the watermill, the compass, the printing-press, the locomotive - in a word on individual causes. At every instant a people has a number of paths open to it, and which one it will follow depends on those physiological variations which produce genius. ... - Ross, Foundations of Sociology, pp. 198, 199.

. . . The creative influence of personality can never be safely left out of account in sociology. ... - Ellwood, The Social Problem, p. 71.

. . . The initiation of all wise or noble things comes and must come from individuals; generally at first from some one individual. . . . - Mill, On Libertyj p. 119.

. . . Caesar was a social inventor when he established the principle that insolvency shall not cost the debtor his freedom. So was St. Paul when he conceived that the gospel was for Gentiles as well as for Jews. So was St. Benedict when he devised the "Rule" that gave form to the innumerable monastic communities of western Europe. So was Hilde-brand when he imposed sacerdotal celibacy upon the church. . . . Henry IV instituted the invalid soldiers' home. Grotius modified the relations of nations. Robert Raikes invented the Sunday school, Toynbee the social settlement, Le Claire the profit-sharing group, Raffei-sen and Schulze-Delitzsch the cooperative credit association. ... - Ross, Foundations of Sociology, pp. 232, 233.

Summing up at this point the several considerations which precede: we see that man possesses in the brain a sort of specialized adapting organ which relieves the rest of the body from the necessity of structural adaptation; that the human mode of adaptation is thus mental, and that it is also social. . . . The brain becomes the organ of adaptation .... - Keller, Societal Evolution, p. 39.