Professor at Harvard University; Author of "Mankind at the Crossroads" HIS is a courtesy title like that of the retired army officer. Heredity had been until lately the master riddle of science. Twenty-five years ago it was a synonym for mystery and a text for discourses on the unknowable. Not so to-day. In a quarter of a century laws of heredity have been formulated as definite and precise as those of physics and chemistry. The mechanics of the two tiny cells which unite to hand the spark of life from generation to generation in our world of animals and plants have been analyzed with a clear-cut accuracy hardly to be expected when dealing with such entangled phenomena. Without overstepping fact one may say that genetics, the science of descent, has been the most profitable branch of twentieth-century biology. The term profitable refers primarily to the world's intellectual advancement and not to financial gain, but even with the latter meaning in mind one can make some rather broad claims legitimately. Genetics has made possible better strains of livestock. Meat production is more rapid. Food utilization is more efficient. Disease is less to be feared because of resistant stocks. Milk yields are increasing steadily. Both sheep and goats produce longer and stronger wool, or finer and more glossy wool, according to the heritage allotted them. New types specialized for different purposes are constantly being created. Novel varieties appear in increasing numbers year by year, and though the great majority of them are probably little better than the older types they are designed to replace, here and there a strain stands out whose inherent merits make it worth millions. In fact, if one studies the chief varieties of farm crops now grown, he finds scarcely a single one which was known to the world fifty years ago, so rapid has been the man-made evolution of the vegetable kingdom. All of this is very interesting and important, no doubt. A dinner, a pair of shoes, and an overcoat are matters of moment to the shivering wretch at the rôtisserie window; and those who make them easier to obtain deserve our gratitude in lieu of the royalties we do not pay on their discoveries. But no biologist likes to feel that the true goal of genetic work lies in adding loaves of bread and bales of wool to the world's supply. He fervently hopes to aid those functions of mankind which rate somewhat higher than alimentation, believing as he does, with Anatole France, that food ingestion is a humiliating process which might well have been relegated to a larval stage after the manner of the insects. Inscribed on the Delphic oracle were the words "Know thyself," and this, says Cervantes, "is the most difficult lesson in the world." Here is a motto twenty-five hundred years old which, like most aphorisms of its kind, has been im Among plants there is the same story. I VOL. LXXVIII.-1 possible of realization. Only. in the twentieth century has mankind. begun to peer behind the veil which shrouded his inmost nature. How can one know himself when in ignorance of the endowments which make him what he is? The individual is wholly and solely the product of his heredity and the environment in which he finds himself, and unless he endeavors to learn what he can regarding the limitations and the possibilities thus allotted, he does no justice either to himself or to his posterity. We may rebel against a statement which assigns to free will a narrow choice, we may poke fun at what many have called "Calvinistic predestination in scientific guise"; but the facts remain. Let us think a moment, however, before we scoffingly pass judgment. Is a feebleminded child likely to become President of the United States? Will the boy with a club-foot win medals at the stadium? Can the individual with a cleft palate become an orator of note? Of course they cannot do these things. Their heredity circumscribes their world. Is it strange, therefore, that there should be bounds for each one of us beyond which we cannot pass? Yet this idea is the homologue of predestination only in part, and therein lies hope. What genetics tells us is that heredity allots to each certain possibilities; whether these possibilities are fulfilled wholly or in part depends upon circumstances. The only sure prescription for a tall and stately mien is a proper ancestry; but if one wishes to make the best of the bargain after having had his ancestors chosen for him, he should look to his food, his rest, his recreation, and his habits. A child will not become great unless he has greatness in his make-up, but he will not become great under any circumstances if his talents are kept rolled up permanently in the proverbial napkin. It is unlikely that a time will ever come when the expert can predict with accuracy what will be the outcome of each and every human mating. Certainly no one wishes to try to select parents or to forbid parentage except in rare cases where The legacy to the next generation is pracically certain to be a terrible thing. But even now one has the opportunity to learn much regarding his or her genetic possibilities by interpreting their ances tral histories in modern genetic terms. One can predict absolutely whether a certain union will or will not produce numerous dominant abnormalities which are only too common in the human race. He can predict with relative accuracy— that is to say, he can calculate the chances for and against-whether this same union will produce mental and physical defectives of the recessive type the type which can lie hidden for a series of generations. Such information is useful, and it is to be hoped that more and more persons will come to use it for the sake of their own happiness. The good of the race will be promoted thereby, but this need not enter into their consideration. Individual selfishness can here act as a stimulus to racial betterment. There is, however, a use to which genetic knowledge may be put which probably has even greater social significance than the one just mentioned. The processes by which hereditary traits are handed on cannot be described with the simplicity and elegance of the law of gravitation. Being somewhat complex, and disturbed by many conditions not easily controlled, they can often be dealt with more easily by considering averages only. In this they are a good deal like life insurance, where calculations which. give very accurate results when large numbers are concerned, are relatively useless for individual cases. In the same manner, the generalized findings of genetics have possibly their most pertinent application to problems of social welfare. They may not often give us an immediate solution to the difficulties which our complex society finds at every turn, but with them in mind one does have the questions involved sharply defined. Are you a lawyer? Genetics gives you a better conception of where human responsibility begins-and ends. Are you a minister? It shows how variable are the needs of spirit and of body among different individuals. Are you a physician? It enlarges your opportunities for successful treatment of all the various human ills, for the hereditary endowment of each one of us looms large in every pathological condition. If you are none of these, if you are one of the millions of citizens whose vocations seem to imply about as much usefulness for this type of biological knowledge as for training in the integral calculus, do not forget that you live in a democracy and have a vote. You will be called upon time and again to make a personal decision as to the merits or demerits of various proposals relating to marriage and divorce, to education, to immigration, to conditions of living which affect the public health, and to various other matters which concern the welfare of this and of future generations. And, as Wiggam says, "one can approach very few of such problems intelligently without some knowledge of heredity, because he is then in total ignorance of one of the largest forces that enter every moment into human life, human character, and social destiny." So much for our plea that a public hearing be accorded to genetic results. It is the outgrowth of such a sincere conviction that it would need no apology even if the statements were emphasized again and again; but it is a cardinal point in advertising one's wares to shift to an actual demonstration of merits before the prospect is quite bored to tears by exultant panegyrics. Unfortunately, this latter task is beset with difficulties. One must admit it even though such a frank avowal is the height of rashness. The primary intention in this article is to give an outline of genetic philosophy, to put down in as few words as possible the essentials of the general conception of heredity which has grown out of the fifty thousand or more original researches on the subject that have been published during the past quarter of a century. And there's the rub. One is all at sea in any science without a grasp of the generalizations; and generalizations, though easy enough to understand, are far from being entertaining. Specific illustrations, how sex is inherited, what makes one man tall and another dwarf, how inbreeding uncovers the defects that are the only really genuine family skeletons, these are interesting enough to divert the weary; but the trouble is, they cannot be appreciated properly without a little preliminary drudgery on principles. The reader is invited, therefore, to consider this essay in the light of an initiatory training designed to show whether he is worthy to become a repository of the esoteric secrets of the cult. The visitor to the genetic laboratory, wishing to appear sophisticated, often says, "Oh! you are studying the Mendelian Law," a remark which wearies the professional host more than a week of hard labor. With as much justice one might ask the chemist if he is studying the Daltonic hypothesis or the physician if he is applying Galen's rules. Yet there is this to be said: the beginning of the study of heredity as an exact science does date from the first real appreciation of Mendel's experiments on the garden pea carried out in the tiny monastery garden of the Moravian town called Brünn; and this was only twenty-five years ago. Genetics was born and christened because of Gregor Mendel, not because he was such an intellectual giant that he could analyze and codify the complex results which had baffled his predecessors in hybridization work, but because he had the really brilliant idea of simplifying his experiments to the point where he was dealing with only one or two variables at a time. Where heretofore botanists had crossed plants differing by hundreds of characters and had been bewildered at the apparent chaos of their data, Mendel used varieties which differed by one single character. This lone character he followed through generation after generation with the carefulness of a master workman, and obtained results so simple that he was able to give them their correct interpretation. Only when he was satisfied that he knew what happened when one character was under consideration, did he try to steer his way through the maze of complications produced when varieties differing by two or three characters were used. We have passed far down the road since then, but on looking backward we see that Mendel's work was merely the first clearly carved milestone and not the beginning of the highway. The immense amount of study of the results of carefully controlled matings among both animals and plants all has pointed to a single type of cell mechanics as the basic feature of heredity. It is the same for man, monkeys, mosquitoes, and melons. Sexually reproducing animals and plants, whatever their type, wherever their habitat, varied as may be their manner of living, behave in the same way as regards inheri |