Page:Popular Science Monthly Volume 35.djvu/289

when the processes are matured. By it is deduced an equation suggesting a theory of descent, to be applied in the subsequent investigations. The investigations were made by the aid of experiments on sweet peas (the sizes of the peas of a crop), and on moths bred for the purpose, and of about a hundred and fifty family records. The records, of course, include facts relating to a vastly larger number of persons. The chief subjects to which they relate arc stature, eye-color, temper, the artistic faculty, some forms of disease, marriage selection, and fertility. The item of stature offers many advantages in the study—from the ease and frequency with which it may be measured and its practical constancy during many years, from the fact that it is not a simple element, but is the sum of the accumulated lengths or thicknesses of many bodily elements, and because its discussion need not be entangled with considerations of marriage selection, and its variability is normal. To the inheritance of stature each mid-parent (median between the two parents) contributes an influence marked as one half, each individual parent one quarter, and each individual grandparent one sixteenth. A like hereditary relation is found to exist between the man and his ancestors in the matter of eye-sight. In point of the artistic faculty, highly artistic people intermarry, while moderately artistic people do not so usually, because, "A man of highly artistic temperament must look on those who are deficient in it as barbarians; he would continually crave for a sympathy and response that such persons are incapable of giving. On the other hand, every quiet unmusical man must shrink a little from the idea of wedding himself to a grand piano in constant action, with its vocal and peculiar social accompaniments; but he might anticipate great pleasure in having a wife of a moderately artistic temperament, who would give color and variety to his prosaic life. On the other hand, a sensitive and imaginative wife would be conscious of needing the aid of a husband who had enough plain common sense to restrain her too enthusiastic and frequently foolish projects." And vice versa. Of the problem as related to disease, the author observes: "The vital statistics of a population are those of a vast army marching rank behind rank, across the treacherous table-land of life. Some of its members drop out of sight at every step, and a new rank is ever rising to take the place vacated by the rank that preceded it, and which has already moved on. The population retains its peculiarities, although the elements of which it is composed are never stationary; neither are the same individuals present at any two successive epochs. In these respects a population may be compared to a cloud that seems to repose in calm upon a mountain plateau while a gale of wind is blowing over it. The outline of the cloud remains unchanged, although its elements are in violent movement and in a condition of perpetual destruction and renewal. . . . Both in the cloud and in the population there are continual supply and in-rush of new individuals from the unseen; they remain awhile as visible objects and then disappear. The cloud and the population are composed of elements that resemble each other in the brevity of their existence, while the general features of the cloud and of the population are alike in that they abide." One of the striking facts disclosed in the classification of the diseases of each family is their great intermixture. We know very little about the effects of such mixture, how far they are mutually exclusive, and how far they blend; or how far, when they blend, they change into a third form. Owing to the habit of free intermarriage, no person can be exempt from the inheritance of a variety of diseases, or of special tendencies to them. While death by mere old age and failure of vital powers appears common, it is not found, as a rule, that the children of persons who die of old age have any marked immunity from specific diseases. Applying the inquiry to consumption, the law of heredity found to govern the other faculties examined appears to govern that of liability to this disease also, although the constants of the formula differ slightly. It is not possible that more than one half of the varieties and number of each of the parental elements, latent or personal, can, on the average, subsist in the offspring; for a calculation based upon the supposition that they can all be conveyed would soon lead into absurdities. But if the personal and latent elements are transmitted on the average in equal numbers, it is difficult to suppose that