Page:Popular Science Monthly Volume 76.djvu/422

418 obvious, though how easy of application remains to be ascertained. Would a farmer expect to have full harvests if each year he saved seed from the poorest yielding plants, or could he hope to secure the best results from his herds by selling or butchering the best stock and keeping only the scrubs? Obviously not, and no more can the civilized nations maintain their present standards of manhood if they follow a like practise.

But before any serious attempt can be made to improve the human race considered as an assemblage of animals possessed of certain desirable physical and intellectual attributes, it is obvious that we must know something about heredity in general, and how in particular each of the desired physical and intellectual attributes is produced. Considerations such as these lend general interest to the study of heredity, a subject which has always been of great practical concern to farmers, and of much theoretical interest to scientists. It is my purpose to review briefly some of the problems which the study of heredity presents, and some of the results obtained from their consideration.

"Like father like son" is a homely proverb which shows how general the recognition is that children resemble their parents. Resemblances to grandparents or ancestors even more remote are also of frequent occurrence, and it is convenient to use the term heredity as including all such resemblances, whether to near or to remote ancestors. The phenomenon of heredity is of course not restricted to human society. Heredity has for the stockman and plant-breeder a well-recognized commercial value, because by a knowledge of its laws he is enabled to produce in greater number or with greater certainty animals or plants of a particular type. Indeed, much of our present knowledge of heredity has been derived from a study of the domesticated animals or of the cultivated plants, and from the same sources we may expect to continue to draw, for here alone have we an unobstructed field for observation and experiment, the indispensable tools of scientific research. Just as the sciences of anatomy, embryology, physiology and pathology progressed but slowly so long as the phenomena of the human body alone were considered, but advanced by leaps and bounds when comparative studies on other animals were undertaken, so concerning heredity in man we have learned and can expect to learn but little from the study of man alone, but much from a study of other animals and of plants and from a comparison of the phenomena in the two cases.

Every new individual arises out of material derived exclusively from its parents. This is the basis of heredity. But it does not follow that the new individual will resemble its parents merely. It may resemble remote ancestors more strongly than either parent. For it represents a combination of materials or of qualities derived from the two parents and it is possible that neither parent may manifest all the