Page:Popular Science Monthly Volume 85.djvu/326

322 which organisms show, as well as all of their resemblances, are due to differences or resemblances in the hereditary and environmental factors which have been operative in their development. But in view of this universal variability of organisms it is not surprising that inheritance has seemed capricious and uncertain—"a sort of maze in which science loses itself."

Francis Galton was one of the first who attempted to reduce the mass of conflicting observations on heredity and variation to some system and to establish certain principles as a result of statistical study. He was the real founder of the scientific study of inheritance, he created characters singly and he introduced quantitative measures. Galton's researches, which were published in several volumes, consisted chiefly in a study of certain families with regard to several selected traits, viz., genius or marked intellectual capacity, artistic faculty, stature, eye color and disease. As a result of his very extensive studies two main principles appeared to be established:

1. The Law of Ancestral Inheritance which he stated as follows:

The two parents contribute between them on the average one half of each inherited faculty, each of them contributing one quarter of it. The four grandparents contribute between them one quarter, or each of them one sixteenth; and so on, the sum of the series 1/2 + 1/4 + 1/8 + 1/16 ... being equal to 1, as it should be. It is a property of this infinite series that each term is equal to the sum of all those that follow: thus 1/2 = 1/8 + 1/16 + ..., 1/4 = 1/8 + 1/16 + ..., and so on. The prepotencies of particular ancestors in any given pedigree are eliminated by a law which deals only with average contributions, and the various prepotencies of sex with respect to different qualities are also presumably eliminated.

 The mean height of all parents is shown by the dotted line between 68 and 69 inches. The circles through which the diagonal line runs represent the heights of graded groups of parents and the arrow heads indicate the average heights of their children. The offspring of undersized parents are taller and of oversized parents are shorter than their respective parents. (From Walter.)