to the eldest son it may easily happen that great social differences are soon apparent even though the physical ancestry is the same. Because a child is born into a given social environment, among given people with whom he lives, and from whom he gets his language, customs and standards, we say that he inherits them. This is "social heredity." The medical man frequently uses the word "hereditary" when he means congenital, which is purely a chronological term referring to the date at which a given character appears, and in this sense has nothing to do with the origin of the characters. The medical man further offends by speaking of certain diseases as in: herited when he means only that they are transmitted to the child before birth. The venereal diseases are caused by specific organisms which may enter the body at any time and it is not correct to speak of them as inherited. We must be very careful then if we would avoid ambiguity to give a definite meaning to the term. Conklin has suggested the following: "Heredity may be defined as the appearance in offspring of characters whose differential causes are found in the germ cells." Strictly speaking we do not inherit eyes, feet or arms for the miniatures of these do not exist in the germ cell; but there is something within the cell which causes the development of the parts of the body. In this sense heredity will be used in these pages unless otherwise indicated. SUGGESTIONS FOR READING BATESON, W. Mendel's Principles of Heredity. 1909. 66 Problems in Genetics. 1913. CASTLE, W. E. Breeding. Heredity in Relation to Evolution and Animal 1911. CONKLIN, E. G. Heredity and Environment. (2nd Edit.) 1916. DARBISHIRE, A. D. Breeding and the Mendelian Discovery. 1911. DONCASTER, L. Heredity in the Light of Recent Research. 1911. HERBERT, S. First Principles of Heredity. 1910. Lock, R. H. Variation, Heredity and Evolution (2nd Ed.). 1909. LOEB, J. Artificial Parthenogenesis and Fertilization. 1913. MINOT, C. S. Modern Problems of Biology. 1914. REID, G. A. Principles of Heredity. 1905. THOMSON, J. A. Heredity. 1908. DEVRIES, H. Species and Varieties: Their Origin by Muta tion. 1905. WALKER, C. E. Hereditary Characters and Their Modes of Transmission. 1910. WALTER, H. E. Genetics. 1913. CHAPTER VI HEREDITY AND SOCIETY No two human beings are just alike and yet it is possible to divide the human race into great groups which resemble each other in fundamental characters and differ in details. Within a given group the differences between individuals may be as great as those which separate the groups themselves. It becomes possible therefore to subdivide the larger group into many smaller groups which possess this or that physical trait. We call the residents of the United States "Americans" and the word is definite enough for ordinary uses. We all know the component parts of this American people are very unlike, and the words "Whites," "Negroes" and "Indians" bring very different pictures to our minds. In like fashion we may split the white group into many sections. In making such a classification we may proceed to pick out the features in which differences are apparent and merely describe them, or we may consider them in their bearing on the state of society, the possibility of education and civilization. In a word man is always trying to explain social differences on the basis of physical differences, and the attempt is both fascinating and dangerous. In studying human heredity we are not satisfied then to describe what we see, but we try to correlate structure and achieve ment. As was mentioned in the last chapter it is now known that many human traits are inherited on a Mendelian basis. From the standpoint of society, some of these traits are matters of indifference in the main at least. We may know that curly, dark hair, brown eyes and dark skin are dominants, while straight, light hair, blue eyes and pale skin are recessives, and remain unmoved, for we do not see any close connection between these characters and ability. We are familiar with all these characters and have repeatedly seen them in persons of all walks of life and grades of ability. When the average observer learns that there are families characterized by hands quite different from the normal he is at once impressed, and wants to know whether these peculiar hands will not increase the difficulty of handling tools, of doing ordinary work, in other words, of earning a living. Such hands are rather rare and few people probably realize that they exist. Yet they do and they run for generations in a family and are moreover dominant over normal hands. There are three main types, those with an extra finger (polydactylic); those with short and stumpy hands and fingers (brachydactylic); and those more or less webbed between the fingers (syndactylic). Two of these are illustrated in the following diagrams: * |