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 achievement.

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: *

*

Explanation of Diagrams: Shaded symbols represent individuals showing the character under discussion.

THE INHERITANCE OF POLYDACTYLISM 2

Dwarfs are not numerous, and yet are found in all parts of the world. They are ordinarily of low mental caliber, and are unfitted for ordinary employment. There are two general types. The achondroplasic type with large heads and stumpy limbs has a grotesque appearance. This condition is dominant over the normal. The ateliotic are diminutive specimens of ordinary proportions and

ACHONDROPLASIC 3

INHERITANCE OF DWARFISM

2 GUYER, M. F. o. c., p. 110.

ATELIOTIC 4

3, 4, PEARSON, K. Treasury Human Inheritance, Figs. 619, 708.

are recessive to the normal. Both conditions are heritable as the diagrams show, though the chart of the ateliotic type is incomplete and does not make clear its recessive character.

Deafness may be due to some sickness or accident but it is often the result of the inheritance of some peculiar ear formation. No one could consider deaf-mutism as anything but an undesirable affliction. It was known many years ago that the condition was more common among the children of affected families than in the population at large, and many family charts have now been made. These show that the condition may be passed on even though neither parent is affected, i.e., deaf-mutism is a recessive.

5

INHERITANCE OF DEAF-MUTISM

Hemophilia is one of the sex-linked traits, as before mentioned. The blood does not clot properly and hence even a slight cut may be dangerous or even fatal. In the family here charted the first six sons died as a result of this fact. It is to be noted that the daughters do not show the condition. They will transmit it to their sons but not to the daughters unless they chance to marry men who are also carriers.

5 PEARSON, K. o. c., Pl. X, Fig. 62.

• Ibid., Pl. X, 58.