Mental Qualities Inheritable.—Galton showed by this method long ago, and Pearson and his school have extended and more clearly established the work, that exceptional mental qualities tend to be inherited. While on the average the children of exceptional parents tend to be less exceptional than their parents, still they are far more likely to be exceptional than are the children of average parents. By this method Professor Pearson has shown that such mental and temperamental attributes as ability, vivacity, conscientiousness, temper, popularity, handwriting, etc., are as essentially determined as are physical features through the hereditary endowment.
CHAPTER II
THE BEARERS OF THE HERITAGE
Before we can make any detailed analysis of the inheritance of characters we should have some general idea of the physical structure of animals and particularly some familiarity with the development of an individual from the egg, as well as some knowledge of the nature of the germ-cells.
The Cell the Unit of Structure.—If we examine one of the higher animals, as, for example, the horse, the dog, or man, we find that it is made up of a large number of constituents, such as bones, muscles, nervous elements, blood and other tissues. Each kind of tissue is composed of a number of living units, ordinarily microscopic in size, which are known as cells. A careful examination of various cells reveals that although they may differ greatly in size, shape and minor details, they all alike possess certain well-marked characteristics. Each when reduced to its fundamental form is seen to consist of a small mass of living matter termed protoplasm in which may usually be distinguished two regions—the cell-body or cytoplasm, and the nucleus (Fig. 3, [p. 21]). Any cell, whether it be of the brain, of the liver, or from any organ of an animal or plant, has this same fundamental structure. In addition, a limiting membrane or wall of some kind is generally present, although it is not a necessary constituent of all cells.
Fig. 3