How often we hear someone remark upon the wonders of heredity. People are astonished because John should look like John's father. As a matter of fact, the astonishment should come the other way. The child is but a continuation of the life of the parents. The cells from which the child develops have within them the power to grow and to produce individuals like the parents. This is wonderful, but it is only another form of the wonder of a willow twig growing into a willow tree when placed in moist earth.

To the scientist, then, the wonder comes, not in the fact that the child resembles the parent, but in the fact that the child is not identical with the parent. Part of the explanation of this lack of identity, or, as it is known to science, variation, is due to the fact of sexual reproduction; that is, to the fact that the child has two parents instead of one.

Why The Child Is Not Identical With Parents

The physiological process which takes place in the union of two reproductive cells is truly most wonderful. Of late years this has been studied under powerful microscopes and has resulted in some very wonderful revelations of the mysteries of Nature.

Microscopic Study Of Reproductive Cells

The nucleus (center of growth) of the parent cells contains little thread-like structures known as chro-niosoms. These chromosoms are considered to be the physical basis of heredity. In each species of animal there is a definite and a different number.

Chromosoms In Different Species

When the sperm-cell unites with the female or germ-cell, these thread-like chromosoms pair off and unite each chromosom with the corresponding structure from the other cell. The combined structures then divide, and half of each chromosom is cast out of the cell-nucleus, and plays no part in the life of the future being; the other half is retained and divides as each new cell is formed.

Action Of The Chromosom

Thus we see that every part of the new individual is the result of the fusion or combination of the two parents. This explains the variation of inheritance, and through this source must be traced all traits of heredity. After the original fusion of these microscopic physical elements of heredity, the future development of the individual is wholly a matter of environment and nutrition.

What Heredity Is

What heredity is and what it is not will now be considered in a practical way. It is clearly a matter of heredity that a man is born a man and not a monkey. Likewise, it is clearly a matter of heredity that distinguishes the various races of men. We could go farther and trace out and describe many of the physical distinctions which mark families, and even individuals, such as general size of frame, form of countenance, color of hair and eyes, etc.

General Characteristics Due To Heredity

Among mental traits we can safely ascribe to heredity only general distinctions. Intellectual parents are more likely to give birth to intellectual children than are parents whose natural mental faculties are less developed. There is also no doubt that certain natural characteristics of mind, such as quick temper, musical ability, etc., may be inherited. The belief, however, in the inheritance of many less distinct features, both physical and mental, is not well established by scientific investigation. Strength of muscle, control of the nervous system, susceptibility to, or freedom from disease, etc., are more matters of nutrition and environment than of inheritance. The idea that consumption, alcoholism, etc., are in-herited, or that the education or training of parents along certain lines will result in children with faculties adapted to similar education, is not in accordance with scientific knowledge.

Characteristics Not Attributed To Heredity

Summary Of Facts Regarding Sex And Heredity

1 The function of sex has been developed in the process of evolution for the purpose of perpetuating life.

2 The sexual functions are very closely related to the life of the individual, and can be normal only when the laws of nutrition and of general hygiene are observed.

3 The idea of prenatal culture as commonly taught is a delusion; the only method that the mother can employ to control the growth of her unborn child is to live a wholesome, normal life, physically and mentally, and thus supply her own body and that of the child with perfect material for the building of living cells.

4 The powers of heredity are often overestimated, and many of the weak-nesses and disorders of life supposed to be inherent can be overcome by proper nutrition and environment. All life, whatever be the inherited tendencies, will be developed to the highest possible capacity by obeying the laws of individual growth, for in the individual, as in the race, Nature is always striving to bring the products of her work to the highest degrees of perfection.