If something beyond mere knowledge of right and wrong always has been necessary, and is likely to be necessary for some ages to come, among adult persons, to deter many of them from violating the laws of society and of their own health; if persons need the fear of penalty in the way of illness, helplessness, and suffering to aid them in conforming to obedience, how much more necessary it is in relation to the young, whose experiences have been so limited, and whose reason is so immature. Hence it is, that the parent and the educator must not only _instruct, but enforce obedience_. CHAPTER VIII. HEREDITY. It may be remarked, in a general way, that the subject of heredity is one of profoundest significance in its relation to society. Through its influences the peculiarities and characteristics of families and nations are largely developed and perpetuated. It "is that biological law by which all beings endowed with life tend to repeat themselves in their descendants."[9] It depends upon "an internal principle of vitality" which is so engraven upon every portion of the system before birth, that its influence remains through life, and within certain limits pertains alike to both the physiological and psychological nature. Not that this influence is such, or operates in such a manner, as to repeat itself in any stereotyped form, but rather in an endless variety of forms; while no child resembles its parents in all respects, yet there ever occurs a blending of the characters of both parents, together with a large number of those characteristics which have, for long generations, been interwoven in multiform shades and degrees in ancestors. Passing now from the general to the particular, we find, first, in reference to physiological characteristics and peculiarities, that these tend to repeat themselves more or less directly, so that when they have once appeared, they may, with reason, again be expected. Peculiarities of the fingers and toes, of the hair, the shape of the head, the conformation of the face, and even particular portions of the face, remain for long periods in the same family and nations. The characteristic form of face and nose peculiar to the Jew, is an example in point, and so invariable as to lead to recognition, in spite of the changes and vicissitudes incident to travel and residence during many hundreds of years, under climatic conditions of large diversity, and ofttimes experiences of great and protracted severity. Not only are such peculiarities as may be considered normal transmitted, but also such as are abnormal,--a supernumerary finger or toe, or a mole on some portion of the face or part of the body. A supernumerary finger or toe may be transmitted for at least four generations, though not to every member of the family, and the experiments of Mr. Darwin, with birds, go to show that the tendency to perpetuate such a peculiarity, exhausts itself after a few generations, the type returning to its original character.