The outcropping of ancestral types of mentality is observed to underlie many of the manifestations of vice and crime. These ancestral types or traits may revert farther back even than the savage progenitors of civilised man, and approximate those of the lower animals who, in their turn, stand behind the savage in the line of descent. This "reversion to older and lower types," or "breeding back," is important, because it is the source of much crime--the origin of very many "Bottom Dogs," as we shall see. But at present we need only notice that heredity, or breed, reaches back through immense distances of time; so that a man inherits not only from savage ancestors, but also from the brutes. And man has no power to _choose_ his breed, has no choice of ancestors, but must take the qualities of body and mind they hand down to him, be those qualities good or bad. Descent, or breed, does not work regularly. Any trait of any ancestor, beast or man, near or remote, may crop up suddenly in any new generation. A child may bear little likeness to its father or mother: it may be more like its great-grandfather, its uncle, or its aunt. It is as though every dead fore-parent back to the dimmest horizon of time, were liable to put a ghostly finger in the pie, to mend or mar it. Let us now use a simple illustration of the workings of heredity, variation, and atavism, or breeding back. There is no need to trouble ourselves with the scientific explanations. What we have to understand is that children inherit qualities from their ancestors; that children vary from their ancestors and from each other; and that old types or old qualities may crop out suddenly and unexpectedly in a new generation. Knowing, as we do, that children inherit from their parents and fore-parents, the rest may be made, quite plain without a single scientific word. In our illustration we will take for parents and children bottles, and for hereditary qualities beads of different colours. THE MYSTERY OF DESCENT MADE EASY Now, take a bottle of red beads, and call it male. Take a bottle of blue beads, and call it female. From each bottle take a portion of beads; mix them in a third bottle and call it "child." We have now a child of a red father and a blue mother; and we find that this child is not all red, nor all blue, but part red and part blue. It is like the father, for it has red beads; it is like the mother, for it has blue beads. It is unlike the father, for the father has no blue, and it is unlike the mother, for the mother has no red. Here we have a simple illustration of "heredity" and "variation." Now, could we blame the "child" bottle for having red and blue beads in it; or could we blame the "child" bottle for having no yellow and no green beads in it? But that is an example of a simple mixture of two ancestral strains. We have to do with mixtures of millions of strains. Let us carry our illustration forward another generation.