Since we have learned to study the development of human life as we study the evolution of species throughout the animal kingdom, some peculiar phenomena which have puzzled the philosopher and moralist for so long, begin to show themselves in a new light. We begin to see that, so far from being inscrutable problems, requiring another life to explain, these sorrows and perplexities of our lives are but the natural results of natural causes, and that, as soon as we ascertain the causes, we can do much to remove them.In spite of the power of the individual will to struggle against conditions, to resist them for a while, and sometimes to overcome them, it remains true that the human creature is affected by his environment, as is every other living thing. The power of the individual will to resist natural law is well proven by the life and death of the ascetic. In any one of those suicidal martyrs may be seen the will, misdirected by the ill-informed intelligence, forcing the body to defy every natural impulse, -even to the door of death, and through it.But, while these exceptions show what the human will can do, the general course of life shows the inexorable effect of conditions upon humanity. Of these conditions we share with other living things the environment of the material universe. We are affected by climate and locality, by physical, chemical, electrical forces, as are all animals and plants. With the animals, we farther share the effect of our own activity, the reactionary force of exercise. What we do, as well as what is done to us, makes us what we are. But, beyond these forces, we come under the effect of a third set of conditions peculiar to our human status; namely, social conditions. In the organic interchanges which constitute social life, we are affected by each other to a degree beyond what is found even among the most gregarious of animals. This third factor, the social environment, is of enormous force as a modifier of human life. Throughout all these environing conditions, those which affect us through our economic necessities are most marked in their influence.Without touching yet upon the influence of the social factors, treating the human being merely as an individual animal, we see that he is modified most by his economic conditions, as is every other animal. Differ as they may in color and size, in strength and speed, in minor adaptation to minor conditions, all animals that live on grass have distinctive traits in common, and all animals that eat flesh have distinctive traits in common, -so distinctive and so common that it is by teeth, by nutritive apparatus in general, that they are classified, rather than by means of defence or locomotion. The food supply of the animal is the largest passive factor in his development; the processes by which he obtains his food supply, the largest active factor in his development. It is these activities, the incessant repetition of the exertions by which he is fed, which most modify his structure and develope his functions. The sheep, the cow, the deer, differ in their adaptation to the weather, their locomotive ability, their means of defence; but they agree in main characteristics, because of their common method of nutritio