So the course of the individual's life is continually being affected by surroundings which compel him to adapt himself to them on pain of extinction if he fails. On the other hand, he is himself, in his own small way, affecting his surroundings and causing _them_ to adapt themselves to _him._ Even the humblest plant takes from the surrounding soil and air what it needs as food and changes it in the process of assimilation, so that the surroundings are, to a slight extent at least, changed by the activity of the plant. And we already have noticed how a plant's insect surroundings have to adapt themselves to the plant. There is reciprocal action, therefore--the surroundings forcing the individual to adapt himself to them, and the individual causing the surroundings to adapt themselves to him. Here we have reached the point where, besides the struggle for existence among the individuals of an abundant, varied, and intense life, there is adaptation among the individuals to their surroundings and of their surroundings to the individuals. * * * We have now to note how with the adaptation goes selection. Set amid these physical and organic surroundings, some helpful, some harmful, the individual has to spend his life in selecting and rejecting what will further or hinder his natural development. He has to reject much, for there is much that will harm him. He has to select a little--for that little is vitally necessary for his upbuilding and maintenance. From among the elements of the soil he has to choose those particular elements that he needs. Thus a plant selects through its roots from the elements of the soil, and through its leaves from the elements of the air, those elements and in those quantities that it needs for nourishment and growth. But it has also, by means of thorns or poison juices or other device, to protect itself from being itself selected by some animal for that animal's own nourishment and growth. So the individual is constantly selecting, and is as constantly on the guard against being selected. The principle of selection among the abundant and varied life is in continual operation. And unless he selects wisely he will not survive; for he will either have insufficient to live on or else have what is harmful to his life. Nor will he survive unless he is able to fend off those who would select him for their own maintenance. There is selection everywhere--selection _by_ the individual and selection _of_ the individual by surrounding neighbours and circumstances. * * *