But this recognition of distinct species is, from the point of view of the study of Nature, only a preliminary to the question, "How did these species come about? How is it that there are so many species, some very like one another, forming genera, and these genera grouped into related families, these into larger groups, and so on, like the branches of a family tree?" The answer to these questions given by Linnæus was: "There are just so many species as the Infinite Being created at the beginning of things, and they have continued to propagate themselves unchanged ever since." The answer which we give to-day is that the appearance of a huge family tree which our classification of animals takes is due to the simple fact that it really is neither more nor less than a family tree or pedigree–the "tree of life," of which the green leaves and buds are the existing species. Further, we hold that the existing species of a genus have "come into existence" by natural birth from one ancestral species, its offspring having slightly varied (we are all familiar with this individual variation in our own species, in dogs, cats, trees, and shrubs), and that the varieties have wandered apart and become continuously emphasized and selected for survival by their fitness or suitability to the changed conditions around each of them. Meanwhile a natural destruction, or failure of intermediate forms to survive, has gone on. CHAPTER IX SPECIES IN THE MAKING A series of important conceptions are implied in the word "species," as used by naturalists. Some of these we have noted in the last chapter. There is first, as a starting-point, the conception that a species is a number or company of individuals, all closely and clearly alike (though presenting some minor individual variations), and capable of sharp separation by certain "characters" from other similar groups or companies. Then follows the addition (2) that the species is constant if the conditions of life are not changed, or but little changed, and that year after year it reproduces itself without change. It has a certain stability (but not permanent immutability) greater in some species than in others. Next we find (3) that the species constitutes a group of individuals which have descended by natural breeding from common parents, not differing greatly from the present individuals. They are, in fact, one "stock." Then (4) that the species is a group, the individuals of which pair with one another in breeding, but do not pair with the individuals of another species, and that this is due to various peculiar and inherent chemical, physiological and (in higher animals) psychological characteristics of the species.