of life is sharply defined physiologically by its metabolism and chemically by its plasm; but when we come to study the question of abiogenesis (chapter xv.) we shall find that this division is not absolute, and that organic life has been evolved from inorganic nature. Moreover, biology and abiology are connected branches of cosmology, or the science of the world.
While the idea of biology is now usually taken in this broad sense in most scientific works and made to embrace the whole of living nature, we often find (especially in Germany) a narrower application of the term. Many authors (mostly physiologists) understand by it a section of physiology—namely, the science of the relations of living organisms to the external world, their habitat, customs, enemies, parasites, etc. I proposed long ago to call this special part of biology œcology (the science of home-relations), or bionomy. Twenty years later others suggested the name of ethology. To call this special study any longer biology in the narrower sense is very undesirable, because it is the only name we have for the totality of the organic sciences.
Like every other science, biology has a general and a special part. General biology contains general information about living nature; this is the subject of the present study of the wonders of life. We might also describe it as biological philosophy, since the aim of true philosophy must be the comprehensive survey and rational interpretation of all the general results of scientific research. The innumerable discoveries of detailed facts which observation and experiment give us, and which are combined into a general view of life in philosophy, form the subject of empirical science. As the latter, on the side of the organic world, or as empirical biology, forms the first object of the science of life, and seeks to effect in the system of nature a logical arrangement and summary grouping of the countless special forms of life, this special biology is often wrongly called the science of classification.
The first comprehensive attempt to reduce to order and unity the ample biological material which systematic research had accumulated in the eighteenth century was made by what we call "the older natural philosophy" at the beginning of the nineteenth century. Reinhold Treviranus (of Bremen) had made a suggestive effort to accomplish this difficult task on monistic principles in his Biology, or Philosophy of Living Nature (1802). Special importance attaches to the year 1809, in which Jean Lamarck (of Paris) published his Philosophie Zoologique, and Lorentz Oken (of Jena) his Manual of Natural Philosophy. I have fully appreciated the service of Lamarck, the founder of the theory of descent, in my earlier writings. I have also recognized the great merit of Lorentz Oken, who not only aroused a very wide interest in this science by his General Natural History, but also put forward some general observations of great value. His "infamous" theory of a primitive slime, and the development of infusoria out of it, is merely the fundamental idea of the theory of protoplasm and the cell which was long afterwards fully recognized. These and other services of the older natural philosophy were partly ignored and partly overlooked, because they went far beyond the scientific horizon of the time, and their authors to an extent lost themselves in airy and fantastic speculations. The more scientists confined themselves in the following half-century to empirical work and the observation and description of separate facts, the more it became the fashion to look down on all "natural philosophy." The most paradoxical feature of the situation was that purely speculative philosophy and idealist metaphysics had a great run at the same time, and their castles in the air, utterly destitute of biological foundation, were much admired.
The magnificent reform of biology which Darwin initiated in 1859 by his epoch-making Origin of Species gave a fresh impulse to natural philosophy. As this work not only used the rich collection of facts already made in proof of the theory of descent, but gave it a new foundation in the theory of selection (Darwinism properly so called), everything seemed to call for the embodiment of the new conception of nature in a monistic system. I made the first effort to do this in my General Morphology (1866). As this found few supporters among my colleagues, I undertook in my History of Creation (1868) to make the chief points of the system accessible to the general reader. The remarkable success of this book (a tenth edition of it appearing in 1902) emboldened me at the end of the nineteenth century to state the general principles of my monistic philosophy in my Riddle of the Universe. About the same time (1899) there appeared the work of the Kiel botanist, Johannes Reinke, The World as Reality; and two years afterwards he followed it up with a supplementary volume, Introduction to Theoretic Biology. As Reinke treats the general problems of natural philosophy from a purely mystic and dualistic point of view, his ideas are diametrically opposed to my monistic and naturalistic principles.
The history of philosophy describes for us the infinite variety of ideas that men have formulated during the last three thousand years on the nature of the world and its phenomena. Überweg has given us, in his excellent History of Philosophy, a thorough and impartial account of these various systems. Fritz Schultze has published a clear and compendious "tabulated outline" of them in thirty tables in his genealogical tree of philosophy, and at the same time shown the phylogeny of ideas. When we survey this enormous mass of philosophic systems from the point of view of general biology, we find that we can divide them into two main groups. The first and smaller group contains the monistic philosophy, which traces all the phenomena of existence to one single common principle. The second and larger group, to which most philosophic systems belong, constitutes the dualistic philosophy, according to which there are two totally distinct principles in the universe. These are sometimes expressed as God and the world, sometimes as the spiritual world and material world, sometimes as mind and matter, and so on. In my opinion, this antithesis of monism and dualism is the most important in the whole history of philosophy. All other systems are only variations of one or the other of these, or a more or less obscure combination of the two.
The form of monism which I take to be the most complete expression of the general truth, and which I have advocated in my writings for thirty-eight years, is now generally called hylozoism. This expresses the fact that all substance has two fundamental attributes; as matter (hyle) it occupies space, and as force or energy it is endowed with sensation (cf. chapter xix.). Spinoza, who gave the most perfect expression to this idea in his "philosophy of identity," and most clearly treated the notion of substance (as the all-embracing essence of the world), clothes it with two general attributes—extension and thought. Extension is identical with real space, and thought with (unconscious) sensation. The latter must not be confused with conscious human thought; intelligence is not found in substance, but is a special property of the higher animals and man. Spinoza identifies his substance with nature and God, and his system is accordingly called pantheism; but it must be understood that he rejects the anthropomorphic, personal idea of deity.
A good deal of the infinite confusion that characterizes the conflicts of philosophers over their systems is due to the obscurity and ambiguity of many of their fundamental ideas. The words "substance" and "God," "soul" and "spirit," "sensation" and "matter," are used in the most different and changing senses. This is especially true of the word "materialism," which is often wrongly taken to be synonymous with monism. The moral bias of idealism against practical materialism (or pure selfishness and sensualism) is forthwith transferred to theoretical materialism, which has nothing to do with it; and the strictures which are justly urged against the one are most unjustifiably applied to the other. Hence it is important to distinguish very carefully between these two meanings of materialism.
Theoretical materialism (or hylonism), as a realistic and monistic philosophy, is right in so far as it conceives matter and force to be inseparably connected, and denies the existence of immaterial forces. But it is wrong when it denies all sensation to matter, and regards actual energy as a function of dead matter. Thus, in ancient times Democritus and Lucretius traced all phenomena to the movements of dead atoms, as did also Holbach and Lamettrie in the eighteenth century. This view is held to-day by most chemists and physicists. They regard gravitation and chemical affinity as a mere mechanical movement of atoms, and this, in turn, as the general source of all phenomena; but they will not allow that these movements necessarily presuppose a kind of (unconscious) sensation. In conversation with distinguished physicists and chemists I have often found that they will not hear a word about a "soul" in the atom. In my opinion, however, this must necessarily be assumed to explain the simplest physical and chemical processes. Naturally I am not thinking of anything like the elaborate psychic action of man and the