The publication of the present work on The Wonders of Life has been occasioned by the success of The Riddle of the Universe, which I wrote five years ago. Within a few months of the issue of this study of the monistic philosophy, in the autumn of 1899, ten thousand copies were sold. Moreover, the publisher having been solicited on many sides to issue a popular edition of the work, more than a hundred thousand copies of this were sold within a year.[1] This extraordinary and—as far as I was concerned—unexpected success of a philosophical work which was by no means light reading, and which had no particular charm of presentation, affords ample proof of the intense interest taken by even the general reader in the object of the work—the construction of a rational and solid philosophy of life.

Naturally, the clear opposition of my monistic philosophy, based as it was on the most advanced and sound scientific knowledge, to the conventional ideas and to an outworn "revelation," led to the publication of a vast number of criticisms and attacks. During the first twelve months more than a hundred reviews and a dozen large pamphlets appeared, full of the most contradictory strictures and the most curious observations. One of the ablest of my pupils, Heinrich Schmidt, gave a summary and criticism of them in his Der Kampf um die WeltrÄthsel, in the autumn of 1900. However, the literary struggle went on to assume gigantic proportions when twelve different translations of the Riddle appeared, and led to an ever-increasing agitation in every educated country of the Old and the New World.

I gave a brief reply to the chief of these attacks in April, 1903, in the appendix to the popular edition of the Riddle. It would be useless to go further into this controversy and meet the many attacks that have since been made. It is a question here of that profound and irreconcilable opposition between knowledge and faith, between a real knowledge of nature and an alleged "revelation," which has occupied the thoughtful and inquiring mind for thousands of years. I base my monistic philosophy exclusively on the convictions which I have gained during fifty years' close and indefatigable study of nature and its harmonious working. My dualistic opponents grant only a restricted value to these experiences; they would subordinate them to the fantastic ideas which they have reached by faith in a supernatural world of spirits. An honest and impartial consideration of this palpable contradiction discovers it to be irreconcilable—either science and experience, or faith and revelation!

For this reason I do not propose to make any further reply to the opponents of The Riddle of the Universe, and I am still less disposed to take up the personal attacks which some of my critics have thought fit to make on me. In the course of this controversy I have grown painfully familiar with the means with which it is sought to silence the detested free-thinker—misrepresentation, sophistry, calumny, and denunciation. "Critical" philosophers of the modern Kantist school vie in this with orthodox theologians. What I have said in this connection of the theologian Loofs, of Halle, the philologist Dennert, of Godesberg, and the metaphysician Paulsen, of Berlin, in the appendix to the cheap German edition of the Riddle, applies equally to many other opponents of the same type. These heated partisans may continue to attack and calumniate my person as they will; they will not hurt the sacred cause of truth in which I labor.

Much more interesting to me than these attacks were the innumerable letters which I have received from thoughtful readers of the Riddle during the last five years, and particularly since the appearance of a popular edition. Of these I have already received more than five thousand. At first I conscientiously replied to each of these correspondents, but I had at length to content myself with sending a printed slip with the intimation that my time and strength did not permit me to make an adequate reply. However, though this correspondence was very exacting, it afforded a very welcome proof of the lively sympathy of a large number of readers with the aim of the monistic philosophy, and a very interesting insight into the mental attitude of the most varied classes of readers. I especially noticed that the same remarks and questions occurred in many of these five thousand letters, very often expressed in the same terms. Most of the inquiries related to biological questions, which I had cursorily and inadequately touched both in The Riddle of the Universe and The History of Creation. The natural desire to remedy these deficiencies of my earlier writings and give a general reply to my interrogators was the immediate cause of the writing of the present work on The Wonders of Life.

I was confirmed in this design by the circumstance that another scientist, the botanist Johannes Reinke, of Kiel, had published two works in which he had treated the general problems of natural philosophy, especially of biology, from a purely dualistic and teleological point of view; these works were his Die Welt als That (1899) and Einleitung in die theoretische Biologie (1902). As both these works are well written and present the principles of dualism and teleology with admirable consistency—as far as this is possible—it seemed to me that it was desirable to give a thorough exposition of my own monistic and causative system.

Hence the present work on the wonders of life is, as the title indicates, a supplementary volume to The Riddle of the Universe. While the latter undertook to make a comprehensive survey of the general questions of science—as cosmological problems—in the light of the monistic philosophy, the present volume is confined to the realm of organic science, or the science of life. It seeks to deal connectedly with the general problems of biology, in strict accord with the monistic and mechanical principles which I laid down in 1866 in my General Morphology. In this I laid special stress on the universality of the law of substance and the substantial unity of nature, which I have further treated in the second and fourteenth chapters of The Riddle of the Universe.

The arrangement of the vast material for this study of the wonders of life has been modelled on that of the Riddle. I have retained the division into larger and smaller sections and the synopses of the various chapters. Thus the whole biological content falls into four sections and twenty chapters. I should much have liked to add illustrations in many parts of the text to make the subject plainer, especially as regards chapters vii., viii., xi., and xvi.; but this would have led to a considerable increase in the size and price of the book. Moreover, there are now many illustrated works which will help the reader to go more fully into the various sections of the study. Among others, my History of Creation (English translation) and Evolution of Man (English translation now in course of preparation) will be found helpful in this way. The German reader will also find many illustrations to elucidate the text of this book in my recently completed work, Kunstformen der Natur (10 parts, with 100 tables, 1899-1904).

I had said, in the preface to The Riddle of the Universe in 1899, that I proposed to close my study of the monistic system with that work, and that "I am wholly a child of the nineteenth century, and with its close I draw the line under my life's work." If I now seem to run counter to this observation, I beg the reader to consider that this work on the wonders of life is a necessary supplement to the widely circulated Riddle of the Universe, and that I felt bound to write it in response to the inquiries of so many of my readers. In this second work, as in the earlier one, I make no pretension to give the reader a comprehensive statement of my monistic philosophy in the full maturity it has reached—for me personally, at least—at the close of the nineteenth century. A subjective theory of the world such as this can, naturally, never hope to have a complete objective validity. My knowledge is incomplete, like that of all other men. Hence, even in this "biological sketch-book," I can only offer studies of unequal value and incomplete workmanship. There still remains the great design of embracing all the exuberant phenomena of organic life in one general scheme and explaining all the wonders of life from the monistic point of view, as forms of one great harmoniously working universe—whether you call this Nature or Cosmos, World or God.

The twenty chapters of The Wonders of Life were written uninterruptedly in the course of four months which I spent at Rapallo, on the shore of the blue Mediterranean. The quiet life in this tiny coast-town of the Italian Riviera gave me leisure to weigh again all the views on organic life which I had formed by many-sided experience of life and learning since the beginning of my academic studies (1852) and my teaching at Jena (1861). To this I was stimulated by the constant sight of the blue Mediterranean, the countless inhabitants of which had, for fifty years, afforded such ample material for my biological studies; and my solitary walks in the wild gorges of the Ligurian Apennines, and the moving spectacle of its forest-crowned mountain altars, inspired me with a feeling of the unity of living nature—a feeling that only too easily fades away in the study of detail in the laboratory. On the other hand, such a situation did not allow a comprehensive survey of the boundless literature which has been evoked by the immense advances in every branch of biology. However, the present work is not intended to be a systematic manual of general biology. In the revision of the text, on which I was engaged during the summer at Jena, I had to restrict myself to occasional additions and improvements. In this I had the assistance of my worthy pupil, Dr. Heinrich Schmidt, to whom also I am indebted for the careful revision of the proofs.

When I completed my seventieth year at Rapallo, on February 16th, I was overwhelmed with a mass of congratulations, letters, telegrams, flowers, and other gifts, most of which came from unknown readers of The Riddle of the Universe in all parts of the world. If my thanks have not yet reached any of them, I beg to tender them in these lines. But I should be especially gratified if they would regard this work on the wonders of life as an expression of my thanks, and as a literary gift in return. May my readers be moved by it to penetrate deeper and deeper into the glorious work of Nature, and to reach the insight of our greatest German natural philosopher, Goethe:

"What greater thing in life can man achieve
Than that God-Nature be revealed to him?"

Ernst Haeckel.

Jena, June 17, 1904.

THE WONDERS OF LIFE