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Haeckel, Ernst Heinrich (1834–1919)


Ernst Heinrich Haeckel, the German zoologist and monist philosopher, was born in Potsdam. He studied medicine and science at Würzburg, Berlin, and Vienna with such authorities as Johannes Müller, Rudolf Virchow, and R. A. Kölliker. After practicing medicine for a short time, he went to the University of Jena in 1862 to teach zoology.

Haeckel was the first noted German biologist to grant enthusiastic acceptance to organic evolution, and Charles Darwin gave him credit for propagating the theory of evolution in Germany. His views were the source of considerable controversy in biology, philosophy, and religion. He battled with his colleagues about their early hostility to Darwin's theory and their reluctance to include man and his consciousness in the evolutionary process. His dislike of the power of the church in social and political matters and his liberal opposition to Otto von Bismarck and other political figures resulted in many controversies; his rejection of free will, immortality, and the personality of God also antagonized many. Haeckel's achievements in zoology brought him academic offers from famous institutions, but he chose to remain at Jena, partly because of the academic freedom he found there.

His interests were broad; he published travel works and illustrated some of his own scientific essays. He founded the Monistic League to propagate his religious views. He had considerable popular success in science and was prominent in the movement to enlighten humankind about scientific developments.

Scientific Contributions

In biology Haeckel helped to publicize and promulgate what he called the "biogenetic law": "Ontogenesis is a brief and rapid recapitulation of phylogenesis, determined by the physiological functions of heredity (generation) and adaptation (maintenance)" (The Riddle of the Universe, New York, 1900, p. 81). He was a pioneer in drawing up genealogical schemata of the relationships between various orders of animals. Many of his major groupings are still accepted, although the finer divisions have undergone much revision. He was convinced of the essential unity of organic and inorganic nature, and argued that the simplest protoplasmic substances arose from inorganic carbonates through spontaneous generation. Individual primitive organisms, which Haeckel termed "monera," were differentiated out of these protoplasmic compounds. Haeckel believed that to reject this kind of spontaneous generation was tantamount to accepting a miraculous origin of life.

His theory of gastraea also received much attention. Haeckel argued that the entire animal world is made up of two groups: primitive unicellular animals, the protozoa, and multicellular animals with complex tissues, the metazoa. Haeckel believed that all the metazoa evolved, in accord with his biogenetic law, from one simple, long-extinct form, the gastraea. Although this theory of evolution from gastraea is no longer accepted, it influenced embryological research for nearly half a century.

Doctrine of Substance

Haeckel's conviction on the great importance of organic evolution led him into many other fields. His Die Welträthsel (Bonn, 1899; English translation by Joseph McCabe, The Riddle of the Universe ) became a best-seller. The title derived from Emil Du Bois-Reymond's 1880 address to the Berlin Academy of Sciences on seven "world enigmas" (the nature of matter and force, the origin of motion, the origin of life, the order in nature, the origin of simple sensation and consciousness, rational thought and speech, and freedom of the will). Haeckel believed that his monistic outlook could resolve these problems, and others, leaving one "comprehensive riddle," the problem of substance. He insisted upon the essential unity of all substance, but also insisted that the "real character" of substance was as little understood as in the days of Anaximander and Empedocles. Indeed, it became "more mysterious and enigmatic" as more and more became known about its attributes and their evolutionary forms. Haeckel was especially opposed to theological dualism, but he also carefully distinguished his view from both materialistic and idealistic monisms.

Haeckel construed materialism as holding that atoms are "dead," and are moved only by external forces. He maintained instead that both matter and ether possess sensation and will in the lowest grade. They experience a dislike of strain, and struggle against it, and a liking of "condensation," for which they strive. Haeckel denied the existence of empty space and of action at a distance. Those parts of space not occupied with ponderable atoms are filled with ether; action is either the result of immediate contact or occurs through the mediation of ether.

On the other hand, Haeckel rejected any attempt to regard the world as immaterial or nonnatural. Infinitely extended matter and sensitive and thinking spirit, or energy, are two fundamental attributes of the all-embracing universal substance. Every living cell has psychic properties, and multicellular organisms have as their psychic functions the totality of the psychic properties of their parts. Although Haeckel insisted that his view of substance was Spinoza-like rather than materialistic, many of his specific views are similar to those of nineteenth-century materialism. His confidence that "consciousness, thought, and speculation" are "functions of the ganglionic cells of the cortex of the brain," his "hard" determinism, his mechanism, his complete rejection of the supernatural, and his enthusiasm for science all inclined his contemporaries to classify him as a materialist.

Haeckel, then, saw the world as an eternal evolution of substance, and man as part of that evolution. The "law of substance," a law of mechanical causality, established "the eternal persistence of matter and force, their unvarying constancy throughout the entire universe" (The Riddle of the Universe, p. 4). He regarded the laws of the conservation of energy and the conservation of matter as inseparable and as parts of his law of substance. Haeckel referred to "great eternal iron laws," and rejected all teleological views. The appearance of design in the world is a consequence of natural selection rather than of the action of a purposive agency.

Although Haeckel often emphasized the tentative nature of scientific conclusions and the necessity for the modification and improvement of hypotheses, on some issues he assumed the finality of certain scientific propositions, including many rejected today. He made this assumption most frequently in his polemics against the philosophic and religious views that he regarded as incompatible with science. Haeckel did not generally consider in detail the technical problems philosophers were debating, but tended rather to attack or to defend the conclusions of technical philosophers on the basis of the scientific results of his day and extrapolations from them.

Theory of Knowledge

Despite his insistence that much of philosophy was far too speculative and a priori, Haeckel held that both empiricism and rationalism are necessary to develop satisfactory knowledge. Although he was hostile to "pure metaphysics," he was also critical of those who advocated a "pure empiricism." The opposition between experimental science and philosophy must and can be overcome.

Haeckel held that the thing-in-itself lying behind knowable phenomena is unknown. He suggested that we need not trouble about this situation; we have no means for investigating the thing-in-itself, and are not even certain it exists. The only genuine knowledge is knowledge of nature, and it consists of "presentations" (combinations of sense impressions in the knowing subject) corresponding to external things. Comparative and critical observation tells us that normally the impressions received by the brain and sense organs from the outer world are the same for all rational people, and that normally the same presentations are formed. Those presentations are true that correspond to the knowable aspects of things, even though things-in-themselves" cannot be reached.

Haeckel's views on knowledge were closely connected to biological findings. He argued that the human sense activity, which forms the beginning of all knowledge, was slowly and gradually evolved from the other primates. The sense organs of all primates are structurally similar, and Haeckel insisted that these organs also function similarly, in a way describable by the same chemicophysical laws. The rod-shaped cells in the retina, the auditory cells in the ear, the olfactory cells in the nose, and the taste cells on the tongue were evolved from simple, undifferentiated cells of the skin. Invoking his biogenetic law, Haeckel concluded that man's higher sense organs were derived from the epidermis of lower animals. Our sense impressions are associated in the cortex of the brain so that isolated elements are united into integrated wholes. Haeckel called these integrated presentations "faith in the broad sense," because they go beyond our sense impressions. In this sense, science requires faith in the construction of both hypotheses and unifying theories. (In the main, Haeckel used "theory" to refer to hypotheses about a common cause for diverse phenomena.) However, he rejected religious faith, which he termed "faith in the narrower sense." He insisted that religious belief always means a belief in miracles and thus contradicts the "natural faith of reason." Even religious liberals, he contended, are forced into the acceptance of superstition, and their faith is no less irrational than the "crude spirit-faith of primitive fetichism."


Haeckel attempted a scientific account of the soul. He regarded it as a natural phenomenon, so that psychology was a natural science, a part of physiology. Psychology was the "foundation and the postulate" of all the sciences, since knowledge of nature is "part of the life of the soul." The great difficulty in establishing a naturalistic psychology is that such a science presupposes a thorough knowledge of the human organism, especially the brain. Haeckel deplored the lack of biological training of the psychologists of his time. He insisted that psychic processes, like all others, are subject to the law of substance, and held that the prevalence of mind-body dualisms in psychology has led to a greater confusion of ideas there than in any other department of knowledge. Yet Haeckel did not insist on a nonintrospective psychology; he described the introspective method as "extremely valuable and indispensable." But it had to be supplemented by experimental methods.

Haeckel regarded consciousness as the "central mystery of psychology," and the citadel of all mystical and dualistic errors. He insisted that consciousness is a natural phenomenon, dependent upon a material substratum. He suggested that consciousness can perhaps best be conceived as "internal perception" and can be compared to the action of a mirror. The chief difficulty in the way of a scientific understanding of consciousness is that the subject and the object of knowledge are one and the same; our only source of knowledge of consciousness is consciousness itself. We can therefore only know the consciousness of others by comparing it with our own. This works rather well when the comparison is made between normal people, but the analogy may break down badly when a comparison is made between the normal and the abnormal, or between different evolutionary levels. However, the difference between the consciousness of humans and of other animals is a difference of degree only, not of kind. Haeckel thought it probable that consciousness arises with the centralization of the nervous system, and that the lower classes of animals lack that faculty. The province of unconscious psychic actions, reflex action, for example, is more extensive than that of conscious ones, but the two areas are closely connected.

The consciousness of man and of other mammals biologically close to man is changeable and is modified by both internal and external causes. Consciousness is dependent upon the normal development of certain organs and gradually develops in the child as those organs develop. Despite Haeckel's use of a "faculties" terminology, his views on psychology are often similar to those of recent functionalists.

Attack on Traditional Religion

Haeckel's attack on supernatural religions had many facets. He unequivocally rejected revelation and theological faith. He was outspoken in combating the superstitions associated with the world's great religions. He scathingly attacked the influence of the church as an institution in politics and education. Indeed, he frequently coupled these problems, holding that the German government would not improve until it was free from church influence and its citizens received a better, more scientific, education. Haeckel even claimed that such questions as whether a monarchy is preferable to a republic and whether the constitution should be aristocratic or democratic are subordinate to the "supreme question": Shall the government be secular or dominated by the clergy? Haeckel was no respecter of religious heroes, prominent clerics, sacred myths, or widely held dogma. He tried to show that theological beliefs are incompatible with scientific data, unreasonable, or merely dogmatic.

Haeckel's admiration for the views of Benedict Spinoza and Johann Wolfgang von Goethe and his belief that humankind's ethical aspirations needed some support led him to advocate a monistic religion. "The ethical craving of our emotion is satisfied by monism no less than the logical demand for causality on the part of reason." He had great respect for the ethical values of primitive Christianity, and felt that Christianity had been so influential in the social and political movements of civilized history that "we must appeal as much as possible to its existing institutions in the establishment of our monistic religion" (The Riddle of the Universe, p. 336). He maintained, therefore, that he sought a rational reformation, rather than a revolution, in religion. However, the extent of his criticisms of Christianity appear to be revolutionary.

Haeckel wanted to give rational support to the true, the good, and the beautiful, and he considered the relation of that trinity to prevailing Christian notions. Truth is to be found in the study of nature by means of critical observation and reflection, and hence revelation must be rejected. However, what "we call virtue, in our monistic religion coincides for the most part with the Christian idea of virtue," especially the Christianity of the first three centuries. Charity, toleration, compassion, and assistance are humanistic as well as Christian precepts, and are to be emphasized in the monistic religion.

On the other hand, Haeckel maintained that early Christianity preached the valuelessness of this-worldly things, because this life was merely a preparation for eternity. Hence the beautiful was of little consequence. Haeckel was especially interested in art forms in nature and believed that the microscope had newly aroused our aesthetic sense.

All forms of theism are to be opposed. A pantheism that identifies God and substance is necessarily "the world-system of the modern scientist." All scientists who think theism can be reconciled with science are, in Haeckel's view, either dishonest, or confused, or victims of sophistry. If atheism is construed as a denial of the existence of a personal and extramundane god or gods, then Haeckel agreed with Arthur Schopenhauer's remark that pantheism is only a polite form of atheism. In short, Haeckel's criticism of traditional religions was that their doctrines are often intellectually wrong; that they generate unrealistic hopes; and that the social, political, and educational consequences of supernaturalism are malignant. Haeckel's criticisms, especially of Roman Catholicism, are often strongly worded. Thus he wrote that the obligatory celibacy of the clergy, auricular confession, and the sale of indulgences were designed for the purposes of strengthening the rule of the church over the "credulous masses and making as much material profit as possible out of them."

Ethics and Social Views

In ethics, Haeckel felt that traditional theories often either emphasize altruism too much (as in the case of many religious views) or emphasize egoism too much (hedonisms). He held that there should be an "equal emphasis" on self-love and love of one's neighbor. The "highest aim of all ethics" is to reestablish a "natural equality" of egoism and altruism. Along with this should go an emphasis on the body as well as the soul; an emphasis on fair treatment of animals as well as humans. Haeckel believed that a recognition of human evolution would incline us to be more sympathetic to animals, and that Christian attitudes easily lead to cruelty toward animals. Haeckel regarded the family as the foundation of society and as a necessity for humanity as well as for the higher social animals, whereas Christianity, he believed, tends to disparage the family as a this-worldly phenomenon. Haeckel also opposed the tendency that he found in Christianity to make woman subordinate to man and to regard sexual intercourse as "unclean." He was especially hostile to the hypocrisy he believed is often found in the church toward sex.

Haeckel was much interested in social reform, holding that progress is a law of nature. He compared the rapid progress made in the natural sciences with the lack of progress in government, the administration of justice, education, and social and moral organization. He gave special attention to justice. He believed that students of jurisprudence need much more education in science than they usually receive, and that their knowledge of human nature is sadly deficient. Politicians too make practical decisions of great import with no scientific grounding in the appropriate areas. He also decried the many impediments to free inquiry, whether they stem from political reaction or from theological superstition. He was highly optimistic about the consequences of an improved system of education.

Many of Haeckel's views that caused violent disputes in the past are today widely accepted by educated people. Much of the antagonism toward him was centered on his insistence that man is a part of nature and in the evolutionary stream. Although large portions of the scientific part of Haeckel's worldview have since been rejected, much is still regarded as sound. His views on religion would still be challenged by many; some, of course, find them mild.

See also Altruism; Darwin, Charles Robert; Empiricism; Evolutionary Theory; Goethe, Johann Wolfgang von; Hedonism; Justice; Materialism; Progress, The Idea of; Psychology; Rationalism; Schopenhauer, Arthur; Spinoza, Benedict (Baruch) de.


additional works by haeckel

Generelle Morphologie der Organismen. 2 vols. Berlin: G. Reimer, 1866.

Natürliche Schöpfungsgeschichte. Berlin, 1868. Translated into English by E. R. Lankester as The History of Creation. London: H.S. King, 1876.

Anthropogenie. Leipzig, 1874. Translated into English by Joseph McCabe as The Evolution of Man. New York: Putnam's Sons, 1910.

Freie Wissenschaft und freie Lehre. Stuttgart: E. Schweizerbart, 1878. Translated into English as Freedom in Science and Teaching. New York: D. Appleton, 1879.

Der Monismus als Band zwischen Religion und Wissenschaft. Bonn: E. Strauss, 1893. Translated into English by J. Gilchrist as Monism as Connecting Religion and Science: The Confession of Faith of a Man of Science. London: A. and C. Black, 1895.

Die Lebenswunder. Stuttgart: A. Kröner, 1904. Translated into English by Joseph McCabe as The Wonders of Life. New York: Harper, 1905.

Der Kampf um den Entwickelungs-Gedanken. Berlin, 1905. Translated into English by Joseph McCabe as Last Words on Evolution. London: A. Owen, 1906.

works on haeckel

Bölsche, Wilhelm. Ernst Haeckel: Ein Lebensbild. Leipzig: H. Seeman, 1900. Translated into English by Joseph McCabe as Haeckel: His Life and Work. London: T.F. Unwin, 1906. Contains a useful bibliography to 1900 as well as detailed accounts of Haeckel's life and work. McCabe added a supplementary chapter, "The Crowning Years," which gives an account of the controversies in which Haeckel engaged after the publication of The Riddle of the Universe.

Merz, J. T. A History of European Thought in the Nineteenth Century. Edinburgh: Blackwood, 1903. Treats Haeckel and his contemporaries in some detail.

Perry, R. B. Present Philosophical Tendencies. New York: Longmans, Green, 1912. Gives a brief account of Haeckel and his contemporaries and also discusses the leading issues that engaged their interest.

Schmidt, Heinrich. Ernst Haeckel, Leben und Werke. Berlin, 1926.

Rollo Handy (1967)

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