HAECKEL, ERNST HEINRICH German biologist, was born at Potsdam on Feb. 16, 1834. He studied medicine and science at Wiirzburg, Berlin and Vienna under such men as Johannes Muller, R. Virchow and R. A. Kolliker. In 1862 he became professor of comparative anatomy and director of the zoological institute at Jena, where a chair of zoology was cre ated for him in 1865. At Jena he spent his life, with the exception of the time devoted to various tours. As a field naturalist Haeckel's extraordinary power and industry were displayed in his publica tions on Radiolaria (1862), Siphonophora (1869), Monera (187o) and Calcareous Sponges (1872), as well as several Challenger reports, viz. Deep-Sea Medusae (1881), Siphonophora (1888), Deep-Sea Keratosa (1889) and Radiolaria (1887).
Meanwhile he had become the first German biologist to give a wholehearted adherence to the doctrine of organic evolution, and Darwin himself believed that Haeckel's enthusiastic propagandism was the chief factor of the success of the doctrine in Germany. His General Morphology (1866) was a suggestive attempt to work out the practical application of evolution to its final results. Natur liche Schopfungsgeschichte (1867, loth ed. 19(32, Eng. trans. 1892) laid particular stress on the "fundamental biogenetic law" that ontogeny recapitulates phylogeny, that the organism in its development is to a great extent an epitome of the form-modi fications undergone by the successive ancestors of the species in the course of their historic evolution. Haeckel's well-known "gastraea" theory is an outcome of this generalization. He divided animal creation into the Protozoa or unicellular animals, and the Metazoa or multicellular animals. In the Metazoa the single primitive egg-cell is transformed by cleavage into a globular mass of cells (morula), which first becomes a hollow vesicle and then changes into the gastrula. The simplest multicellular animal resembles this gastrula with its two primary layers, ectoderm and endoderm, and the earliest hypothetical form of this kind, from which the higher animals are probably descended, may be called the "gastraea." Haeckel was the first to draw up a genealogical tree of the relationship between the various orders of animals. His efforts in this direction culminated in the paper he read before the fourth International Zoological Congress, held at Cambridge in 1898, when he traced the descent of the human race in 26 stages from organisms like the still-existing Monera, simple structureless masses of protoplasm, and the unicellular Protista, through the chimpanzees and the Pithecanthropus erectus, which he regarded as the link between primitive man and the anthropoid apes.
Haeckel's attempt to apply the doctrine of evolution to the problems of philosophy and religion appeared in Die Weltratsel (1899, Eng. trans. The Riddle of the Universe, 1900). Adopting an uncompromising monistic attitude, he asserted the essential unity of organic and inorganic nature. For him the chemico physical properties of carbon in its complex albuminoid com pounds are the sole and the mechanical cause of the specific phe nomena of movement which distinguish organic from inorganic substances, and the first development of living protoplasm, as seen in the Monera, arises from such nitrogenous carbon-corn pounds by spontaneous generation. Psychology he regarded as merely a branch of physiology. Every living cell has psychic properties, and the psychic life of multicellular organisms is the sum-total of the psychic functions of the cells of which they are composed. Moreover, just as the highest animals have evolved from the simplest forms of life, so the highest human faculties have evolved from the soul of animals. Consequently Haeckel denied the immortality of the soul, the freedom of the will, and the existence of a personal God.
Although Haeckel occupies no serious position in the history of philosophy, there can be no doubt that he was very widely read in his own day, and that he is very typical of the school of extreme evolutionist thought. He died at Jena on Aug. 8, 1919.
Haeckel's other works include : Die systematische Phylogenie (1894), which has been pronounced his best book; Anthropogenie (1874, 5th ed. 1903, Eng. trans. 1879), dealing with the evolution of man; Uber unsere gegenwertige Kenntnis vom Ursprung des Menschen (1898, Eng. trans. 1898) ; Der Kampf um den Ent wickelungsgedanken (19o5, Eng. trans. 1906) ; books of travel such as Indische Reisebriefe (1882, 6th ed. 1922) and Aus Insulinde Owl); Kunst f ormen der Natur (1904) and Wander bilder (19o5), reproductions of his oil paintings and water-colours.
See W. Bolsche, E. Haeckel. Ein Lebensbild (Dresden, 'goo, Eng. trans. 1906) ; Breitenbach, E. Haeckel (Odenkirchen, 1904) ; W. May, Ernst Haeckel; Versuch einer Chronik seines Lebens and Werkens (Leipzig, 1909) ; K. Hauser, E. Haeckel ... seine Bedeutung fur den Geisteskampf der Gegenwart (192o). H. Schmidt has edited the Erin nerungen and Brie f e der Liebe (1927).