Haeckel, Ernst Heinrich (ĕrnst hĪnˈrĭkh hĕˈkəl) [key], 1834–1919, German biologist and philosopher. He taught (1862–1909) at the Univ. of Jena. An early exponent of Darwinism in Germany, he evolved a mechanistic form of monism based on his interpretation of Darwin's theories and set forth in his speculative popular works on science, Generelle Morphologie (1866), The History of Creation (1868, tr. 1906), and The Evolution of Man (1874, tr. 1910). Although many of his conclusions have been proved erroneous, they attracted a large following and stimulated research. He developed a theory of recapitulation, illustrated by his gastraea theory, wherein he postulated a hypothetical ancestral form (gastraea) represented by the gastrula stage of individual development. He is known also for his study of invertebrate marine organisms, especially the Radiolaria and sponges.
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