Haeckel

Ernst Heinrich Philipp August Haeckel (1834–1919) was a German biologist, physician, and philosopher who played a pivotal role in popularizing Darwin's theory of evolution in German-speaking Europe. His work spanned zoology, embryology, and the philosophy of science, and he helped shape early ideas about ontology and ecology.

From 1866 he published Generelle Morphologie der Organismen, a major synthesis in which he argued that all organisms share a common ancestry and outlined his monistic philosophy that sought to unite science and philosophy. In this work he introduced the taxonomic concept Monera, a primitive kingdom comprising bacteria and other simple forms, and he proposed a three-kingdom scheme that classified life into Animalia, Plantae, and Protista.

Alongside taxonomy, Haeckel advanced ideas in developmental biology. He formulated the biogenic law, often summarized as ontogeny recapitulates phylogeny, which posited that an organism's development retraces its evolutionary history (a view later revised). He also produced famous embryological diagrams, collectively known as Haeckel's embryos, which later drew criticism for exaggeration.

Another lasting contribution is his coining of the term ecology (oekologie) and his advocacy of the unity of nature through monism, emphasizing natural explanations for life and society. He published The Riddle of the Universe and other works outlining a naturalistic worldview.

Controversies surround him: some of his scientific illustrations and ideas about evolution were disputed, and he endorsed or implied racial and eugenic ideas common in his era, which have been rejected by modern science. Despite this, his influence on the development of evolutionary biology, embryology, and ecological thinking remains notable.