This Day in Philosophy — 9 August: the death of Ernst Haeckel

The German zoologist and thinker Ernst Haeckel died on 9 August 1919 at Villa Medusa, his house in Jena. He had spent the last fifty-eight years of his life in that city.

Darwin in German#

After the publication of On the Origin of Species, Haeckel became the most influential advocate of the theory of evolution in Germany. But he did not confine himself to passing it on; he set the theory inside a philosophical frame of his own.

A good many of the terms we use today come from him: ecology, phylogeny and stem cell (Stammzelle) are among the words he gave to the language of science.

His best known — and most disputed — claim is the biogenetic law: ontogeny recapitulates phylogeny. That is, the embryonic development of the individual replays, in abbreviated form, the evolutionary history of the species. The formula was largely abandoned in the twentieth century, and some of Haeckel's embryo drawings were found to have been tidied up well beyond what the specimens warranted. Even so, the concept has kept its place in the history of science as one of the textbook examples of the powerful but false generalisation.

Monism: science or world-view?#

For philosophy, Haeckel's real importance lies in his turning evolution into a world-view. The Riddle of the Universe (Die Welträthsel), published in 1899, sold hundreds of thousands of copies and became one of the most widely read works of popular science of its day.

The thesis of the book is monism: mind and matter, nature and God are not two separate realities; there is a single nature, and everything is immanent in it. Haeckel also tried to organise the view into something like a scientific religion, founding the Monist League in 1906.

The question he left#

Haeckel's legacy is open today to a double reading. On the one hand he carried to a wide readership the territory where the natural sciences intersect with philosophy — the argument still pursued under the headings of the philosophy of science and naturalised metaphysics. On the other, his habit of drawing social and political conclusions directly from scientific findings took dangerous forms in later generations; his writings on race and society are handled critically for that reason.

The real question he left is still open: at what point does a scientific theory begin to turn into a world-view — and once it has turned, is it still science?