The Eclipse of Darwinism

The eclipse of Darwinism was a phrase used by Julian Huxley to describe the state of affairs prior to the modern evolutionary synthesis when evolution was widely accepted in scientific circles but relatively few biologists believed that natural selection was its primary mechanism. Historians of science such as Peter J. Bowler have used it as a label for the period within the history of evolutionary thought from the 1880s through the first couple of decades of the 20th century when a number of alternatives to natural selection were developed and explored, as many biologists considered natural selection to have been a wrong guess on Charles Darwin's part, and others felt it was of relatively minor importance.

There were four major alternatives to natural selection in the late 19th century. Theistic evolution was the belief that God directly guided evolution. (This should not be confused with the more recent use of the term theistic evolution, referring to the theological belief about the compatibility of science and religion.) The idea that evolution was driven by the inheritance of characteristics acquired during the life of the organism was called neo-Lamarckism. Orthogenesis was the belief that organisms were affected by internal forces or laws of development that drove evolution in particular directions, and saltationism was the idea that evolution was largely the product of large mutations that created new species in a single step.

Theistic evolution largely disappeared from the scientific literature by the end of the 19th century as direct appeals to supernatural causes came to be seen as unscientific. The other alternatives had significant followings well into the 20th century; it wasn't until developments in genetics made them seem increasingly untenable, and the development of population genetics and the modern evolutionary synthesis demonstrated the explanatory power of natural selection that they were largely abandoned. Ernst Mayr wrote that as late as 1930 most textbooks still emphasized such non-Darwinian mechanisms.