The eclipse of Darwinism

Julian Huxley used the phrase "the eclipse of Darwinism"[lower-alpha 1] to describe the state of affairs prior to what he called the "modern synthesis". During the "eclipse", evolution was widely accepted in scientific circles but relatively few biologists believed that natural selection was its primary mechanism.[2][3] Historians of science such as Peter J. Bowler have used the same phrase as a label for the period within the history of evolutionary thought from the 1880s to around 1920, when 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, or at least to be of relatively minor importance.[4][5]

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Four major alternatives to natural selection were in play in the 19th century:

• Theistic evolution, the belief that God directly guided evolution[lower-alpha 2]
• Neo-Lamarckism, the idea that evolution was driven by the inheritance of characteristics acquired during the life of the organism
• Orthogenesis, the belief that organisms were affected by internal forces or laws of development that drove evolution in particular directions
• Mutationism, the idea that evolution was largely the product of mutations that created new forms or species in a single step.

Theistic evolution had 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; mainstream biology largely abandoned them only when developments in genetics made them seem increasingly untenable, and when the development of population genetics and the modern synthesis demonstrated the explanatory power of natural selection. Ernst Mayr wrote that as late as 1930 most textbooks still emphasized such non-Darwinian mechanisms.[6]