Complex sentence: 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.
Split into simpler sentences: The eclipse of Darwinism was a phrase used by Julian Huxley to describe the state of affairs prior to the modern evolutionary synthesis. At that time evolution was widely accepted in scientific circles but relatively few biologists believed that natural selection was its primary mechanism.