The most common and most likely answer to this crossword clue is the 9 letter word DARWINISM
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More clues leading to the result DARWINISM
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The straight part
We know that "theory of evolution" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case theory of evolution = darwinism.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DARWINISM mean?
DARWINISM noun- Various concepts of development or evolution popularised by Charles Darwin's publication of On the Origin of Species in 1859.
- The principles of natural selection set out in Charles Darwin's On the Origin of Species (1859), more strictly defined by August Weismann and developed by other authors into a central part of the modern evolutionary synthesis.