Evolution theorist (6)
I believe the answer is:
darwin
'evolution theorist' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for darwin that I've seen before include "He propounded the Theory of Evolution" , "Naturalist with a theory on evolution" , "Evolution scientist and city" , "I'd warn this natural scientist" , "Charles ... who put forward theory of evolution" .)