Scientist: rising radical gains success (6)
I believe the answer is:
darwin
'scientist' is the definition.
(Darwin is an example)
'rising radical gains success' is the wordplay.
'rising' shows that the letters should be reversed in order (going up in a down clue).
'radical' becomes 'rad'.
'gains' says to put letters next to each other.
'success' becomes 'win'.
'rad' back-to-front is 'dar'.
'dar'+'win'='DARWIN'
(Other definitions for darwin that I've seen before include "Evolution theorist" , "Naturalist, author" , "Northern Australia port" , "Man of note" , "Turn inward for the antipodean city" .)