Gradual development (9)
I believe the answer is:
evolution
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gradual development</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for evolution that I've seen before include "Gradual change" , "Gradual development" , "Darwin's theory" , "Development - progress" , "Slow change" .)