A crude "first cut" at this is to use the patterncount function:
Patterncount ( wsdl_load_results ; "Evolution" )
But this will also count words that contain this text such as "evolutionary"--so it may not be precise enough for your needs.
A more sophisticated approach might be something like this:
Let ( Tlist = Substitute ( wsd_load_results ; ["_" ; ¶ ] ; [" " ; ¶ ] ) ; //you may need to include more "word separators" than "_" and " "
PatternCount ( ¶ & Tlist & ¶ ; ¶ & "Evolution" & ¶ )
Whether you need such additional sophistication or not is something that is up to you to determine.
I don't know how I forgot PatternCount!!!
This works perfect, as the only word it will ever contain is Evolution, no other forms of the word.