devolve vs retain

devolve

verb
  • To delegate (a responsibility, duty, etc.) on or upon someone. 

  • To be inherited by someone else; to pass down upon the next person in a succession, especially through failure or loss of an earlier holder. 

  • To degenerate; to break down. 

  • To fall as a duty or responsibility on or upon someone. 

retain

verb
  • To employ by paying a retainer. 

  • To hold back (a pupil) instead of allowing them to advance to the next class or year. 

  • To keep in one's pay or service. 

  • To keep in possession or use. 

  • To hold secure. 

How often have the words devolve and retain occurred in a corpus of books? (source: Google Ngram Viewer )