adopt vs take on

adopt

verb
  • To take by choice into the scope of one's responsibility. 

  • To take voluntarily (a child of other parents) to be in the place of, or as, one's own child. 

  • To take or receive as one's own what is not so naturally. 

  • To obtain (a pet) from a shelter or the wild. 

  • To select and take or approve. 

  • To beat an opponent ten times in a row. 

take on

verb
  • To assume or take responsibility for. 

  • To (attempt to) dribble round (an opposition player). 

  • To catch on, do well; to become popular. 

  • To obtain the services of (a person) in exchange for remuneration; to give someone a job. 

  • To begin to have or exhibit. 

  • To attempt to fight, compete with, or engage with. 

  • To acquire, bring in, or introduce. 

  • To grieve or be concerned (about something or someone). 

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