constancy vs mutation

constancy

noun
  • The quality of being constant; steadiness or faithfulness in action, affections, purpose, etc. 

  • An unchanging quality or characteristic of a person or thing. 

mutation

noun
  • An alteration a particular sound of a word, especially the initial consonant, which is triggered by the word's morphological or syntactic context and not by its phonological context. 

  • A group of thrushes. 

  • Any alteration or change. 

  • A mutant. 

  • Any heritable change of the base-pair sequence of genetic material. 

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