dropping vs procreation

dropping

noun
  • The act of something that drops or falls. 

  • Something dropped; a droplet. 

  • A piece of animal excrement; dung. 

procreation

noun
  • The process by which an organism produces others of its biological kind 

  • The sexual activity of conceiving and bearing biological offspring 

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