caste vs pecking order

caste

noun
  • A separate and fixed order or class of persons in society who chiefly associate with each other. 

  • Hyponyms: Brahmin, Kshatriya, Shudra, Vaishya, varna 

  • Any of the hereditary social classes and subclasses of South Asian societies. 

  • A class of polymorphous eusocial insects of a particular size and function within a colony. 

pecking order

noun
  • The usually informal hierarchy of authority or command, often partial or approximate, as determined by the especially natural propensity for domination of different members of a specific group over each other, such as older brothers and sisters over their younger siblings. 

  • The natural hierarchy of social status and dominance occurring in a group of birds. 

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