hierarchy vs pecking order

hierarchy

noun
  • A social, religious, economic or political system or organization in which people or groups of people are ranked with some superior to others based on their status, authority or some other trait. 

  • A body of authoritative officials organized in nested ranks. 

  • Any group of objects ranked so that every one but the topmost is subordinate to a specified one above it. 

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 hierarchy and pecking order occurred in a corpus of books? (source: Google Ngram Viewer )