family tree vs gens

family tree

noun
  • The totality of someone's ancestors and offspring 

  • A diagrammatic representation of a pedigree, illustrating the connections between a person's ancestors, offspring and other relatives 

gens

noun
  • A legally defined unit of Roman society, being a collection of people related through a common ancestor by birth, marriage or adoption, possibly over many generations, and sharing the same nomen gentilicium. 

  • A tribal subgroup whose members are characterized by having the same descent, usually along the male line. 

  • A host-specific lineage of a brood parasite species.^([W]) 

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