heterogeneity vs subspecies

heterogeneity

noun
  • A composition of diverse parts. 

  • Diversity 

  • The quality of a substance which is not uniform. 

subspecies

noun
  • A subdivision of a species in other scientific disciplines. 

  • A taxon at that rank, often indicated with trinomial nomenclature (such as Felis silvestris silvestris in zoology and Pinus nigra subsp. salzmannii in botany). 

  • A rank in the classification of organisms, below species. 

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