Historical Linguistics and Language Families 9, Exercise 3: Esperanto

Three facts (Wikipedia, Esperanto):
  - Created by L. L. Zamenhof; first grammar, Unua Libro, published 1887 under
    the pseudonym "Doktoro Esperanto".
  - Vocabulary, syntax and semantics come mainly from Indo-European
    languages; about 80% of vocabulary derives from Romance languages, the
    rest from Germanic, Greek and Slavic.
  - Classed as an international auxiliary language and an a posteriori
    language.

Why "which family?" is hard: the language was designed, not inherited by
regular change from a proto-language, and its vocabulary comes from several
branches.

Inference (mine, not the source's): that the family-tree model does not apply
to Esperanto's origin. The source does not say whether it sits outside every
family.