Mule is an example of:
Hybrid sterility reflects key principle in quiz on speciation+pyqs, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Hybrid sterility aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Hybrid sterility fits helps integrate natural selection, environment.
Ref: Coyne & Orr, Speciation, Chapter 1: Species Concepts and Isolation.