Although there are no written records on their origin, Miniature Schnauzers are thought to have originated from crossing Standard Schnauzers with other smaller breeds of dog. (pethelpful.com)
Originally intended to keep rats out of barns, they were derived from a mix of Standard Schnauzers, Affenpinschers and possibly Miniature Pinschers. (dogster.com)
Heinrich Schott and Georg Riehl are thought to have miniaturized this breed by line breeding and cross breeding smaller puppies from Standard Schnauzer litters. (dogbreedanswers.com)