Just like their human counterparts, some dogs develop psychological abnormalities, which in their complexity, often mimic similar disturbances in humans. some breeds appear to carry a genetic predisposition for some of these behavioral traits.
Fortunately the standard and miniature schnauzers seem free of these genetically-linked disturbances, and if they are intelligently trained and cared for, they make excellent companion dogs for young and old alike.
Many animal observers note that schnauzers may, like other dog breeds, exhibit special fondness for one member of the family over the rest, but it is almost unheard of for the dog to display open aggression toward a household resident. In those very rare instances where this occurs, it can almost always be traced to mistreatment of the dog by that person.
Happily the giant, standard, and miniature schnauzer are not inherently vicious breeds whose militant protective instincts are easily released.