Breeds > Mixed Breeds...

A healthy 13-year-old mixed-breed dog shows hybrid vigor.

A mixed-breed dog (also called a bastard, mutt (shortened from muttonhead), crossbreed, mongrel, tyke, cur, or random-bred dog, see Terms for mixed-breed dogs, below) is a dog that is a mixture of two or more breeds, or a descendant of feral or pariah dog populations.

Since, except for extreme variations in size, dogs interbreed freely, mixed-breed dogs vary in size, shape, and color, making them hard to classify physically. Historically, all purebred dogs have been selected from a mixed-breed population. See Golden Retriever for an example.